Interior Lighting

Interior Lightingfor DesignersFOURTH EDITION

Gary Gordon FIES, FIALD, LC

Illustrations by Gregory F. Day

John Wiley & Sons, Inc.

Interior Lightingfor Designers

About the cover photograph: The developer of this midtown-Manhattan residentialtower wanted to lure young, affluent apartment seekers to a less-than-glamorousneighborhood. He relied on architecture to do it. The lighting concept reinforces thearchitect’s asymmetrical, “anti-classical” approach: there is no traditional bottom-middle-top. The white, plaster wall is lighted with floor-mounted 100PAR/HIR lamps12” on center. A rough, industrial, Italian, factory floor lamp is paired with a soft,Japanese, paper-shade pendant to contribute to the residential scale. The buildingfully rented six months after the lobby’s completion, 18 months ahead of schedule.

Gary Gordon received the 2000 Illuminating Engineering Society Lumen Award andthe 2000 International Illuminating Design Award for this project. The New GothamLobby, Stephen Alton Architects. Photo by Eduard Hueber.

Interior Lightingfor DesignersFOURTH EDITION

Gary Gordon FIES, FIALD, LC

Illustrations by Gregory F. Day

John Wiley & Sons, Inc.

The photographs, illustrations, and other information in this book have been obtained frommany sources, including commercial soucres and private individuals. The author and pub-lisher have made every effort to obtain permission from the original copyright holders. Per-mission has been obtained except in cases where the original copyright holder could not beidentified or contacted.

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Copyright © 2003 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data

Gordon, Gary, 1957-Interior lighting for designers / Gary Gordon ; illustrations by

Gregory F. Day.— 4th ed.p. cm.

Includes bibliographical references and index.ISBN 0-471-44118-X (Cloth)

1. Electric lighting. 2. Lighting, Architectural and decorative. I. Title.TK4175 .G67 2003729’.28—dc21

2002152368

Printed in the United States of America10 9 8 7 6 5 4 3 2 1

For

my grandfather,

Louis Becker,

who first inspired me to look at buildings

Contents

Preface to the Fourth Edition xi

Acknowledgments xiii

Introduction 1

1Perception 3

Visible Light 3The Eye 4The Brain 6Brightness Perception 6Color Perception 9The Sense of Sight 10

2Psychology 11

Emotional Impact 11Degrees of Stimulation 11Degrees of Brightness Contrast 12The Three Elements of Light 14Subjective Impressions 18Variation 23

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3Brightness 25

Direction and Distribution of Light 25

Surface Finishes and Reflectances 31

Three-Dimensional Form 31

Glare and Sparkle 35

4Color 43

Color Temperature 45

Color Rendering 45

Subjective Impressions 46

Surface Finishes and Color of Light 46

5Daylight 51

Daylight Design 52

Shading Devices 56

Glazing Materials 60

Quantity 60

Energy Control 62

6Incandescent Lamps 63

Lamp Bases 64

Filaments 64

Light Output 68

Lamp Types 69

Tungsten-Halogen Lamps 73

Low-Voltage Lamps 75

Colored Light 77

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I N T E R I O R L I G H T I N G F O R D E S I G N E R S

7Discharge Lamps 81

Fluorescent Lamps 81High-Intensity Discharge (HID) Lamps 92Low-Pressure Sodium (LPS) Lamps 97

8Auxiliary Equipment 99

Transformers 99Ballasts 100

9Light Control 105

Reflection 105Transmission 109Refraction 111Glare Control 118

10Photometrics 121

Measurement of Light 121Recommended Illuminance Values 124Illuminance Calculations 126Surface Reflectance 133

11Electricity 135

Principles of Electricity 135Switch Control 139Dimming Control 141Central Lighting Control Systems 146

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C O N T E N T S

12Luminaires 149

Housings 149Light and Glare Control 154

13Design 209

Visual Clarity 209Architectural Surfaces 213Task Lighting 218Ambient Lighting 220Lighting Art 224Balance of Brightness 229Energy-Effective Design 237Integrating Light and Architecture 239

Appendix 243

References 271

Credits 273

Glossary 277

Index 285

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Preface to theFourth Edition

This Fourth Edition expands upon the foun-dation established in the previous edition,with the added benefit of greater claritythroughout. While it retains the mark of thethorough copy and technical edit providedfor the Third Edition by the late luminaire-design genius Edison Price, chapters 9, 10,and 11 have been reorganized to correspondmore closely with professional practice. Newto this edition is material on the latestadvances in lighting technology and prac-tice; state-of-the-art light sources, equip-ment, and systems; and a comprehensiveglossary. For the first time, an Instructor’sManual is available on-line from the pub-lisher to accompany the text.

As with the Third Edition, this book isintended to serve as both a textbook forarchitecture and interior design studentsand a manual for practicing professionals. Itprovides a simple framework for understand-ing the lighting design process. More than250 line drawings, photographs, and colorplates, many of them new to this edition,illustrate the text. The design of light for inte-

riors is emphasized; tools and techniquesare presented as a means by which toachieve the design. This is an architecturalapproach to lighting design, based on myapprenticeship with the talented architectand lighting designer Carroll Cline, as well astwenty years of professional practice.

The lighting design process outlined inthis book parallels the methodology used bylighting professionals to provide solutions forarchitectural interiors around the world. Ideveloped this system for describing thelighting design process while teaching grad-uate and undergraduate students at the Par-sons School of Design Lighting Institute inNew York City. The success of this method isdemonstrated by the great number of myformer students who professionally practicelighting design today.

ACKNOWLEDGMENTSThis work owes an enormous debt to CarylGordon and Mary Hebert for their help withcopy-editing and proofreading; to Dr. KevinHouser for his exceptionally thorough techni-

xi

cal edit; and to David Marini for his assis-tance with the layout and design.

Valuable research assistance was pro-vided by the able crew of the Gary GordonLLC office in New York: Kevin Frary, JustinHorvath, Michael Haslam, Christine Kong,Ryan Stromquist, Rob Thomas, and RyanWither. Rob Thomas skillfully coordinated allof the drawings, color plates, and photo-graphs.

I am also grateful for the support ofAneeahseah Lefler and Jennifer Downey. AtJohn Wiley & Sons, Amanda Miller providededitorial guidance, and Jennifer Ackermanmade working on this book a joy.

Gary Gordon FIES, FIALD, LCNew York, New YorkSeptember 2002

xii

Introduction

Lighting design is a process. It is the processof integrating light into the fabric of architec-ture. Regardless of the space to be lighted—a bank, a church, an office, a gallery, a res-taurant, a store, a classroom—and regard-less of the light sources available for use, theprocess is always the same.

Because lighting design is a process, itcan be learned. This book traces the steps inthe lighting design process much as a pro-fessional performs them in practice. Design,of course, is not always a linear process. Attimes some of these steps are used simulta-neously. But, on the whole, the order of thematerial corresponds to professional prac-tice.

This book does not describe the lightingdesign process; it describes a lighting designprocess. It is one that has been usedsuccessfully by Gary Gordon LLC to providesolutions for more than one thousand archi-tectural projects around the world. It is a pro-cess built on the conviction that the lightingcondition of a space has enormous emo-tional impact on people.

A common mistake when providing lightfor buildings is to select the lighting equip-ment first. Selecting luminaires is the laststep in the process. What is important is not

what makes the light, but which objects andsurfaces receive it. The key to successfullighting design is to decide what you want tolight first, and then work backward to deter-mine the solution.

In chapter 1, we learn by understandingthe human visual system that perception ofthe world around us is based not on thequantity of light entering the eye but on thequantity of contrast. In chapter 2, we learnfrom psychology that because the sense ofsight is contrast-sensitive, the brightnesscontrast of a space determines its emotionalimpact. In chapter 3, we learn how the direc-tion and distribution of light determine thebrightness contrasts that yield the desiredemotional setting.

Once the emotional setting and bright-ness contrast have been established, webegin our selection of light sources by deter-mining the color of light in chapter 4. The nextthree chapters provide a thorough knowledgeof light sources, from daylight (chapter 5)through incandescent and tungsten-halogen(chapter 6) to discharge sources: fluorescent,mercury, metal halide, and high-pressuresodium (chapter 7). Chapter 8 describes theauxiliary equipment required to operate dis-charge and low-voltage incandescent lamps.

1

Chapter 9 explains the external devicesemployed to modify light sources so thatthey provide the desired direction and distri-bution of light and control glare. With thelight source modified, Chapter 10 illustrateshow we use photometry to predict the quan-tity of light in completed space. Chapter 11provides an understanding of the electricalrequirements of light sources and methodsof lighting system control.

Once the source, with its externaldevices, methods of modifying distributionand controlling glare, and electrical require-ments, is established, we are at last ready toselect the luminaire in chapter 12. It is onlyat this point in the lighting design processthat a suitable luminaire can be chosen:after the designer has identified the activityin a space and degree of contrast required,and has determined the color of light, light

sources, modifications to control source dis-tribution and glare, and locations of lightsources.

Our final chapter looks at the elementsthat produce visual clarity; design tech-niques for lighting architectural surfaces,tasks, and art; the balance of brightness;energy-effective design; and integrating lightand architecture.

The architectural lighting design processdescribed in this book produces a spacewhere the casual observer is unaware of themechanics of light production; he perceivesonly a comfortable environment that sup-ports his activities and enhances his well-being. With practice, the designer learns toapply this process in ways that go even fur-ther, producing environments that stimulatethe mind and inspire the spirit.

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PerceptionPerception of the world around us is based not on the quantity of light entering

the eye, but on the quantity of contrast.

VISIBLE LIGHTWhat we perceive as light is a narrow bandof electromagnetic energy, ranging fromapproximately 380 nanometers (nm) to 760nm. Only wavelengths in this range stimulatereceptors in the eye that permit vision (figure1.1 and color plate 1). These wavelengthsare called visible energy even though wecannot directly see them.

In a perfect vacuum, light travels atapproximately 186,000 miles per second.When light travels through glass or water oranother transparent substance, it is sloweddown to a velocity that depends on the den-sity of the medium through which it is trans-mitted (figure 1.2). This slowing down of lightis what causes prisms to bend light andlenses to form images.

When light is bent by a prism, eachwavelength is refracted at a different angleso the emergent beam emanates from the

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1

Figure 1.1 Visible light is a narrow region of the totalelectromagnetic spectrum, which includes radio waves,infrared, ultraviolet, and x-rays. The physical differenceis purely the wavelength of the radiation, but the effectsare very different. Within the narrow band to which theeye is sensitive, different wavelengths give differentcolors. See also color plate 1.

prism as a fan of light, yielding all of thespectral colors (see color plate 2).

All electromagnetic radiation is similar.The physical difference between radio waves,infrared, visible light, ultraviolet, and x-rays istheir wavelength. A spectral color is light of aspecific wavelength; it exhibits deep chro-matic saturation. Hue is the attribute of colorperception denoted by what we call red,orange, yellow, green, blue, and violet.

THE EYEA parallel is often drawn between the humaneye and a camera. Yet visual perception

involves much more than an optical imageprojected on the retina of the eye and inter-preted “photographically” by the brain.

The human eye is primarily a device thatgathers information about the outside world.Its focusing lens throws a minute invertedimage onto a dense mosaic of light-sensitivereceptors, which convert the patterns of lightenergy into chains of electrical impulses thatthe brain will interpret (figure 1.3).

The simplest way to form an image is notwith a lens, however, but with a pinhole. Infigure 1.4, a ray from each point of theobject reaches only a single point on the

4


Figure 1.2 The law of refraction (Snell’s law) states that when light passes from medium A into medium B the sine of theangle of incidence (i) bears a constant ratio to the sine of the angle of refraction (r).

Figure 1.3 Cross section of the human eye.

screen, the two parts being connected by astraight line passing through the pinhole.Each part of the object illuminates a corre-sponding part of the screen, so an upside-down image of the object is formed. The pin-hole image is dim, however, because thehole must be small (allowing little light topass through) if the image is to be sharp.

A lens is able to form a much brighterimage. It collects a bundle of light rays fromeach point of the object and directs them tocorresponding points on the screen, thusgiving a bright image (figure 1.5).

The lens of the human eye is built upfrom its center, with cells being added allthrough life, although growth gradually slowsdown. The center is thus the oldest part, andas the cells age they become more compactand harden. As a result, the lens stiffens andis less able to change its shape to accom-modate varying distances (presbyopia)(figure 1.6).

Lenses work well only when they fit prop-erly and are adjusted correctly. Sometimesthe lens is not suited to the eye in which itfinds itself: (1) the lens focuses the image in

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P E R C E P T I O N

Figure 1.4 Forming an image with a pinhole.

Figure 1.5 Forming an image with a lens. The lens shown is a pair of prisms; image-forming lenses have curved surfaces.

front of or behind the retina instead of on it,giving “short” sight (nearsighted or myopic)or “long” sight (farsighted or hyperopic); (2)the lens is not truly spherical, giving distor-tion and, in some directions, blurring of theimage (astigmatic); or (3) the cornea is irreg-ular or pitted.

Fortunately, almost all optical defectscan be corrected by adding artificial lenses,which we call eyeglasses. Eyeglasses correctfor errors of focus (called accommodation)by changing the power of the lens of the eye;they correct for distortion (called astigma-tism) by adding a nonspherical component.Ordinary glasses do not correct damage tothe surface of the cornea, but corneallenses, fitted to the eye itself, serve to give afresh surface to the cornea.

The iris is the pigmented part of the eye.It is found in a wide range of colors, but thecolor has no impact on vision as long as it isopaque. The iris is a muscle that forms thepupil. Light passes through the pupil to thelens which lies immediately behind it. This

muscle contracts to reduce the aperture ofthe lens in bright light and also when theeyes converge to view near objects.

The retina is a thin sheet of intercon-nected nerve cells, which include the light-sensitive cells that convert light into electri-cal impulses. The two kinds of light-receptorcells—rods and cones—are named aftertheir appearance as viewed under a micro-scope (figure 1.7).

Until recently, it was assumed that thecones function in high illuminance, providingcolor vision, and the rods function under lowilluminance, yielding only shades of gray.Color vision, using the cones of the retina, iscalled photopic; the gray world given by therods in dim light is called scotopic.

Recent research, however, suggeststhat both rods and cones are active at highilluminance, with each contributing to differ-ent aspects of vision. When both rods andcones are active, vision is called mesopic.

THE BRAINThe eyes supply the brain with informationcoded into chains of electrical impulses. Butthe “seeing” of objects is determined onlypartially by these neural signals. The brainsearches for the best interpretation of avail-able data. The perception of an object is ahypothesis, suggested and tested by sensorysignals and knowledge derived from previousexperience.

Usually the hypothesis is correct, andwe perceive a world of separate solid objectsin a surrounding space. Sometimes the eval-uation is incorrect; we call this an illusion.The ambiguous shapes seen in figures 1.8and 1.9 illustrate how the same pattern ofstimulation at the eye gives rise to differentperceptions.

BRIGHTNESS PERCEPTIONWe speak of light entering the eye, calledluminance, which gives rise to the sensation

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Figure 1.6 Loss of accommodation of the lens of theeye with aging.

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P E R C E P T I O N

Figure 1.8 Necker cube. When you stare at the dot,the cube flips as the brain entertains two different depthhypotheses.

Figure 1.9 Ambiguous shapes. Is it a vase or two facesin profile?

Figure 1.7 The retina.

of brightness. Illuminance, which is the den-sity of light received on a surface, is mea-sured by various kinds of photometers,including the familiar photographer’s expo-sure meter.

Brightness is a subjective experience.We hear someone say, “What a bright day!”and we know what is meant by that. But thissensation of brightness can be only partlyattributed to the intensity of light enteringthe eyes.

Brightness is a result of: (1) the intensityof light falling on a given region of the retinaat a certain time, (2) the intensity of lightthat the retina has been subject to in therecent past (called adaptation), and (3) theintensities of light falling on other regions ofthe retina (called contrast).

Figure 1.10 demonstrates how theintensity of surrounding areas affects theperception of brightness. A given regionlooks brighter if its surroundings are dark,

and a given color looks more intense if it issurrounded by its complementary color.

If the eyes are kept in low light for sometime they grow more sensitive, and a givenquantity of light will seem brighter. This “darkadaptation” is rapid for the first few seconds,then slows down. As the eye becomes darkadapted, it loses acuity while it gains sensi-tivity. With a decrease of intensity and thecompensating dark adaptation, the ability tomake out fine detail is lost.

The cone and rod receptor cells adapt atdifferent rates: cone adaptation is com-pleted in about seven minutes; rod adapta-tion continues for an hour or more. This isdemonstrated by the difference betweenleaving a dark movie theatre and emerginginto bright daylight (cone or light adapta-tion), and its reverse: entering a dark theatrefrom a bright, sunny day (rod or dark adapta-tion).

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Figure 1.10 Simultaneous contrast.

COLOR PERCEPTIONBrightness is also a function of color. For agiven intensity, the colors at the middle ofthe spectrum look brighter than those at theends. The sensitivity curves for rods andcones are different. Their shape is similar,but the cones are most sensitive to yellow,and the rods are most sensitive to green.This change with increasing intensity isknown as the Purkinje Shift (figure 1.11).

The visible spectrum is comprised of fivecolors of light (see color plate 3) (not of pig-ment [see color plate 4]): violet, blue, green,yellow, and red. These colors can be mixed:for example, yellow is obtained by combiningred with green light.

Mixing colors of light is achieved byusing filters, prisms, or diffraction gratings.By mixing two colors of light, a third color isformed in which the two mixed colors cannotbe identified.

By mixing three colors of light andadjusting their intensities, any spectral huecan be produced. White can be made, butnot black or nonspectral colors such asbrown (see color plate 3).

When speaking technically about colorvision, we do not refer to “colors” but ratherto “hues.” This is to avoid difficulty with theterm colors, which is descriptive of the physi-ological sensations to which we give specificnames, such as “red” or “blue.” We there-fore speak technically of spectral hues ratherthan spectral colors.

Another important distinction is to befound between color as a sensation and coloras a wavelength (or a set of wavelengths) oflight entering the eye. Technically, light itselfis not colored: it gives rise to sensations ofbrightness and color, but only in conjunctionwith a suitable eye and nervous system.When we speak of “yellow light,” it meanslight that gives rise to a sensation describedby the majority of people as “yellow.”

All the colors of the spectrum are inter-preted by the brain from only three kinds ofreceptors in the eyes: violet, green, and red.These three kinds of color-sensitive recep-tors (cones) respond to blue-violet, puregreen, and orange-red; all colors are “seen”by a mixture of signals from the three sys-tems.

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P E R C E P T I O N

Figure 1.11 The Purkinje Shift.

What we perceive as white is not a par-ticular mixture of colors, but rather the gen-eral illumination, whatever this is. A candleor lamplight that looks white by itselfappears yellow when “white” electric light ordaylight is present for comparison.

The reference for what is taken as whiteshifts. Knowledge of the normal color ofobjects is called color constancy; it leads usto expect that a tomato will be red. Thebrain’s stored knowledge and expectationsexert a strong influence on color perception:objects such as oranges and lemons, forexample, take on a richer color because theyare recognized as orange and yellow.

Grass is a plant found on lawns and wecall the sensation of color it gives “green,”but we identify grass by characteristics otherthan its color: its presence as a lawn, theform and density of the blades, and so forth.If we do confuse the color, sufficient addi-tional evidence is available to identify it asgrass. We know it is supposed to be greenand we call it green, even when this is doubt-ful as in the dim light of dusk.

In 1992, neurophysiologists discoveredthat an alignment of brain cells forms thebasis of visual memory. The cells are stacked

in columns; depending on which columns areexcited by an object, the brain is able toinstantly recognize complex images such asfaces, even when presented at odd angles orwhen only part of the face is visible.

Yet it remains a mystery how the contri-butions from separate channels for bright-ness, color, shape, and movement—withtheir own locations in different regions of thebrain—come together to form consistentperceptions.

THE SENSE OF SIGHTWe do know that perception is independentof the quantity of light entering the eye; it isbased on the quantity of contrast: the differ-ences between light and dark. A certainquantity of light is necessary for a person tosee, yet the eye responds not to the totalintensity, but to the average intensity in thefield of view.

The sense of sight, therefore, is contrastsensitive. It is a mechanism for the detectionof differences: of figures on a ground, ofobjects in a surround. Subjective impres-sions of space are a function of the degree ofcontrast present in the environment.

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PsychologyBecause the sense of sight is contrast sensitive, the brightness contrast of a

space determines its emotional impact.

EMOTIONAL IMPACTSubjective impressions of space are a func-tion of brightness contrast: the relationshipof surfaces that are lighted (the focus orforeground) to those that are left in compar-ative darkness (the surround or background).It is possible, of course, to simply introducegeneral illumination into a room to permitvision. But establishing the emotionalimpact of an interior through the manipula-tion of brightness contrast is the real chal-lenge for the creative designer.

Reliance on published standards forilluminance on the workplane leads uninten-tionally to environments that are sterile andunstimulating. Proper attention to the manip-ulation of brightness contrast as a principaltechnique for the design of lighting systemsresults in environments that are inviting,inspiring, and supportive of the tasks to beperformed.

If all objects and surfaces in a roomreceive equal emphasis from light, contrastis lost. Over time, the lack of contrast causes

people to feel listless and depressed. With-out contrast, the environment produced hasthe quality of a cloudy, overcast day.

People feel more alert, energetic, andpositive on a sunny day, which is marked bybright highlights and crisp shadows. By pro-viding brightness contrast, an environmentmay be created that has the attributes of asunny day. In truth, the significant differencebetween a “dull, dreary day” and a “bright,cheerful” one is the quality of light.

DEGREES OF STIMULATIONSome activities and tasks benefit from a highdegree of stimulation to encourage partici-pation and increase enjoyment. Other activi-ties and tasks benefit from a minimum ofcontrast to help a person feel contented,comfortable, focused, and relaxed. Althoughindividuals react differently to the same envi-ronment, there is a high degree of similarityin people’s reactions to light.

Environmental psychologists use theterms high-load and low-load to describe

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2

degrees of stimulation or arousal. The morestimuli that must be processed by a person,the higher the load. Environments that arecomplex, crowded, asymmetrical, novel, unfa-miliar, surprising, or random are high load.Environments that are simple, uncrowded,symmetrical, conventional, familiar, unsur-prising, or organized are low-load.

If the task to be performed is complex orunusual—studying technical material, pre-paring for an exam, or writing an essay—theload is great enough that our degree ofarousal is fairly high; additional load from theenvironment will increase stimulation tosuch a point that the task is avoided. Webecome distracted, annoyed, or frustrated,and performance falls off sharply.

Tasks that are simple or routine—writingchecks, making a shopping list, or otherfamiliar chores—benefit from a mildly stimu-lating environment. Daydreaming or dozingmay result without increased stimulation.This is why such work often fails to be per-formed in home offices or studies designedfor paperwork; instead it is done in kitchens,dining rooms, or living rooms, which have ahigher degree of stimulation.

The lower the load of the task, the moreit requires a high-load setting for optimum per-formance. Boring tasks are boring becausethey are unstimulating (simple or overly famil-iar) and often unpleasant. Within reason, themore stimulation provided, the more pleasantthe task becomes. For many, basic houseworkis monotonous; playing background musicincreases stimulation, enabling us to complete“boring” domestic chores.

DEGREES OF BRIGHTNESS CONTRASTThe degree of brightness contrast evokesemotions in the same way as backgroundmusic. It affects the performance of tasks,influences the behavior of people at workand at play, and impacts the amount of con-

tentment and pleasure we experience. Thedegree of brightness contrast establishesthe emotional setting, which either rein-forces or undermines the intended activity.

The first step in the lighting design pro-cess is to identify the activity that will occurin a space. The second step is to determinea degree of stimulation that will reinforcethat activity. The third step is to establish thedegree of brightness contrast that will yieldthe necessary level of stimulation.

Brightness contrast is established bydeveloping patterns of light and shade—byselecting specific surfaces and objects toreceive lighting emphasis while leaving othersin comparative darkness. This emphasis cre-ates the relationship between foregroundand background (figure 2.1).

Low-Contrast EnvironmentIf everything is to receive equal emphasis, nohierarchy is established between foregroundand background. The result is a low-contrastenvironment. Low-contrast spaces are low instimulation: few stimuli exist to respond to.These spaces are behaviorally neutral (figure2.2).

A large proportion of diffuse light and asmall amount of focused light produce thislow-contrast environment. Low-contrast light-ing systems are intended to provide easyseeing for visual tasks, to allow random circu-lation, or to permit flexible relocation of worksurfaces. The diffuse lighting technique pro-vides a uniformly illuminated working environ-ment, an area suitable for difficult andsustained visual tasks (figure 2.3).

Lighting systems that flood a space withdiffuse light from overhead reduce contrast.Highly diffuse light produces a shadowlessenvironment; forms are ill-defined and tex-tural perception is poor. Although this is ade-quate for task vision, it ignores the problemcreated by the bland psychological reactionto a cloudy day.

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P S Y C H O L O G Y

Figure 2.2 Low-contrast lighting.

Figure 2.1 Patterns of light and shade establish brightness contrast.

High-Contrast EnvironmentA small proportion of diffuse light and a largeamount of focused light produce a high-con-trast environment. High-contrast lighting sys-tems render patterns of light and shade; theyintentionally establish a hierarchy betweenforeground and background. High-contrastspaces increase stimulation; they areintended to evoke specific moods or emo-tions (figure 2.4).

A single spotlight on a stage is anextreme example of the influence of bright-ness contrast in creating focal points. A roomlighted in this way dominates the people in it;the brightness contrast directs their attentionand holds their interest, producing visualdirection and focus (figure 2.5).

Attention is involuntarily drawn towardareas of brightness that contrast withthe visual background. When a personapproaches an unfamiliar space or activity,brightness contrast and color contrast help to

establish an initial response. High-contrastenvironments are useful for guiding the circu-lation of people entering an unfamiliar room.

THE THREE ELEMENTS OF LIGHTThe three fundamental elements of light are:ambient light, focal glow, and sparkle. Theratio of ambient light to focal glow estab-lishes the degree of brightness contrast in aspace; sparkle adds the highlights that con-tribute to feelings of well-being. The propor-tions of these three elements yield thedesired emotional setting.

The late lighting designer Richard Kellypoetically defines the three elements oflight. To Kelly, ambient or general light is

a snowy morning in open country . . .twilight haze on a mountain top or acloudy day on the ocean . . . the lightin a white tent at noon . . . moonlightcoming through the fog.

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Figure 2.3 Low-contrast lighting.

Figure 2.4 High-contrast lighting.

Figure 2.5 High-contrast lighting.

Ambient luminescence is shadowlessillumination. It minimizes form andbulk. It dematerializes. It reduces theimportance of things and people. Itfills people with a sense of freedom ofspace and suggests infinity. It is usu-ally reassuring and restful.

The best example is a foggy day on amountain top. There is an even glowwithout incidence all around; thereare no shadows, nothing to tell youwhat to look at. In that sense it’s con-fusing, but it is also relaxing and rest-ful, as there is no excitement, nointerest. It minimizes man—thinkabout a figure moving through thatfog—and destroys form [figure 2.6].

Focal glow or task light, for Kelly, is

the campfire of all time, the glowingembers around which stories aretold, or the football rally bonfire.Focal glow is the limelight, the followspot on the stage, and an aircraftbeacon. . . . It is the light burning atthe window or the welcoming gleamof the open door.

Focal glow is the sunburst throughthe clouds and the shaft of sunshinethat warms the far end of the valley. Itis the pool of light at your favorite read-ing chair, your airplane-seat light, ormatch-light on a face. Focal glow isthe end of the rainbow; it commandsattention, creates interest, fixes thegaze, and tells people what to look at.Focal glow is the focus. It separatesthe important from the unimportant,establishes precedence, can inducemovement, and can control traffic.

Focal light is directive, creates abright center; it tells us what to look

at, organizes, marks the most impor-tant element. It creates a sense ofspace; you can organize depththrough a sequence of focal centers[figure 2.7].

To Kelly, sparkle or glitter is:

a play of brilliants . . . the sensationof a cache of diamonds in an openedcave or the Versailles Hall of Mirrorswith its thousands of candle flames. . . a ballroom of crystal chandeliers.Play of brilliants is Times Square at

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Figure 2.6 Ambient luminescence.

night . . . sunlight on a tumblingbrook . . . the heaven full of stars. . . birch trees interlaced by a motorcar’s headlights.

Play of brilliants excites the opticnerves . . . stimulates the body andspirit and charms the senses. It cre-ates a feeling of aliveness, alerts themind, awakens curiosity, and sharp-ens the wits. It quickens the appetiteand heightens all sensations. It canbe distracting or it can be entertain-ing.

Sparkle is scintillation. It is a tinymicroscopic bombardment of points oflight—the most exciting kind of lightthere is. It stimulates and arousesappetites of all kinds; chandeliers in

dining rooms, sequins on dresses, andlights on theatre marquees all takeadvantage of the fact1 [figure 2.8].

Outdoors, during daytime, the sky pro-vides the ambient light. Objects and sur-faces that are illuminated by the sun, suchas a meadow, trees, or the side of a building,are the focal glow. The reflection of the sunfrom specular surfaces, such as movingwater, dew on leaves, or polished metal on abuilding, supplies the sparkle.

At the beach, the ambient light providedby the sky is balanced by the diffuse,

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P S Y C H O L O G Y

Figure 2.7 Focal glow.

1John Marsteller, “A Philosophy of Light: Recalling Rich-ard Kelly’s Three Functional Elements,” Interior DesignFebruary 1987: 78–80.

reflected light from the sand. Objects thatare lighted by the sun, such as sandcastles,people, bright beach blankets, and bathingsuits, become the focus. The glistening ofthe sun on the agitated water or on wetstones at the water’s edge is the sparkle.

Indoors, the proportions of these sameelements—ambient light, focal glow, andsparkle—always and everywhere determinethe emotional setting.

SUBJECTIVE IMPRESSIONSThe late professor John Flynn documentsthat as patterns of brightness contrast

change, the strength of visual stimuli alsochanges, altering our impressions of space.

While looking for evidence that lightingchanges alone elicit significantly differentreactions, Flynn tested six lighting schemeswithout making other changes in the room(figures 2.9 to 2.14). These changes in light-ing condition evoke consistent responses inthree areas of impression: spaciousness,perceptual clarity, and pleasantness.

Impressions of spaciousnessThe impression of a room’s largeness orsmallness is affected by the intensity anduniformity of the lighting at the room perime-

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Figure 2.8 Sparkle.

ter. Flynn found that differences in quantity

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P S Y C H O L O G Y

Figure 2.10 Peripheral wall lighting, all walls.

Figure 2.11 Overhead diffuse lighting, low setting. Figure 2.12 Combination: overhead downlighting +end walls.

Figure 2.13 Overhead diffuse lighting, high intensity. Figure 2.14 Combination: overhead downlighting,overhead diffuse lighting, + end walls.

Figure 2.9 Overhead downlighting, low intensity.

ter. Flynn found that differences in quantityof horizontal illuminance significantly alterimpressions of spaciousness and perceptualclarity. Higher illuminance values aredescribed as “clear,” “bright,” “distinct,”“large,” and “more spacious”2 (figure 2.15).

Impressions of perceptual clarityNothing is more important than how peo-ple’s faces appear. Flynn demonstrated thatlighting schemes rated high in facial clarityare considered more public; schemes thatare rated low in facial clarity are consideredmore private.

Public space implies intermingling andbringing people together. The potential forvisual contact improves as the intensity of

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Figure 2.15 Impressions of spaciousness (large-small).

2Improvement in visual contact continues to approxi-mately 25 footcandles (fc) of ambient horizontalilluminance, beyond which it stabilizes.

Figure 2.17 Impressions of perceptual clarity—private space.

Figure 2.16 Impressions of perceptual clarity—public space.

general illuminance is increased. Increasingintensities reduce anonymity and bringpeople together because facial expressionsand gestures are more clearly perceptible(figure 2.16).

Private space suggests separatingpeople and keeping them apart. Shadowand silhouette reinforce feelings of detach-ment and privacy because these lightingtechniques inhibit the ability to perceive pre-cise facial detail; even nearby individualsbecome more anonymous (figure 2.17).

In a crowded space, when it is impossi-ble to separate people physically by dis-tance, it is possible to separate them visually

by lighting. This technique is often used incocktail lounges, fine restaurants, andreception rooms.

Impressions of pleasantnessFlynn also found that the nonuniform bright-ness produced by a downward concentratinglighting system rates more favorably than theuniform brightness produced by a diffusesystem. The nonuniform brightness is ratedas more “friendly,” “pleasant,” “sociable,”and “interesting” (figure 2.18). Differencesin the quantity of horizontal illuminance fromoverhead systems exert negligible influenceon impressions of pleasantness.

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Figure 2.18 Impressions of pleasantness.

Vertical Surface IlluminationWhen wall lighting is added, Flynn discov-ered that ratings shift to the positive for allthree categories of impression. Lighted verti-cal surfaces reinforce feelings of spacious-ness, clarity, and pleasantness.

VARIATIONLack of variation in the built environment isan obstacle that lighting helps to overcome.Monotony results in boredom and depres-sion: even a string of bright, sunny days willbecome boring through overfamiliarity. Vari-ation increases stimulation and impressionsof pleasantness.

One way to increase the load of office orfactory environments is to introduce stimulithat vary over time; otherwise, workersquickly become accustomed to the setting.For example, areas for coffee and lunchbreaks that have greater contrast and sparklethan the workplace introduce variety througha change of the lighting condition, while alsoencouraging sociability and conversation.

People using a library, as those in theoffice and factory, benefit from more stimu-lating lighting systems in areas used fortaking breaks, socializing, or simply day-dreaming, for relief from the fatigue causedby concentrated work. The typical library hasquiet stacks and cubicles conducive to

study, and other areas for relaxed readingand scanning periodicals. People prefer lessloaded settings for difficult, complex materi-als, and more loaded spaces for casual,pleasant reading.

If workers are performing complex anddangerous tasks, however, a pleasant low-load lounge lowers their degree of stimula-tion. Conversely, performance of low-loadtasks in dull settings benefits enormouslyfrom pleasant and mildly stimulating diver-sions. If you must wade through low-loadpaperwork, such as reading reports, review-ing dull proposals, or composing routine cor-respondence, productivity is increased whenoffices are provided with a means of alteringthe lighting condition.

A fixed, ideal lighting solution that willincrease performance while a person isdoing a monotonous task is unattainable.Changing all the lamps in a factory to animproved-color light source is insufficient,for example; in time, such a static modifica-tion loses much of its stimulating value. Acontrollable variability of the lighting environ-ment is necessary and beneficial.

In addition to the lighting system, sur-face finishes, textures, and colors also con-tribute to the environmental load. In prac-tice, they all must be considered at the sametime.

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P S Y C H O L O G Y

BrightnessSpecifying the direction and distribution of light in a space yields the desired

brightness contrast.

Brightness versus luminanceBrightness is the subjective sensation thatoccurs in the consciousness of a humanobserver. Luminance is the objective mea-surement of intensity per unit of projectedarea.

DIRECTION AND DISTRIBUTIONOF LIGHTA luminaire (lighting fixture) emits light in oneof three directions—downward, upward, ormultidirectional—and in one of two distribu-tions—concentrated or diffuse (figure 3.1).

Downward light from a properly designedluminaire has a restricted angular spread;direct glare is prevented by both thisrestricted spread and the shape of the humaneyebrow. Upward light usually covers a largearea of the ceiling; the light reflected from theceiling is of low luminance and is unlikely tocause distracting glare. Multidirectional lightis emitted in all directions, but it cannot emitmuch of its output sideways without causingobjectionable glare.

Upward and downward light is emitted inpatterns that vary from narrow to wide. Con-

centrated distribution focuses light in anarrow pattern; diffuse distribution disperseslight in a wide pattern.

Luminaires with narrow beam-spreadsthat lack an upward component of light pro-duce a concentrated downward (also calleddirect) distribution (figure 3.2). Whenlocated in low ceilings, concentrated down-ward beams—with spreads of 30° or less—create areas of high luminance on the floorwith dark areas in between. To avoid thisunevenness, luminaires would need to beplaced inordinately close to each other. Lowceilings require the use of diffuse downwardluminaires.

When located in high ceilings, concen-trated downward beams overlap and avoidsuch light and dark areas, yet only horizontalsurfaces and the tops of objects are lighted;faces and walls receive little light and appearin shadow. This yields a high-contrast space,one of low ambient brightness with highbrightness accents (figure 3.3).

Luminaires with diffuse beam-spreadsand a downward distribution produce diffusedownward (direct) light (figure 3.4). Diffusedownward beams—with spreads from 80° to

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3

120°—offer a more practical light distribu-tion for many purposes. A luminaire with a100° beam-spread, emitting most of its lightbelow a cutoff angle of 40° from horizontal,is offered by most well-designed downlights.This greater percentage of light at higherangles increases incident light on verticalsurfaces, models faces, and reduces theconcentration of brightness within the

space. Diffuse downward luminaires yield alow-contrast setting (figure 3.5).

A concentrated upward (indirect) distri-bution directs light toward the ceiling (figure3.6). With light directed upward and thedownward component removed, the ceilingbecomes visually prominent. It also becomesa secondary light source because of its reflec-tive properties.

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Figure 3.1 The seven directions and distributions of light.

Figure 3.2 Concentrated downward (direct) distribu-tion.

Figure 3.3 An example of concentrated downward distribution.

When mounted in close proximity to thesurface being lighted, concentrated upwardbeams create isolated areas of high lumi-nance. The nonuniformity of concentratedupward distribution reduces the strong con-trast that results from a concentrated down-ward system by adding visual interestthrough brightness variation (figure 3.7).

If this is the main source of room illumi-nation in areas with low ceiling heights, the“spots” of high brightness on the ceilingbecome uncomfortable and cause glare.When placed farther from the surface to belighted, however, concentrated upwardbeams produce uniform brightness: eachbeam covers a wider area and multiple beampatterns overlap. In areas with higher ceilingheights, the concentrated beam has suffi-cient distance to spread; thus the ceiling islighted uniformly, reducing brightness andglare (figure 3.8).

A diffuse upward (indirect) distributiondirects light toward the ceiling and the upperside walls (figure 3.9). This technique isused to create uniform ceiling luminance for

the prevention of glare in areas with videodisplay terminals (VDTs) and to emphasizestructural form or decorative detail on ornear the ceiling plane (figure 3.10).

Because each point on the ceilingreflects light in every direction, diffuse upwarddistribution produces a flat, low-contrastenvironment: the reflected light reduces con-trast and shadow; objects and faces have thewashed-out appearance similar to thatcaused by an overcast day.

Multidirectional diffuse (general diffuse)distribution is produced by luminaires thatdeliver both upward and downward compo-nents of light (figure 3.11). These luminairesemit light in several directions at the sametime—toward the ceiling and walls as well astoward the floor. The reflected light from theceiling and the interreflection of light in thespace diffuse the downward distribution,reducing shadow and contrast and creating auniform, high-brightness interior (figure 3.12).

Luminaires that deliver both direct andindirect components of diffuse light, but no sidelighting, are called direct/indirect (figure 3.13).

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Figure 3.4 Diffuse downward (direct) distribution. Figure 3.5 An example of diffuse downward distribution.

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Figure 3.7 An example of concentrated upward distribution.

Figure 3.8 An example of concentrated upward distribution with thelight source placed farther from the illuminated surface.

Figure 3.6 Concentrated upward(indirect) distribution.

B R I G H T N E S S

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Figure 3.9 Diffuse upward (indirect) distribution. Figure 3.10 An example of diffuse upward distribution.

Figure 3.11 Multidirectional diffuse (general diffuse)distribution.

Figure 3.12 An example of multidirectional diffuse distribution.

They provide efficient use of light on worksurfaces while relieving contrast by reflectinglight from the ceiling plane (figure 3.14).

Multidirectional distribution created withconcentrated beam-spreads is called multidi-rectional concentrated (figure 3.15). It is alsocalled semidirect if 60% to 90% of the lumens(light emanating from the luminaire) aredirected downward, and semi-indirect if 60%to 90% of the lumens are directed upward.

A higher contrast, nonuniform bright-ness condition is produced with concen-trated distributions present in both theupward and downward components. Theupward component reduces excessive con-trast in a space; however, the nonuniformlight reflected from wall or ceiling surfaces isinsufficient to “wash out” all shadow andcontrast. This lack of diffusion yields moder-ate contrast (figure 3.16).

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Figure 3.13 Direct/indirectdistribution. Figure 3.14 An example of direct/indirect distribution.

Figure 3.15 Multidirectional con-centrated (semidirect or semi-indi-rect) distribution. Figure 3.16 An example of multidirectional concentrated distribution.

Vertical Surface IlluminationWall lighting is sometimes a substitute forindirect ceiling lighting: it lightens shadow andreduces excessive contrast. It works espe-cially well when the walls are high in relationto the size of the room. Another substitute isdirect downlights in combination with a light-colored floor: the floor reflects light back tothe ceiling as though indirect lighting werebeing used. The floor must be kept clean forthis technique to be successful.

The ideal lighting arrangement is often acombination of direct and indirect light,where the direct light takes the place of thesun, casting shadows and modeling shapes,and the indirect light softens the shadows,acting as a blue sky or a photographer’s filllight. Direct/indirect lighting designs are pro-duced either with separate systems fordownward and upward light or with onesystem that provides both downward andupward distribution.

SURFACE FINISHES ANDREFLECTANCESWhat is perceived as brightness is not theincident light on a surface, but the light that isreflected from that surface toward the eyes.Brightness results from the intensity of lightthat initially strikes a surface and the reflect-ing or transmitting properties of that surface.

Whether it is of high or low intensity,some amount of incident light from lumi-naires or from interreflection falls on all roomsurfaces. The relative size of these surfacesand the intensity of light reflected from themdetermine their visual prominence in an inte-rior composition.

Reflected light is usually diffuse andmultidirectional, causing interreflectionbetween all surfaces and objects. Thisinterreflection fills in shadows, reduces con-trast, and yields more uniform brightness.

The overall brightness results from thedistribution of reflected light, which, in turn,

depends on the reflectance properties of thesurfaces in the space. Dark-colored, low-reflectance finishes absorb much of the lightthat strikes them, reflecting only a smallamount toward the eye. This gives animpression of a dark, high-contrast spaceregardless of the amount of illuminance (fig-ures 3.17 and 3.18).

Light-colored and high-reflectance fin-ishes reflect much more of the incident light,contributing to a higher brightness and agreater diffusion of light (figures 3.19 and3.20). This interreflection is independent ofthe initial distribution of light, whether thatdistribution is concentrated or diffuse.

The choice of surface finishes augmentsor negates the initial distribution of light fromluminaires. This influence of reflected lightmust be accounted for: understanding therelationship between lighting equipment androom surfaces is critical to successful light-ing design.

Secondary Light SourcesAny object or surface that reflects or trans-mits light becomes a secondary light source.The moon is an example: it is incapable ofproducing light. The moonlight we see is pro-duced by a primary source—the sun—whichis reflected by the moon’s surface.

Similarly, a lighted wall or ceilingbecomes a secondary light source that illu-minates a room through reflection. Theresult is then dependent on the reflectedlight from the lighted surface, rather than onthe initial distribution of light from theluminaires (see color plate 5).

THREE-DIMENSIONAL FORMIn addition to altering our perception ofspace, the direction and distribution of lightaffect the perception of surfaces and objectsin a room.

All three-dimensional form is seen as apattern of brightness contrasts, often con-

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Figures 3.19 and 3.20 If all of the room surfaces are light-colored, interreflections will fill in shadows and reduce contrast.

Figures 3.17 and 3.18 If all the room surfaces are dark, there is little interreflection; contrast is high.

sisting of highlights and shadows. A changein this pattern, caused by a change in thedirection and distribution of light, altersvisual impressions of form and surface.

Lighting alters perception of texture.Grazing light, from luminaires located closeto a surface being lighted, strengthens high-lights and shadows. It enhances the percep-tion of depth by emphasizing the natural

textures and sculptural relief of the surface.Grazing light is also used for inspection todetect surface blemishes and errors in work-manship (figures 3.21 and 3.22).

Grazing light is appropriate for lightingheavily textured surfaces such as rough plas-ter, masonry, or concrete. It is disastrous for“flat” walls of smooth plaster or gypsumboard, however, because such walls are not

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Figures 3.21 and 3.22 Grazing illumination.

Figures 3.23 and 3.24 Diffuse wash light.

truly flat: minor surface imperfections suchas trowel marks, tape, and nail-headdepressions are magnified by the shadowsthat result from grazing light.

Conversely, diffuse wash light reducesthe likelihood that surface flaws will benoticed and strengthens an impression ofsurface smoothness. This is more suitablefor a gypsum board wall or an acoustical tileceiling. Diffuse wash light from the front isparticularly successful at reducing or remov-ing shadows and small variations in bright-ness (figures 3.23 and 3.24).

Concentrated direct lighting on objectsproduces drama and emotional excitement.Yet the same sharp shadows that contributeto the dramatic impact also reduce visibilityof detail. This diminishes the ability to studyand appreciate all aspects of the objectaccurately (figure 3.25).

A diffuse lighting distribution, on theother hand, illuminates the entire object,reducing shadows and facilitating study ofworkmanship and detail. Although it is oftendesirable, this kind of lighting sacrifices the

dramatic impact and visual excitement(figure 3.26).

Sharp highlights and dark shadowscreate a dramatic setting and strengthenimpressions of texture and form; however,they are distracting in a working environ-ment. Some shadows on a work surface aremildly irritating, such as those cast by a handor pencil while one is writing under a concen-trated light source.

Other shadows are extremely distractingand even hazardous, such as those on anassembly line. During a period of sustainedvisual activity, the extreme concentrationand constant reädaptation required by work-ers in high contrast settings result in visualfatigue, errors, and accidents.

Sometimes highlight and shadow aredesirable in a work environment. Just as thehighlights and shadows of a sunny day areemotionally stimulating, carefully placedhighlights and shadows in an interior providevisual relief and interest. Office and factoryworkers benefit from the stimulation andvariation provided by greater brightness con-

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Figure 3.25 Sculpture lighted with concentrated directlighting from below.

Figure 3.26 Sculpture lighted with diffuse lighting fromabove.

trast in corridors, washrooms, lunchrooms,lounges, and other meeting places. On mostwork surfaces, however, diffuse light distri-bution is desirable to minimize highlightsand shadows.

Experience and memory also influenceour perception of objects. Through thecourse of time, people have come to expectmidday sunlight to emanate from a concen-trated source overhead, at an angle lessthan 45° from nadir (straight down), and sky-light to be a diffuse, multidirectional source.

When a lighting system alters theexpected direction of light, it changes thenormal relationship between highlights andshadows. An unnatural impression results,inducing mystery or anxiety (figures 3.27and 3.28).

In practice, objects being exhibited orphotographed are often lighted from two

sides to reduce excessive shadows. One sidehas a concentrated beam-spread to enhancedrama and function as the sun’s directionalrays; the other side receives diffuse illumina-tion to soften shadows and replicate the sky’sdiffusing quality. The background may belighted separately to distinguish the objectfrom its surround and to add visual depth.

GLARE AND SPARKLEExcessive contrast or luminance is distract-ing and annoying. This negative side ofbrightness is called glare. In the extreme,glare cripples vision by reducing or destroy-ing the ability to see accurately.

Glare is often misunderstood as “toomuch light.” In fact, it is light coming from thewrong direction, the result of an extremeluminance within the normal field of view. Thedifference between the high and low beams

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Figure 3.27 Bust of Lincoln lighted from above. Figure 3.28 Bust of Lincoln lighted from below.

of automobile headlights at night demon-strates that glare for the approaching driver isa function of direction as well as intensity. Italso demonstrates that glare may be presentin an environment with little light.

Glare is also a function of luminancearea. Although a small area of luminance istolerable, a larger area of the same intensitybecomes uncomfortable. It is desirable toreduce luminance intensities as the area ofluminance becomes more dominant in thefield of view.

In addition, glare is a function of loca-tion. Within limits, the human eyebrow con-ceals glare from overhead luminaires, butnot from poorly shielded, wall-mountedluminaires or high-luminance wall surfaces,as these elements are directly in the field ofview (figure 3.29).

Direct GlareThe late afternoon sun and an unshieldedelectric light source are examples of the dis-tracting influence of direct glare in the envi-ronment. Direct glare is caused by thelighting system; it is defined as excessivelight misdirected toward the eye.

Usually, the uncontrolled luminance ofan exposed light source produces glare. Forthis reason, bare lamps (the technical wordfor light bulb) are rarely used in architecturalapplications (figure 3.30).

When direct glare occurs in the normalfield of view, three main control techniquesare available. One is to limit the amount oflight emitted in the direction of the eye (figure3.31). Shielding devices such as the hand,used instinctively, and sun visors improve visi-bility and restore visual comfort in this way.

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Figure 3.29 Acceptable luminance valuesdecrease as the source approaches the centerof the visual field.

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Figure 3.30 Unshieldedlamp luminance for equiv-alent light output.

Figure 3.31 Limiting the amount of light emittedtoward the eye.

The second is to increase the area from whichlight is emitted (figure 3.32). A white glassglobe and diffusing panels of white glass orplastic are examples.

The automobile headlights redirectedbelow the line of sight demonstrates thethird technique whereby directional controland change in the direction of the beam(figure 3.33) aid visual comfort. This thirdmethod is more efficient; it uses accuratecontrol devices to redirect light in the desireddirection. Typical devices are reflectors andrefracting lenses that limit the distribution ofstray light emitted toward the eye.

Visual comfort results from the reduc-tion of glare and distracting luminance in thefield of view. Excessive luminance is physio-logically disconcerting and reduces the abil-ity to see detail accurately. The quality andcomfort of vision depend upon the avoid-ance of distracting or disabling luminances.

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Figure 3.32 Increasing the area from which light is emitted.

Figure 3.33 Change in the direction of the beam tocontrol direct glare.

Visual Comfort Probability (VCP)A visual comfort probability (VCP) rating isdefined as the percentage of people who, ifseated in the least desirable location in anoffice work space, will find a lighting installa-tion comfortable. VCP depends on the sizeand shape of the room, the reflectances ofroom surfaces, and the location and lightdistribution of the luminaires.

A VCP of 70 or more is recommendedfor general office use, and 80 or more foroffice areas using video display terminals(VDTs). Originally tested and validated usinglensed fluorescent direct luminaires, VCP isapplicable only for direct lighting systems.

Reflected GlareVisual comfort is achieved by limiting notonly direct glare but also reflected glare.Reflected glare is excessive uncontrolledluminance reflected from objects or surfacesin the field of view. This includes the reflectedluminance from interior surfaces as well asthe luminance of the lighting system.

Specular surfaces have reflecting prop-erties similar to those of a mirror. The lumi-nance reflected is the mirrored image of thelight source, or of another lighted surfacewithin the reflected field of view.

These properties make specular sur-faces useful as reflectors for light control inluminaires, but polished or specular interiorsurfaces such as desks, countertops, floors,walls, and ceilings introduce problems ofreflected glare. Diffuse surfaces preventhighlights and are uniformly bright from allangles of view.

Reflected images on glass and othertransparent materials form a visual barrier.At night, large areas of glass may becomeblack mirrors. If surfaces viewed through thetransparent material are higher in luminancethan the reflected images, a sense of trans-parency is achieved.

Most work surfaces reflect light both dif-fusely and specularly. Diffuse reflectance isdependent on the quantity of illuminance onthe surface. Specular reflectance is depend-ent on the luminance of the source: thereflected image of the lamp or luminaire. Thisreflected image causes a veiling image on thework surface that obscures surface detail.

In the visual task area, remove glossysurfaces wherever possible. A glass-coveredor highly polished desk top is quite specular;reflected images become distracting. Matte(low-gloss) finishes should always be usedfor work surfaces.

It is helpful to think of the work surfaceas a mirror when orienting task luminaires(figure 3.34). Proper luminaire locationreduces reflected glare from the task (figure3.35). When luminaires are located oneither side of the desk, shadows cast by theluminaires are filled in and light is reflectedaway from the worker’s eyes (figure 3.36).

Video Display Terminals (VDTs)VDTs are glossy vertical work surfaces.Screen reflections are caused by variationsin luminance being “seen” by the screen sur-face and reflected into the worker’s eyes.Screens that are convex and inclinedupward, in particular, reflect into the eyeslarge areas of ceiling, walls, windows, andthe surrounding space.

Positioning the screen, adjusting itsangle, low-reflectance screens, blinds on win-dows, and dark clothing for workers are tech-niques that relieve many reflection problems.Reflections caused by the lighting system canbe controlled with properly designed, deep-cell parabolic louvers to prevent lamp imagesfrom appearing on the VDT screen.

In addition to reflections on the screensurface, which make viewing the screenimages difficult, two additional lighting prob-lems that cause concern for VDT users are:(1) proper lighting for the non-VDT tasks the

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worker must also perform, and (2) lighting ofthe area in the worker’s field of view.

Sometimes the ambient room illumi-nance in VDT areas is set low in the beliefthat this improves screen visibility. The oppo-site is true. While low quantities of ambientlight reduce screen reflections, the roomappears visually gloomy; there will also beareas of high contrast between the bright

screen and the dark surround. Furthermore,low ambient illuminance is unstimulating,especially when contact with the outdoorsvia windows is missing.

Indirect uplighting systems are some-times used to avoid luminaire reflections inthe screen. The ceiling must be high enough toallow pendant- or floor-mounted luminaires todistribute light evenly (see figure 13.21) or

40


Figure 3.35

Figure 3.34

excessive contrast is created in a differentway. Even when uniform ceiling luminance isachieved, the diffuse reflected light mayhave a “washing out” effect that reduces thevisibility of the screen. Moreover, because allof the light in the space is diffuse, indirectsystems also create a bland interior.

It is the variation in room luminance thatis extremely critical, however. All surfacesand objects reflected by the VDT screen intothe worker’s normal line of sight—especiallyroom surface finishes such as system dividerpanels, vertical surfaces of filing cabinets,and the ceiling plane—must be of more orless equal luminance if distracting imagesare to be prevented.

Many high-quality VDTs are now fur-nished with integral low-reflectance screens;newer, flat-screen monitors have liquid crys-tal displays (LCDs), which reflect very littlelight from all directions except perpendicularto the screen. In time, VDTs may cease to bea lighting challenge.

SparkleThe principal difference between glare andsparkle is the relationship between the areaand magnitude of luminance in the field ofview. Large areas of luminance are distract-ing and disconcerting; relatively small areasof similar or higher intensity are points ofsparkle and highlight that contribute to emo-tional excitement and visual interest.

• Direct sparkle. Examples include Christ-mas tree lights; small, exposed, clear fila-ment lamps; and perforated shieldingmaterials (see color plate 6).

• Reflected sparkle. Examples includetextured metal and pebbled surface finishes(see color plate 7).

• Transmitted sparkle. Examples includecrystal chandeliers and sandblasted- oretched-glass (frosted) diffusers around clearfilament lamps. Clear filament lamps com-bined with crystal glass, particularly whenthat glass is faceted, introduce subtle color

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Figure 3.36 Proper desk lighting.

highlights via the dispersion of “white” lightinto the rainbow of colors that comprise it(see color plate 8).

The presence of sparkle, highlight, andshadows constitutes the chief visual attrib-

utes that make a sunny day interesting andstimulating; their absence makes a cloudy,overcast day flat and dull. The emotionalstimulation provided by carefully controlledsparkle, highlight, and shadows is equallysignificant in interiors.

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ColorColor is not a physical property of the things we see—it is the consequence of

light waves bouncing off or passing through various objects.

The color of an object or surface is deter-mined by its reflected or transmitted light.Color is not a physical property of the thingswe see—it is the consequence of light wavesbouncing off or passing through variousobjects. What is perceived as color is theresult of materials reflecting or transmittingenergy in particular regions of the visiblespectrum.

Green glass transmits the green portionof the spectrum, absorbing almost all of theother regions; yellow paint reflects the yellowportion, absorbing almost all other wave-lengths (figure 4.1). White or neutral graymaterials reflect all wavelengths in approxi-mately equal amounts.

Pure spectral colors are specified bytheir wavelength, which is usually expressedin nanometers. A nanometer (nm) is one bil-lionth of a meter or about thirty-nine bil-lionths of an inch.

The reflectance chart (color plate 9)shows that butter absorbs blue light andreflects a high percentage of all other colors;these other colors combine to produce whatwe call yellow. Green lettuce reflects lightwith wavelengths primarily in the 500–600-

nm region and absorbs all of the energy atother wavelengths. A tomato is red onlybecause it reflects visible energy at 610 nmwhile absorbing almost all of the other wave-lengths.

A light source that emits radiant energycomparatively balanced in all visible wave-lengths appears “white” in color. Passing anarrow beam of this white light through aprism separates and spreads the individualwavelengths, allowing the eye to distinguishamong them. The resulting visual phenome-non is called a color spectrum (color plate2).

“White” light sources emit energy at allor almost all visible wavelengths, but notalways in an ideal proportion. Almost allsources are deficient at some wavelengthsyet still appear to be white. This deficiencyinfluences the perception of colors; theeffect is known as color rendition. It causesthe graying of some colors while enhancingthe vividness of others.

To provide accurate color perception, alight source must emit those wavelengthsthat a material reflects. Lighting a tomato’ssurface with a white light source makes the

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4

surface appear red, because only red wave-lengths of light are reflected toward the eye.All other wavelengths are absorbed.

If the tomato is lighted with a greensource, however, it will appear dark graybecause no red energy is available to bereflected. The eye can see only the colors ofa surface that are present in the source ofillumination (color plate 10).

Because the proportion of colors in“white” light varies, what we call white lightis a broad category. Within this category, themost common variations are described as“warm” or “cool.” A warm white light empha-sizes the long (high nm) end of the spec-trum, with hues of yellow through orange to

red. Warm light sources that emphasizethese hues include the sun and incandes-cent, tungsten-halogen, and high-pressuresodium lamps. Conversely, a cool white lightsource emphasizes the short (low nm) end ofthe spectrum, with hues of blue throughgreen to yellow. Cool light sources thatemphasize these hues include north skylightand many fluorescent and metal halidelamps.

Spectral distribution charts, availablefrom lamp manufacturers, express the rela-tive color composition of light sources (colorplates 13–17 and 19–31). Because thesecharts are of limited practical value in pre-dicting how colors will appear, simplified sys-

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Figure 4.1 To provide accurate color rendition, the light source must emit the wavelengths that the object reflects.

tems of color notation and color renditionhave been developed.

COLOR TEMPERATUREColor temperature describes how a lampappears when lighted. Color temperature ismeasured in kelvin (K), a scale that starts atabsolute zero (–273°C).

At room temperature, an object such asa bar of steel does not emit light, but if it isheated to a certain point it glows dull red.Instead of a bar of steel, physicists use animaginary object called a blackbody radiator.Similar to a steel bar, the blackbody radiatoremits red light when heated to 800 K; awarm, yellowish “white” at 2800 K; a day-light-like white at 5000 K; a bluish, daylightwhite at 8000 K; and a brilliant blue at60,000 K. The theoretical blackbody is nec-essary because the bar of steel would meltat these higher temperatures.

Color temperature is not a measure ofthe surface temperature of an actual lamp orany of its components. Color temperaturerefers to the absolute temperature of thelaboratory blackbody radiator when its visibleradiation matches the color of the lightsource.

Incandescent lamps closely resembleblackbody radiators in that they emit a contin-uous spectrum of all of the visible colors oflight (color plate 13). Consequently, theincandescent spectrum is accurately speci-fied by color temperature in kelvin. Fluores-cent and high-intensity discharge (HID) lampsproduce a discontinuous spectrum with blankareas punctuated by bands at specific fre-quencies (color plates 14–17 and 19–31).These bands combine to give the impressionof “white” light; fluorescent and HID lampcolor appearance is specified by its apparentor correlated color temperature (CCT).

Incandescent lamps used in architec-tural lighting have color temperatures in the2600 K to 3100 K range; fluorescent lamps

are available with apparent color tempera-tures from 2700 K to 7500 K; north skylightis arbitrarily called 10,400 K.

Unfortunately, the apparent color tem-perature of discontinuous spectrum lightsources fails to provide information about itsspectral energy distribution. For example,warm white and RE-930 fluorescent lampshave the same apparent color temperature,yet their spectral distribution curves andtheir color rendition of objects and materialsare vastly different. This same limitationapplies when using color temperature nota-tions for high-intensity discharge sources,including mercury vapor, metal halide, andhigh-pressure sodium lamps.

COLOR RENDERINGTo remedy this limitation, color renderingexpresses how colors appear under a givenlight source. For example, a shade of red willbe rendered lighter or darker, more crimsonor more orange, depending on the spectral-distribution properties of the light falling on it.

The most accepted method to deter-mine the color-rendering ability of a lightsource is a rating system called the ColorRendering Index (CRI).

The CRI first establishes the real orapparent color temperature of a given lightsource. Then, it establishes a comparisonbetween the color rendition of the given lightsource and of a reference light source. If thecolor temperature of a given source is 5000 Kor less, the reference source is the blackbodyradiator at the nearest color temperature. Ifthe given color temperature is above 5000 K,the reference source is the nearest simulateddaylight source.

The comparison is expressed as an Ra

factor, on a scale of 1 to 100, which indi-cates how closely the given light sourcematches the color-rendering ability of thereference light source. Since the referencefor CRI changes with color temperature, the

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CRIs of different lamps are valid only if theyhave similar correlated color temperatures.Therefore, it is inappropriate to compare twolight sources unless their color temperatureis similar—within 100 K to 300 K.

For example, a 3000 K RE-70 fluores-cent lamp and a 6500 K “daylight” fluores-cent lamp render objects differently, despitethe fact that they both have a CRI of 75. Thisoccurs because the CRI for the 3000 K lampwas compared to a blackbody radiator andthe CRI for the 6500 K lamp was based oncomparison to actual daylight.

Ra is an average of the color renderingability of eight test colors; better performanceat some wavelengths is concealed whenaveraged with poorer performance at otherwavelengths. As a consequence, two lampsthat have the same color temperature andCRI may have different spectral distributionsand may render colored materials differently.

Some typical CRIs appear in table 1 inthe appendix.

The color properties of the light sourcesignificantly alter the appearance of people.Because incandescent sources are rich inred wavelengths, they complement and flat-ter complexions, imparting a healthy, ruddy,or tanned quality to the skin. Cool fluores-cent and HID sources that emphasize theyellow or blue range produce a sallow or paleappearance.

SUBJECTIVE IMPRESSIONSThe color of light has a profound effect onsubjective impressions of the environment.The Amenity Curve indicates that warmerlight is desirable for low luminance values(figure 4.2). It also shows that a room uni-formly lighted to 20 footcandles (fc) will beunpleasant with either kerosene lamps(about 2000 K) or lamps that simulate day-light (about 5000 K).

With the warm-toned kerosene source,the quantity will seem too high and the

space too greatly lighted. With the simulateddaylight source, the same quantity of lightwill seem dark and dingy. Both warm fluores-cent (2700 K or 3000 K) and standardincandescent lamps (2600 K to 3100 K) fallwithin the acceptable range on the chart.

In addition, a warm atmosphere sug-gests friendliness or coziness. A cool atmo-sphere implies efficiency and neatness.Flynn evaluated subjective responses tocolors of white light that are produced byelectric light sources in interior spaces atintermediate illuminance values.

Flynn’s subjects categorized their impres-sions of visually warm versus visually coolspace as follows: cool colors (4100 K) stim-ulate impressions of visual clarity; warmcolors (3000 K) reinforce impressions ofpleasantness, particularly when a feeling ofrelaxation is desirable.

Flynn found that diffuse light plus warm(orange-red) hues intensify impressions oftension and anxiety. Diffuse light plus cool(violet-blue) hues reinforce impressions ofsomberness; at low luminance values, theycreate an impression of gloom.

He also found that patterns of sparkleplus saturated warm (orange-red) huesstrengthen impressions of playfulness andmerriment; this is particularly strong withrandom patterns of light and color. Patternsof sparkle plus saturated cool (violet-blue)hues reinforce impressions of enchantment;this is particularly strong with rhythmic orregimented patterns of light and color.

SURFACE FINISHES AND COLOR OFLIGHTTo reiterate: light does not have color, andobjects do not have color. Color resides inthe eye/brain system.

The relationship between the spectraldistribution of light and the colors of fabrics,walls, and other elements in the interior is,therefore, pivotal. Some objects appear to

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be the same color under a certain lightsource although they are different in spectralcomposition. If the light source is changed,however, the object color differences becomeapparent (color plate 11).

It is advisable to appraise, match, andspecify colored materials using light sourcesidentical in color to those that will be used inthe completed installation. When the lightingsystem that will be installed is unknown, twolight sources of different spectral charactermay be used to examine the samples: one ofthe sources should be predominantly blue in

spectral distribution, such as a daylight fluo-rescent lamp, and the other predominantlyred, such as an incandescent lamp.

Incandescent SourcesIncandescent lamps emit energy in a smoothcurve beginning with a small amount of deep-blue radiation in the near ultraviolet rangeand increasing into the deep-red portion ofthe spectrum (color plate 13). The color ofincandescent light is warm in tone, with mostof the energy concentrated in the red andyellow range. Although this “white” light is

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Figure 4.2 Amenity Curve, based on a pilot study by A. A. Kruithof, 1941.

deficient in blue and green, and tends to graythese colors, it complements the appearanceof warm colors and human faces.

Incandescent lamps enjoy one slightadvantage over other lamps in color render-ing—not because they render colors morenaturally, but because more than a centuryof use has established them as a norm.Incandescent lamps also produce light as aby-product of heat, similar to other sourcesof light that have been familiar for thousandsof years: the sun, open fire, candles, oillamps, and gas lamps. All of these givewarm-colored light and all are point sources.

Good color rendition is usually inter-preted to mean the familiar appearance offamiliar objects: things assume familiarcolors by frequently being seen under certainkinds of light sources, such as incandescentlamps or daylight.

Tungsten-halogen lamps (3000 K) havemore blue and less red energy than standardincandescent lamps; they appear whiterthan the slightly yellowish standard incan-descent lamps (2700 K). All incandescentand tungsten-halogen lamps are assigned aCRI of 100.

Fluorescent SourcesFluorescent lamps produce a discontinuousspectrum: peaks of energy at specific wave-lengths. Variations in the composition of thephosphors that coat the inside of the lampproduce differences in the color of emittedlight. Three principal color temperatures areavailable with fluorescent lamps: (1) warm(3000 K) lamps are compatible with incan-descent lamps, (2) cool (4100 K) lamps arecompatible with daylight, and (3) 3500 Klamps are compatible with both.

Fluorescent lamps also fall into threegroups with regard to efficacy and color ren-dition: standard, deluxe, and rare-earth.Standard white lamps—both cool and warmkinds—produce high efficacy and poor color

rendition (color plates 14 and 16). Warmwhite fluorescent lamps have CRIs of 52 to53; cool white fluorescent lamps have CRIsof 60 to 62.

Deluxe white lamps produce improvedcolor rendering with an approximately 25 per-cent sacrifice in lighting efficacy. The reduc-tion in light quantity is often imperceptible,however, because of the vivid and accuratecolors that improve contrast and portraytones that are grayed with standard lamps(color plates 15 and 17). Deluxe fluorescentlamps have CRIs between 84 and 89.

For both high color rendering and highluminous efficacy, rare-earth lamps are used.Three kinds of rare-earth (RE) lamps areavailable: triphosphor RE-70, triphosphor RE-80, and quad-phosphor RE-90.

Triphosphor rare-earth lamps producelight in accordance with the theory that thehuman eye reacts to three prime colors—blue-violet, pure green, and orange-red(color plate 18). When these three prime(not primary) colors are combined in atriphosphor lamp, only those wavelengthsare emitted; the brain fills in the remainderof the spectrum. This yields more colorfulinteriors because the three narrow-emis-sion, prime-color phosphors compress allhues into the eye’s color response system,increasing color contrast (color plates 19,20, and 21).

Because the eye/brain system can befully stimulated with these three monochro-matic wavelengths, all pigment colors can berendered by adjusting the relative intensitiesof the three prime-color phosphors. The keyis to choose the components that maximizethe visual system responses. For maximumeffect, the three wavelengths must corre-spond to the peak spectral sensitivities ofhuman vision, which are near 450 nm, 530nm, and 610 nm.

RE-70 lamps use a coat of conventionalphosphors and a thin coat of narrow-emis-

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sion, rare-earth phosphors, producing CRIsof 70 to 78. RE-80 lamps use a thick coat ofthe narrow-emission, rare-earth phosphors,producing CRIs of 80 to 86.

Quad-phosphor RE-90 lamps do notuse the narrow-emission phosphors; theycontain four wider-emission phosphors thatproduce CRIs of 95 at 3000 K and 98 at5000 K (color plates 22 and 23). RE-90rare-earth lamps with CRIs of 95 to 98 arethe highest color-rendering fluorescentlamps available.

High-Intensity Discharge (HID)SourcesAs with fluorescent lamps, high-intensity dis-charge (HID) lamps produce a discontinuousspectrum. The different metals in the arc ofthe various HID sources yield different color-rendering abilities.

If you were to throw salt on a barbecue,the sodium chloride would make the flamesappear yellow. Similarly, the sodium in high-pressure sodium lamps makes their colorappear yellow. If you were to throw mercuryon a barbecue, although this is not recom-mended because it would cause mercurypoisoning, the mercury would make theflames appear blue. Similarly, the mercury inmercury vapor lamps makes their colorappear blue.

High-pressure sodium lamps producepredominantly yellow light at 2100 K, whichcreates a shift in how we perceive almost allobserved colors. Reds, greens, blues, andviolets are muted (color plate 24). High-pres-sure sodium lamps have CRIs of 21 and 22.

By further increasing the gas pressureinside the lamp, white high-pressure sodiumlamps produce incandescent-like color at2700 K with good color-rendering propertiesand a CRI of 85 (color plate 25).

Low-pressure sodium lamps emit all vis-ible energy at 589 nm, which means that

they render only materials that reflect light atthat wavelength. All other colors appear gray(color plate 26). Low-pressure sodiumlamps are assigned a CRI of 0.

The clear mercury vapor lamp producesa cool, “white” light of predominantly blueand green energy. The lack of energy at thewarm (red) end of the spectrum results inpoor color rendering; people appear ghastly.Clear mercury vapor lamps exhibit particu-larly poor rendering of red. Rendering ofother colors is fair, but blues appear purplish(color plate 27). Clear mercury vapor lampshave CRIs between 15 and 20.

Applying a phosphor coating to theinside surface of a mercury lamp’s outerbulb slightly improves the color-renderingproperties, but also reduces its efficacy. Thephosphors convert invisible ultravioletenergy into visible light (color plate 28).Phosphor-coated mercury vapor lamps haveCRIs of 45 to 50.

Metal halide lamps are similar in con-struction to mercury vapor lamps, exceptthat various metal halides have been added.These halides add missing wavelengths thatimprove the mercury lamp’s spectral distri-bution, yielding a more uniform spectrumand better color rendering, but reds areslightly muted (color plate 29). The additionof phosphor coatings on the inside of thebulb provides diffusion and some additionalcolor improvement (color plate 30). A broadrange of color-rendering quality exists in thedifferent metal halide lamps; many experi-ence lamp-to-lamp color inconsistency andcolor shift over the lamp life. The majority ofmetal halide lamps have CRIs of 65 to 70.

New ceramic metal halide lamps com-bine the ceramic arc tube technology ofhigh-pressure sodium lamps with existingmetal halide chemistry. The ceramic arctube minimizes color variation betweenlamps and limits color shift during lamp life.

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Because it can withstand higher operatingtemperatures, color rendering is alsoimproved; ceramic metal halide lamps haveCRIs of 81 to 96 (color plate 31). These arethe highest color-rendering HID lamps avail-able.

A “best” lamp color is nonexistent, as is“true” color. Each spectral distributionresults in different object colors, whether

that distribution comes from naturalsources, such as sunlight or skylight, or fromelectric sources, such as incandescent, fluo-rescent, or HID lamps. The “right” colorsource for a given application depends uponan evaluation of trade-offs, including direc-tional control, familiarity, color rendition,efficacy, absence of glare, maintenance,and cost.

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DaylightThe goal of daylight design is to provide visual variety with controlled

brightness contrasts.

A principal characteristic of daylight is itsvariability. The color of daylight changes withthe time of day, the cleanliness of the atmo-sphere, and the interreflection of surround-ing objects. The intensity of the sun changeswith the time of day, the time of year, andthe latitude of the site. The luminance of thesky depends on whether the light is comingfrom an overcast sky, from a clear sky only,or from a clear sky and direct sunlight.

Daylight has two components: sunlightand skylight. Sunlight is the directional beamemitted by the sun; skylight is the diffusereflection of light from particles in the atmo-sphere.

Direct sunlight is usually an impracticalsource for interiors unless it is shielded. Justas electric luminaires are designed to reduceglare, direct sunlight entering interior spacesrequires careful control. For critical seeingtasks, sunlight often causes excessive lumi-nance differences that result in discomfortand poor visibility. This high contrast in thefield of view inhibits the eye’s ability to adjust,leading to visual fatigue and disturbing theaccommodation needed for clear vision.

Skylight, on the other hand, is a usefulsource without shielding. Although special

building configurations or controls are neces-sary to make skylight acceptable forhorizontal tasks at the workplane or for dis-playing art, it is used with less control to lightnoncritical seeing areas such as corridors,stairwells, cafeterias, and seating areas.

People require changing stimuli toremain sensitive and alert. For example,gazing out the window at distant objects pro-vides relief for the muscles of the eye. Andthe constantly changing nature of daylightsatisfies our biological and psychologicalneeds for change—a view of the sky pro-vides information about the time of day,which helps maintaln our biological cycles,and the varying light intensity as a cloudpasses in front of the sun provides respite orstimulation, which helps reduce monotony.

The proper introduction of daylight intothe interior is the simplest way to provide thischange. The goal of daylight design is to pro-vide visual variety with controlled brightnesscontrasts.

Comfort requires moderate changes.Monotony will cause fatigue, but so willoverstimulation. Excessive contrast providesemotional appeal but also impairs visual per-formance. The sudden appearance of a

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beam of sunlight on a task will providemomentary change and relief; if it remains itwill soon cause visual fatigue and stress.

Daylight and view do not necessarily gotogether and often are achieved through dif-ferent building openings. The criteria for pro-ducing a view to the exterior are differentfrom the criteria for producing good interiordaylight.

The more complex the view and themore frequent the changes, the greater willbe our satisfaction. Although large windowsare sometimes desirable, people’s basicneed for a view of the outside can be satis-fied with comparatively small openings.

DAYLIGHT DESIGNWindow size and height above the work sur-face are factors in daylighting design. Ofcourse, as the window becomes larger insize, the amount of daylight increases. Butthe height of the window is the more signifi-cant factor.

The higher the window opening, thedeeper the daylight can penetrate into theroom, and if it is high enough, it may preventexterior brightness from causing glare. This

high-entry light is softened and spread byproper design of the room surfaces.Interreflections between these surfacescause the brightness patterns to becomemore uniform; visibility and seeing comfortare increased.

Windows and other daylight openingsthat are set flush in a wall or ceiling produceexcessive contrasts between exterior bright-ness and the immediately adjacent interiorsurfaces. This contrast is often harsh anduncomfortable.

A softer transition is achieved with theuse of splayed jambs, rounded jambs, anddeep window wells. Instead of the sharpcontrast between adjacent surfaces, thesedesigns provide a zone of intermediate lumi-nance to soften the change (figure 5.1). Thejambs of the window become light-reflectingshelves that reflect the light indirectly intothe interior. Other solutions include usingwhite paint around the windows or hangingdraperies or blinds.

For comfortable seeing, the luminanceratio between fenestration and adjacent sur-faces ought to be less than 20:1. This ratiois also desirable for the surface luminance of

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Figure 5.1 Splayed and rounded window jambs soften contrasts.

luminaires and adjacent surfaces. It is advis-able to limit luminance ratios anywhere inthe field of view to less than 40:1.

Fenestration SectionsWindows placed on a single side of the room(figure 5.2) are the usual method of fenes-tration. To achieve useful work surfaceilluminance throughout the room, limit thedepth of the room to twice the height fromthe floor to a full-room-width window head.For example, if the window head height is10 ft, the optimum room will be no morethan 20 ft deep. Somewhat narrower win-dows provide slightly lower illuminancevalues, but the difference is minor.

This ratio of 1:2 may be increased to 2:5as long as the reflectances of interior sur-faces are high and carefully controlled. If

these ratios are exceeded, people seated inthe deepest part of the room will feel as ifthey are receiving insufficient light, even ifthey are provided with adequate electriclighting.

Windows placed on opposite sidesdouble the feasible room depth fordaylighting. The opposite windows need onlyoccupy the upper part of the wall; the quan-tity of interior light will be almost the same asif the windows were full height, with theadded benefit of reducing the possibility ofglare (figure 5.3).

Skylights are tools for delivering daylightdeep into interior areas of one-story build-ings or into the top floors of multistory build-ings. They also bring daylight into the lowerfloors of multistory buildings through lightwells and reflective devices.

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Figure 5.2 Unilateral section.

Figure 5.3 Bilateral section.

Skylights come in a variety of shapesand sizes. They are made of clear, pat-terned, or translucent glass or various kindsof plastic. Clear, gray-tinted, or milk-whiteacrylics are best for this purpose; their opti-cal properties are similar to glass, and theyare easier to maintain.

Flat skylights have both drainage anddirt-accumulation problems. Domed orslanted skylights mitigate these drawbacks(figure 5.4). Although a domed skylight is“self-cleaning” on the outside, dirt still col-lects on the inside, making a program ofperiodic cleaning as important with skylightsas it is with electric luminaires.

Depending on the shape of the roomand the location and size of the skylight,brightness control will be necessary in areaswith demanding visual requirements. Ifdirectly exposed to view from below, at

angles in the glare zone, skylights oftenproduce excessive luminance and cause dis-abling veiling reflections on tasks. Light fromskylights is controlled with the use of deepwells, splayed wells, and louvers, preventingany view of the skylight at unsuitable anglesand minimizing veiling reflections.

Diffuse (milk-white) plastic or glass sky-lights diminish the biological benefits of day-light by obscuring the view of the weather.Clear glass or plastic skylights, however, pro-duce more heat gain for a given unit ofilluminance at the work surface below andmay admit direct sunlight in undesirable ways.

An exterior shield that shades the skylightfrom direct sun but allows daylight to pene-trate reduces the heat load. For colder cli-mates, double glazing—two thicknesses ofglass or plastic with an air space between—reduces conductive heat loss in winter.

Clerestories have all the attributes ofskylights; because they occur in the verticalrather than the horizontal plane, they can beoriented to prevent the penetration of directsun (figure 5.5). When built in combinationwith a light shelf, a clerestory reflects greatquantities of daylight against the upper ceil-ing yet blocks the view of the glaring sky frombelow (figure 5.6).

When facing the same (or opposite)direction as the main windows, the clere-story extends the room-depth limitations(figure 5.7). When clerestories are locatedon walls opposite each other, as was oftenthe case in early church buildings, these ver-tical glazing sections are called roof monitors(figure 5.8). A series of parallel clerestoriesis suited for large, low-roofed structuressuch as factories and warehouses; this iscalled a sawtooth section (figure 5.9).

To maximize the light delivered by theclerestory, it is recommended that the roofdirectly below the clerestory and the adja-cent interior ceiling area be diffuse andhighly reflective.

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Figure 5.4 Skylight sections.

Tubular skylights deliver natural light to aroom where a traditional skylight or verticalglazing is impractical. They consist of threecomponents: (1) a small, clear acrylic domelocated on the roof, which allows sunlight toenter; (2) an adjustable cylindrical aluminumshaft that has been treated with a highlyreflective coating; and (3) a translucent dif-fuser lens located on the interior ceiling,which disperses light throughout the room(figure 5.10).

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Figure 5.7 Clerestory and main window.

Figure 5.8 Roof monitor section.

Figure 5.9 Sawtooth section.Figure 5.6 Clerestory section with light shelf.

Figure 5.5 Clerestory section.

The dome is typically installed betweenrafters and joists on the roof, and the adjust-able aluminum tube extends from the roof tothe ceiling of the interior. Sold in kits, tubularskylights minimize heat gain and loss: thealuminum tube radiates any collected exte-rior heat into the attic, and the sealed shaftallows very little interior heat to escape up.Also, little UV is transmitted to the interior;almost all of the UV rays are absorbed by thedome, shaft, and diffuser materials.

Heat GainWhen buildings use glazing to admit daylight,a single layer of ordinary glass exposed tothe sun also admits warming radiantenergy—heat. This helps in cold winters butposes a problem in hot summers.

If buildings are properly designed to usedaylight, they reject most of the direct light

from the sun yet still admit an ample supplyof skylight. Just as the sun’s light can becontrolled, there are many ways to controlthe sun’s radiant heat; it may be admitted orexcluded as seasonally required withouteliminating the benefits of daylighting.

Orientation is a primary method formanaging solar heat radiation because thesun strikes differently oriented surfaces withwidely varying intensity. The size and place-ment of glazed areas are also factors in cap-turing the sun’s energy for cold-weather heatgain.

For example, a house benefits if its wallsand roof are oriented to receive heat fromthe sun in the winter and shed it in thesummer. If the principal façade of a housefaces due south or within 30° of due south,the south-facing walls may be designed toabsorb radiation from the low winter sun; theroof may be designed to reject the sun’sheat by reflecting the high summer sun.

It is possible with any building orienta-tion to achieve good quality daylightingindoors. North light is inherently softer,cooler, and more uniform; because of thesun, south light is more intense and variable.But the same high quality of illumination thatcomes naturally from the north sky can beachieved with any other orientation by theproper use of daylight controls.

SHADING DEVICESShading devices used on the inside of thebuilding reflect some of the radiant heatenergy back outdoors, reducing the energygain from the sun by as much as 60 to 70percent. Exterior shading devices can reducethat energy penetration even more—by 90to 95 percent. Exterior shading devices aremore expensive to build and maintain, butwith hot climates or high energy costs orboth, air-conditioning savings often givequick paybacks.

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Figure 5.10 Tubular skylight.

A variety of shading devices areemployed to deliver daylight to where it isneeded and to reduce glare by limitingexcessive luminance in the field of view.Shading devices are divided into two catego-ries: movable and stationary.

Movable controls adjusted in responseto varying sky conditions are the most effi-cient, but they require a human operator oran automatic device. Stationary (static) con-trols are less expensive but are also less effi-cient, because they are unresponsive todaily and seasonal changes.

Movable ControlsDraperies, shades, and screens are avail-able with a wide range of materials that varyin their openness of weave and surfacereflectivity. They provide almost any desireddegree of light transmission or a completeblackout. Greater flexibility is achieved withtwo separately tracked draperies over awindow area—one used to reduce light andthe second to block it completely.

Light-colored venetian blinds (interiorhorizontal louvers) can be adjusted toexclude direct sunshine but reflect light tothe ceiling, increasing its penetration intothe space while still allowing a view of theoutdoors (figure 5.11). Or they can be closedcompletely, blocking both light and view.

But for venetian blinds to functionappropriately under changing sky conditions,they must be operated with an understand-ing of their potential by someone who hasthe opportunity and the incentive to performthe task. Venetian blinds collect dirt easilyand are tedious to clean; they are subject tomechanical failure of support straps andcontrol strings.

Double-glazed windows are availablewith a narrow venetian blind positionedbetween the inner and outer glass, whicheliminates the dirt-collection problem. Theseblinds are fully operable and reject heat

more efficiently than interior blinds or othershading devices such as roller shades ordraperies.

Motorized controls allow convenientadjustment of sun-filtering and light-blockingfabrics on windows and skylights. Theypermit one-touch adjustment of blinds anddraperies for changing activities or changingsun, or they can be programmed to movefabrics with the sun automatically.

Motorized controls may be linked tohome or building automation systems, sothat shades move at preset times or at spe-cific illuminance values. They can also com-bine control of daylight with electric light sothat sun-filtering or light-blocking fabrics andelectric lights are adjusted at the same time.

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Figure 5.11 Properly adjusted venetian blinds reflectdaylight to the ceiling and do not prevent a view outside.

Exterior motorized shades place thesun-filtering fabrics on the exterior of awindow, providing solar protection by stop-ping excessive glare, UV rays, and heatbefore they enter a building. Movable shad-ing devices on building exteriors are difficultto maintain, however, and they deterioraterapidly unless made of a copper alloy orstainless steel. Awnings are highly reliable,but their aesthetic appeal is limited.

Stationary ControlsFixed awnings and building overhangs serveto shade direct sunlight and reduce glarethrough the upper area of windows (figure5.12). They also reduce the daylight enteringthe room, decreasing the illumination closeto the window and the penetration into theroom. The maximum depth of useful lightpenetration is calculated from the outeredge of the awning or overhang instead ofthe vertical plane of the window.

Although they reduce the quantity ofskylight entering the building, overhangs cancollect light from a light-colored exterior sur-round and reflect it into the interior. Thisresults in a more even distribution of light.

An overhang located on the southernside of a building is especially efficient atcontrolling both light and heat from the sun(figure 5.13). In the summer, the overhangshields the glass from the sun’s direct raysyet allows daylight to enter from the lowersky and by reflection from the ground. In thewinter, the overhang allows the low-anglesun to penetrate for warmth, but seatingmust be oriented to avoid direct sun glare.

Exterior horizontal louvers may pick updirect sun, causing excessive luminance anddiscomforting or disabling glare (figure5.14). Exterior or interior vertical louvers areuseful for low sun angles that occur in theearly morning or late afternoon, particularlyon building walls oriented toward the east or

west (figure 5.15). When it is necessary tocontrol both high sun and low sun, “egg-crate” louvers are used because they com-bine horizontal and vertical shielding.

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Figure 5.12 Awning.

Figure 5.13 Overhang.

Direct sunshine from flat skylights or frompitched skylights facing east, south, or westmust also be controlled. Interior louvers ortranslucent shades will reduce glare and heat,but exterior controls provide superior shading.

Exterior sun shades can be oriented toshade light and heat from the sun duringwarm weather yet allow penetration duringthe cold seasons, or be designed to elimi-nate direct sun from the interior all year long(figure 5.16).

A difficulty with fixed overhangs andawnings is that the amount of shading fol-lows the solar seasons rather than the clima-tic seasons. The middle of the summer forthe sun is June 21, but the hottest daysoccur from the end of July to the middle ofAugust. The overhang designed for optimalshading on September 21, when theweather is still warm and solar heat gain isunwelcome, causes the same shading onMarch 21, when temperatures are lower andsolar heat gain is welcome (figure 5.17).

Vegetation, which follows the climaticseasons, provides excellent shading year-round. On March 21, many plants are with-out leaves and do not obstruct the passageof sunlight. On September 21, however, theleaves are still full and provide good shading.Deciduous trees or an overhanging trelliswith a climbing vine that sheds its leaves in

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D A Y L I G H T

Figure 5.15 Vertical louvers.

Figure 5.14 High sun and low sun angles at exteriorlouvers.

winter provide natural climatic control whenplaced in front of south-facing windows.

GLAZING MATERIALSGlazing materials are available with a widerange of heat and light transmittance, color,and prismatic control. Because of its resis-tance to abrasion, glass is the preferredmaterial; where breakage is a concern,acrylic or polycarbonate is substituted. Bothglass and plastic can be tinted in warm, neu-tral, or cool gray tones to reduce the trans-mission of light and heat yet remaintransparent to vision. Saturated colors are tobe avoided except in carefully designed art(“stained”) glass windows.

Translucent glazing materials that trans-mit diffused light but obscure vision includeetched, sandblasted, opal, and patternedglass and plastic. Many translucent materi-als become excessively glary with exposureto the sun and will be distracting when seenfrom task areas. Because they prevent aview of the outside, their psychological valueis minimal. As diffusion increases so doesthe area of luminance and the possibilitythat the window or skylight will become asource of glare.

Selectively transmitting materials allowthe desirable wavelengths of the visible

spectrum to pass but reflect or absorb theradiant heat energy. Directionally selectiveglass blocks and prismatic glass or plasticsrefract light for directional control.

When installed vertically, prismatic glassblock walls are used to reflect daylight ontothe ceiling of a room, increasing illuminancevalues deep in the interior and removing theglaring sky from view (figure 5.18). Wheninstalled horizontally, as with glass-blockpavers, they transmit light yet maintain a lowsurface luminance even when exposed todirect sun.

QUANTITYBecause of the great variety of changing sunand sky conditions, it is impractical to pre-dict precisely the interior illuminance pat-terns derived from daylighting. By knowingthe size and position of windows and usingtables of average daylighting conditions forvarious locations and orientations, the aver-age amount of available daylight that willenter a space can be determined, but notthe precise amount at any moment.

Interior daylight illuminance values areoften expressed as a daylight factor. Thedaylight factor accounts for light receiveddirectly from the sky, light reflected fromexternal surfaces, and interreflections within

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Figure 5.16 Skylight shades.

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D A Y L I G H T

Figure 5.17 Shading a south window with a fixed overhang (at solar noon).

the room. It is a measure of the proportion ofthe outdoor illumination to the daylight illu-mination received indoors.

Average interior daylight illuminance isalso calculated by graphic methods, such asthe Libbey-Owens-Ford™ “Sun Angle Calcu-lator,” and by computer programs that con-sider geographic location, time of day, time ofyear, fenestration, room shape, and interiorfinishes. The most sophisticated programsproduce a rendering of the interior showingthe relative luminances of room surfaces.

The simplest, most versatile, and mostreliable technique for studying the aestheticsof daylighting is simulation by construction ofa scale model. Daylight behaves in the sameway in a scale model as in an actual building.If studied under similar sky conditions, theinterior of the scale model appears exactly aswill the interior of the building. Miniaturephoto electric cells are placed inside themodel to read illuminance values. But identi-

cal sky conditions are difficult to achieve byplacing the model outdoors; this has led tothe development of sky simulators that canreproduce almost any sky condition.

ENERGY CONTROLPhotosensors (light-sensing devices) auto-matically switch electric luminaires off whenthe daylight contribution at selected interiorlocations reaches prescribed levels. Theluminaires are automatically switched on asthe available daylight decreases. This kind ofswitching has the disadvantage of callingundue attention to the change; it may beabrupt and jarring.

Dimming systems that allow a gradualincrease and decrease in light quantity aremore satisfactory. This is more pleasant andmay even go unnoticed. Sophisticated sys-tems are designed with a built-in delay sothat a cloud passing rapidly across the suntriggers no response.

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Figure 5.18 Prismatic glass block directs daylight toward the ceiling.

6Incandescent LampsThe incandescent lamp is a simple device—a hot wire (the filament) sealed in a

glass jar (the bulb).

An electric current passing through the wireheats it to incandescence, and the wire emitslight. The filament wire diameter and lengthdetermine the amount of electrical currentdrawn by the lamp, regulating its light output(figure 6.1).

The incandescent lamps discussed inthis chapter are commonly referred to as“large” lamps. This designation does notrefer to large physical size, but has tradition-ally described lamps that operate on stan-dard-voltage circuits. The “large lamp”category now includes lamps of many volt-ages commonly found in residential, com-mercial, and industrial use.

“Miniature” lamps, conversely, are notnecessarily small, although many of themare. They are lamps that operate at lesscommon voltages, powered by storage bat-teries or by transformers that reduce orincrease the standard voltage to the voltagerequired by the lamp. Their predominant useis in transportation vehicles and instruments.

The family of large lamps contains aboutone hundred combinations of glass andquartz bulb shapes and sizes. These varia-tions are designated by a two-part abbrevia-

tion: the first part, one or more letters, indi-cates the shape of the bulb; the second part,a number, indicates the diameter of the bulbin eighths of an inch. For example, an A19lamp is an arbitrary-shaped lamp that is 19

8

(238) inches in diameter (figure 6.2).

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Figure 6.1 Incandescent lamp components.

A arbitrary (with familiar teardrop shape)AR aluminum reflectorB flame (smooth)C cone shapeCA candleF flame (irregular)G globe shapeGT globe–tubularMR multifaceted mirror-reflectorP pear shapePAR parabolic aluminized reflectorPS pear–straight neckR reflectorS straight sideT tubular

LAMP BASESIncandescent lamps have a base at one end,although some tubular lamps have bases atboth ends. All bases conduct current fromthe electrical supply into the lamp (figure6.3); most bases also support the lampphysically, but many kinds of PAR lamps canbe supported by their bulbs.

The most frequently used is the mediumbase; its name describes its size. Smallerlamps have smaller bases, including bayo-net, bipin, candelabra, intermediate, minia-ture, mini-candelabra (“mini-can”), twist-and-lock (TAL), and two-pin bases. Largerlamps have larger bases, including mogulscrew and medium and mogul bipost bases.The bipin and bipost bases orient the fila-ment position, providing rotational align-ment for optical control. Bayonet andprefocus medium and mogul bases alsolocate the filament in the exact predeter-mined position required for optical instru-ments and searchlights.

FILAMENTSAll incandescent lamps contain a filament,which is more or less centered within thebulb. A filament is a length of tungsten wire;tungsten is used because of its high melting

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65

Figure 6.2 Incandescent bulb shapes at one-half actual size.

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67

I N C A N D E S C E N T L A M P S

Figure 6.3 Incandescent lamp bases at one-half actual size. The arrow indicates the point from which the light centerlength (LCL)—the dimension from the filament to a designated point that varies with different base types—is measured.

temperature. Occasionally the wire is straight,but usually it is coiled to pack more lengthinto a small envelope, concentrating lightand heat and increasing efficacy. Coiled fila-ments are designated by the letter C. Some-times the coil itself is coiled and designatedCC for “coiled coil.”

Filament design is determined by strik-ing a balance between light output and lamplife. It is a function of filament temperature:the higher the temperature at which the fila-ment operates or “burns,” the more light itemits and the shorter its life—the sooner itfails or “burns out.” A long-life lamp of agiven wattage produces less light than astandard-life lamp of the same wattage,which consumes the same current but isdesigned for a shorter life.

Lamp efficacy is the ratio of light pro-duced (measured in lumens [lm]) to electric-ity consumed (measured in watts [W]). Lamplife is measured in hours (hr).

LIGHT OUTPUTLamp bulbs do not contain air, because theincandescent tungsten will react with theoxygen in the air and quickly evaporate.Originally this was prevented by creating avacuum in the bulb. Today, filling the bulbwith an inert gas slows bulb blackening,which is caused by condensation of evapo-rated tungsten particles on the inner bulbwall. Argon, nitrogen, and krypton gases areused for this purpose. (Some incandescentlamps, particularly those below 40 W, stilluse a vacuum.)

Although reduced by the inert gas pres-sure, the filament evaporation continuesthroughout life; the tungsten wire becomesthinner, consumes less power, and emitsless light. This light loss combined with bulbblackening causes a steady decrease in lightoutput throughout the life of the lamp.

A reciprocal relationship exists betweenlight output and life. Over-voltage operationresults in higher wattage, higher efficacy,and higher light output, but shorter lamp life.Under-voltage burning results in lower watt-age, lower efficacy, and lower light output,but longer lamp life (figure 6.4). As a rule ofthumb, a given percentage reduction inwattage is accompanied by double that per-centage reduction in light.

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Figure 6.4 Incandescent lamp characteristics asaffected by voltage (V). For example, operating a 120 Vlamp at 125 V means approximately 16% more light(lm), 7% more power (W), and 42% less life (hr). Oper-ating a 120 V lamp at 115 V means approximately 15%less light (lm), 7% less power (W), and 72% more life(hr).

Incandescent lamps are usually sold bywattage, but a watt is not a measure oflight—it is a measure of power consumed.With electric light sources, it is a measure ofhow much electricity the lamp uses duringoperation. Lumens tell how much light alamp emits.

Extended-service (2,500-hr) incandes-cent lamps achieve their longer life by areduction in light output and efficacy. Lumenoutput is approximately 15 percent less thanstandard 750-hr and 1,000-hr life lamps.These lamps are more expensive than stan-dard ones, but their longer life is useful inlocations that are difficult to relamp.

Many energy-saving or “watt-saving”lamps are simply reduced-wattage lamps.The reduced power consumption is accom-plished by a reduction in light output. Someenergy-saving lamps have a more efficientfilament design, gas fill, or reflector bulbshape to maintain light output.

LAMP TYPESIncandescent lamps are divided into threecategories according to their ability to directlight: (1) nondirectional sources emit light inall directions and require additional compo-nents to control their distribution, (2) semi-directional sources give a direction to theirlight output and require additional compo-nents to complete a spatial distribution, and(3) directional sources control the distribu-tion of emitted light and require no addi-tional components, being complete opticalsystems in themselves.

Nondirectional SourcesNondirectional lamps emit light in all direc-tions. They include A, C, G, P, PS, S, and Tshapes and decorative lamps. These lampsrequire external elements in the form of alens, reflector, or shield to modify their distri-bution and to control their brightness (figure6.5).

To reduce the glare from an exposed fil-ament, many nondirectional lamps have acoating applied to the inner surface of theclear bulb. A two-bath acid etch or a lightcoating of electrostatically applied whitepowder absorbs an insignificant amount oflight, yielding a ball of light inside the bulb.This kind of lamp has lower luminance andless glare than the exposed filament. It iscalled an inside-frost lamp (figure 6.6).

Still greater diffusion, with a furtherreduction of glare and a sacrifice of about 2percent of the light output, is achieved by adouble coating of white silica powder. Thisgives a ball of light the size of the lamp, yield-ing a bulb of almost uniform brightness. It iscalled a soft-white lamp.

In both treatments, the outer surface ofthe bulb is left smooth, which makes it easyto clean. Inside-frost lamps are preferred formost luminaires to reduce the sharpness ofshadows and the possibility of striations onnearby surfaces. Where the small pointsource contributes to glitter, as in the spar-kle of crystal chandeliers, clear lamps arenecessary.

Semi-Directional SourcesThe category of semi-directional sourcesincludes silver-bowl and white-bowl lamps.Silver-bowl lamps, usually used to direct lightupward, have an opaque silver coatingapplied to the inside of the bowl (figure 6.7).This functions as a specular reflector thatremains clean, and therefore efficient,throughout the life of the lamp. Silver-bowllamps are available in both clear and insidefrost.

When used indirectly in a suspendedluminaire to light the ceiling, the upper partof the bulb must be concealed to preventexcessive brightness and glare. This isaccomplished by an assemblage of circularrings around the lamps or by a shallow, dif-fusing glass bowl. When silver-bowl lamps

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70


Figure 6.5 A-shape lamps at one-half actual size. Maximum Overall Length (MOL): maximum end-to-end length of thebulb within tolerances stipulated by the American National Standards Institute (ANSI). Actual length may be less. Lightcenter length (LCL): the distance from the center of the filament to a designated point that varies with different base types.

are used in recessed luminaires, the upwardlight emitted by the lamp is redirected in adownward direction by a secondary reflector.

White-bowl lamps, also used for indirectlighting, have a translucent white coating onthe inner surface of the bulb bowl, whichreduces the direct filament glare. As withsilver-bowl lamps, white-bowl lamps requireadditional control elements.

Directional SourcesDirectional sources are lamps that are com-plete optical systems; they include a source(the filament), a reflector, and sometimes alens or a filament shield. Lamps in this cate-gory are reflector (R), aluminum reflector(AR), multifaceted mirror-reflector (MR), andparabolic aluminized reflector (PAR). Thesedirectional sources are available in a widerange of wattages and beam-spreads, asindicated in table 2 in the Appendix.

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Figure 6.6 Clear, inside-frosted (acid-etched), and soft-white (silica-coated) lamps.

Figure 6.7 Silver-bowl lamp.

R lampsIn reflector (R) lamps, the bulb is shaped intoa reflecting contour; the inner surface iscoated with vaporized silver. The lamps areavailable in spot or flood beam-spreads.Spot lamps have a light frost on the insidefront of the bulb; flood lamps have a heavierfrosting to increase the spread of the beam.

As with nondirectional and semi-direc-tional incandescent lamps, the glass bulbsof most R lamps are made of blown limeglass. This “soft” glass is intended only forindoor use. Some wattages are available in a“hard,” heat-resistant glass for areas wherecontact with moisture is a possibility, butthese lamps still require protection fromrain.

All R lamps emit a substantial percent-age of light outside the principal beam.Unless intercepted by an auxiliary reflector,this light is usually lost due to absorptionwithin the luminaire; in most luminaires, Rlamps are inefficient.

AR and MR lampsSee low-voltage lamps, pages 75 to 77.

PAR lampsParabolic aluminized reflector (PAR) lampsare made of low-expansion, heat-resistantborosilicate glass that is pressed rather thanblown. This method of construction allowsgreat precision in shaping the reflector of thebulb and in the configuration of the lens, aswell as in the positioning of the filament. Thecombined precision of these factorsaccounts for the superior beam control andgreater efficacy that are characteristic ofPAR lamps (figure 6.8).

PAR lamps were originally designed foroutdoor applications and are sometimes stillreferred to as “outdoor” lamps because theyare weather-resistant. Over the years theiruse indoors has grown rapidly wherever effi-cacy and precise beam control are desired.

PAR lamps are available with beam-spreads that range from 3° (very narrowspot, or VNSP) to 60° (very wide flood, orVWFL). The initial beam is formed by theshape of the reflector and the position of thefilament. The configuration of the lens modi-fies that beam: a light stipple smoothes thenarrow beam for a spot lamp; “prescription”lenses similar to those of car headlights pro-vide the wider beam distributions of floodlamps.

In cool-beam PAR lamps, a reflectivedichroic coating replaces the bright alumi-num used on the reflector surface of stan-dard PAR lamps. Visible wavelengths (light)are reflected forward into the beam whileinfrared wavelengths (heat) pass through theback of the bulb. About two-thirds of theheat energy in the beam is removed; lightoutput and distribution are unchanged.These lamps were originally developed tolight perishable foods (figure 6.9).

EPACTThe U.S. Energy Policy Act of 1992 (EPACT)established minimum average efficacy stan-dards for certain incandescent R and PARlamps that operate at 115 to 130 V andhave medium bases and diameters largerthan 2¾ in. Most incandescent R30, R40,and PAR38 lamps do not meet the criteria;tungsten-halogen PAR lamps do. Coloredlamps and rough- and vibration-servicelamps are exempt from the efficacy stan-dards. The act does not prescribe standardsfor other kinds of incandescent lamps.

As of 31 October 1995, the followinglamps are prohibited from manufacture orsale in the United States: 75R30; 75-, 100-,120-, and 150R40; and 65-, 75-, 85-, 120-,and 150PAR38. These efficacy standards,measured in lumens per watt, were estab-lished according to lamp wattage. Thisapproach ignores the function of theluminaire, however: an inefficient, incandes-

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cent R lamp with a well-designed reflectorcan be more efficacious than the most effi-cient, tungsten-halogen PAR lamp in a light-wasting, multi-groove-baffle downlight.

TUNGSTEN-HALOGEN LAMPSThe tungsten-halogen (or halogen) lamp isan incandescent lamp with a selected gas ofthe halogen family sealed into it. As the lamp

burns, the halogen gas combines with tung-sten molecules that sputter off the filamentand deposits the tungsten back on the fila-ment, rather than on the bulb wall. Thiskeeps the bulb wall clean and at the sametime builds up the filament wire to compen-sate for the evaporative loss that reduces itsdiameter, thus maintaining relatively con-stant wattage. The result is a lamp that deliv-

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Figure 6.8 R and PAR spot and flood lamp beam-spreads.

ers almost its full light output throughout itslife (figure 6.10).

In order for this self-cleaning cycle tooccur consistently, the temperature of thelamp bulb must be a minimum of 500°C.The use of quartz rather than glass is dic-tated by this thermal requirement and theneed for strength to resist high internal gaspressures. Although quartz is no longer theonly material used for the enclosure of these

lamps, the lamps are still sometimes referredto as “quartz-halogen.”

The high internal pressure may cause anexplosive shattering of the bulb if it developsa fault and fails. Although this is a rareoccurrence, halogen lamps must beenclosed because fragments of quartz glassare hot and can cause burns or start a fire.The halogen tube is either enclosed in anouter bulb or used in a luminaire equippedwith a glass cover or fine mesh screen.

The higher the operating temperature ofa filament, the higher the color temperature.Therefore, halogen lamps have a higher colortemperature than conventional incandescentlamps. And, greater energy in the blue regionof the spectrum makes them appear“whiter.” They have longer life and greaterefficacy; they are also more compact, permit-ting the use of smaller luminaires.

Halogen lamps are available in five con-figurations: (1) single-ended T; (2) double-ended T; (3) integral-reflector AR, MR, andPAR; (4) modified A-lamp CP, MB, and TB;and (5) modified decorative B and F shapes.

Single-ended halogen lamps have bayo-net, bipin, miniature screw, mini-candelabra(“mini-can”), twist-and-lock (TAL), or two-pin bases in sizes that range from T3 to T24and wattages from 5 W to 10,000 W.

Double-ended halogen lamps haverecessed single contact (RSC) bases, one at

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Figure 6.9 Cool-beam PAR lamp. Since the unwantedheat is transmitted from the back of the lamp, cool-beamlamps are to be used only in luminaires designed to allowthe heat to escape.

Figure 6.10 Halogen cleaning cycle.

each end of the lamp. Their bulbs are ofsmall diameter: T2, T2½, T3, T4, T6, and T8.Wattages range from 45 W to 2,000 W.

Halogen Infrared (IR) Lamps0f the energy radiated by standard incandes-cent and halogen lamps, 85 percent is invis-ible infrared (heat). Infrared reflecting (IR)halogen lamps have a thin, infrared-reflec-tive coating applied to the inner filamenttube that converts some of the infraredenergy to visible light. The coating allows vis-ible light to pass through the tube wall; theinfrared energy is reflected back onto thelamp filament, further heating the filamentand producing more visible light for the sameamount of energy.

The operating temperature for the halo-gen cycle is maintained with less inputpower, resulting in increased efficacy: theefficacy of a standard 1750 lm, 100 W, A-lamp is 17.5 lm/W; conventional halogenlamps have efficacies of approximately 20lm/W; halogen IR lamps have efficacies inexcess of 30 lm/W.

LOW-VOLTAGE LAMPSLow-voltage lamps are not of magical con-struction—they are simply incandescentand tungsten-halogen lamps that operatebetween 6 V and 75 V.

The wattage of all filament lamps is theproduct of the voltage delivered at thesocket multiplied by the amperes (current)flowing through the filament. The lower thevoltage of the lamp of a given wattage, thehigher the amperes and the larger the diam-eter of the filament wire required to carry it.

The increased diameter of the filamentwire of low-voltage lamps allows for a morecompact filament. The more compact the fil-ament, the more precise the beam control.The main advantage of low-voltage lamps istheir precise beam control.

An increase in the diameter of a filamentwire raises the temperature at which it canbe operated without danger of excessiveevaporation. High-wattage lamps, therefore,are more efficacious than low-wattagelamps of the same voltage and life rating.Lower-voltage lamps, because their filamentwire is of greater diameter, are also moreefficient than higher-voltage lamps of thesame wattage; thus, a 120 V lamp (commonin the United States and Canada) is moreefficacious than the 250 V lamps used inmuch of the rest of the world.

Low-voltage reflector lamps with narrowbeam-spreads are energy-saving when theirconcentrated distribution is used to lightsmall objects or large objects at great dis-tances because light is confined to thelighted object without spilling beyond it.Where wider beams are required, low-volt-age lamps are often less efficient than stan-dard lamps.

Low-voltage operation also means thatthe standard building current of 115 V to125 V must be stepped down by the use of atransformer. Low-voltage luminaires withintegral transformers are often larger, bulk-ier, and more expensive than line-voltageequipment.

The low-voltage lamps commonly usedfor architectural applications operate at 12V. They include PAR, AR, and MR lamps.Low-voltage PAR lamps are manufactured inthe same way as line-voltage PAR lamps; theshape and diameter of the lamps may differ,and the bases are always different to avoidwrong electrical connection (figure 6.11).

Many low-voltage PAR lamps areequipped with filament shields to minimizethe stray light that comes directly from thefilament. As a result, the lamps emit only thecontrolled beam from the reflector. These fil-ament shields have the added benefit of pro-viding glare control by preventing view of thefilament.

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The aluminum reflector (AR) lamp con-sists of a prefocused axial filament lamp andfaceted aluminum reflector that form anoptical system. With some AR lamps the fila-ment cap forms a grip for easy handling inaddition to preventing direct glare from view.Other AR lamps have an integral diffusingglass lens to modify the beam-spread.

AR lamps are available without lenses indiameters of 70 mm and 111 mm (figure6.12) and with lenses in diameters of 37mm and 56 mm. The AR111 lamp is compa-rable to the PAR36 lamp size and base andis used interchangeably with sealed-beam

PAR36 lamps. AR111 lamps also haveexcellently designed reflector surfaces.

With multifaceted mirror-reflector (MR)lamps, a small halogen lamp is attached to amirror with a surface composed of specularfacets (flood) or a smooth plane (spot)(figure 6.13). The mirror is ellipsoidal inshape; the lamp’s coiled filament is placednear its focus.

This combination acts as an optical con-densing system in slide projectors, removingthe need for lenses to control the light pat-tern. By changing the shape of the mirror orrelocating the light source within the reflec-

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Figure 6.11 Low-voltage PAR36 and low-voltage PAR56 lamps at one-halfactual size.

tor, MR lamps are produced with beam-spreads from 7° (very narrow spot) to 60°(wide flood).

MR lamps are available in both 138 in

(MR11) and 2 in (MR16) diameters witheither a miniature two-pin or turn-and-lock(50 W only) base. MR11 lamps are offeredin 12 W, 20 W, and 35 W versions. MR16lamps are offered in 20 W, 35 W, 42 W, 50W, 65 W, 71 W, and 75 W versions. MR16IR (infrared-reflecting) lamps are available in20 W, 35 W, 37 W, 45 W, and 50 W ver-sions.

Originally all MR11 and MR16 lampshad glass bulbs, two-pin bases, open fronts,and dichroic reflector coatings. These coat-ings remove two-thirds of the infrared heatfrom the projected beam and pass it throughthe back of the lamp, with the advantagesdescribed earlier for dichroic PAR38 cool-beam lamps.

The compact size of these lamps encour-aged the design of compact luminaires. Thisoften caused severe problems of heat build-up, however, because heat that is usuallyradiated from the front of a directional lampnow passes through the back and into theluminaire. To correct this problem, lampmanufacturers developed some MR11 andMR16 lamps with an aluminum-reflectorcoating that substitutes for the dichroiccoating. This aluminum reflector coatingalso prevents “spill” light from the back ofthe lamp.

MR lamps are also available with a glasscover on the front of the lamp to protectagainst shattering of the halogen tube and,in some cases, to spread and smooth thebeam. Other variations include reflectorsmade of aluminum instead of glass and turn-and-lock bases instead of the two-pin bases.Lamps with improved dichroic coatings pro-vide constant color over lamp life, longerlamp life, and improved lumen mainte-nance.

COLORED LIGHTColored light is commonly described in termsof hue, saturation, and brightness. Hue isthe quality that is called red or green. Satu-ration is the strength or depth of the color—the amount by which the light appears todiffer from white. A deep red light, for exam-ple, is said to be of high saturation; pink is ared of low saturation. Brightness is the per-ceived quantity of light, without regard tohue or saturation.

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Figure 6.12 AR70 and AR111 lamps at one-half actualsize.

Figure 6.13 MR11 and MR16 lamps at one-half actualsize.

A colored or filtered incandescent lampproduces colored light by starting with“white” light and filtering out the undesiredportions of the spectrum. Yet most coloredlight sources, even those that appear highlysaturated, are not truly monochromatic.They emit a fairly wide band of wavelengths,often including small amounts of energy inother hue regions. The less saturated thecolor, the greater the content of other hues.

Color FiltersThe predominant method of producing col-ored light is the use of color filters with a“white” light source. The white source con-tains all of the colors of the spectrum; thefilter absorbs the unwanted parts of thespectrum and transmits the wavelengthsthat make up the desired color.

Color filters are usually designed forincandescent lamps. Other types of lightsources, lacking a truly continuous spec-trum, are seldom used with color filters. Thegreatest use of colored light is in retail storewindows and in theatre, television, and pho-tographic lighting.

Gelatin filters (“gels”) are thin, colored,transparent plastic sheets available in a widevariety of colors as well as multicolored anddiffusing sheets. Deeper saturations areobtained by using more than one thickness.Gels have a short service life because theircolor fades rapidly when they are transmit-ting intense light and heat.

Colored plastic panels are available foruse with fluorescent lamps but are unsatis-factory for use with hot incandescent fila-ments. Colored glass filters, which canwithstand the heat of incandescent lamps,come smooth, stippled, prismatic, or split;they are highly stable.

Interference filters consist of one ormore layers of ultrathin film coating on clearglass that reflect rather than absorb theunwanted wavelengths. The number and

thickness of the film coatings determine thetransmission (hue and saturation). Becauseunwanted wavelengths are not absorbed,interference filters remain cool.

Some interference filters are designedto reflect or transmit a portion of the spec-trum: infrared or ultraviolet or both. Broad-band interference filters are often calleddichroic (“two-colored”) because they trans-mit one color and reflect the complimentarycolor (figure 6.14).

It is advisable to determine the approxi-mate spectral composition of the “white”light source before selecting a filter. If thedesired wavelengths are not present in theoriginal source, the filter will be ineffective.An extreme example is a red lamp with agreen filter, which will transmit no visiblelight.

Colored LampsIncandescent colored sign and decorativelamps have outside ceramic enamels,sprayed finishes, or dip coatings applied toclear bulbs to obtain colored light by thesubtractive method: by absorbing the light ofthose colors that are undesirable.

Transparent ceramic enamels are usedto coat clear glass bulbs; the finely groundcolored glass is fired into the bulb to fuse thecoating into a hard, permanent finish. Thecoating is applied before the bulbs are madeinto lamps. This makes these lamps resis-tant to scuffing, chipping, and weather, butthey are less transparent than lamps withlacquers or plastic coatings.

Sprayed finishes, usually shellacs or sili-cones, are applied to the completed lamp.Although these sprayed coatings have goodadhesion, they lack the hardness of theceramic enamels and have less resistanceto scratches or scuffing. Sprayed lacquersare highly transparent and therefore oftenused when the sparkle of a visible filament isdesired.

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Dip coatings of transparent colors thatare given an overcoat of acrylic are animprovement over the sprayed lacquers;they yield a similar result with a higher resis-tance to abrasion and weather. These plas-tic-coated lamps offer more sparkle, greaterbrightness, and higher saturation for anygiven color.

Colored 50R20, 75R30, and 150R40lamps are manufactured with fired enamelfinishes. Colored 100PAR38 lamps have acoating of dye-impregnated silicone plastic,similar to the plastic-coated sign lamps.

Colored 150PAR38 lamps have dichroicinterference filters that are vacuum-depos-ited on the inside of the cover lens. The filter

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Figure 6.14 Interference (dichroic) filter.

produces its specific color by transmittingonly the desired wavelengths of light, withminimal heat absorption; light of other wave-lengths is reflected back into the lamp. It is

often more efficient than passing lightthrough color-absorbing materials, and itproduces a more brilliant color than absorp-tion methods.

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Discharge LampsIn electric discharge lamps, light is produced by the passage of an electric

current through a vapor or gas, rather than through a tungsten wire as in

incandescent lamps.

The light production by discharge sources ismore efficient than the electric heatingmethod used in filament lamps. Dischargelamps used in architectural lighting are moreefficacious and have a longer life. See table4 in the Appendix.

FLUORESCENT LAMPSA fluorescent lamp is a low-pressure mercuryarc discharge source. Its operation relies onan electrical arc passing between two cath-odes, one at either end of a glass tube. Fluo-rescent lamps require a ballast to providethe proper starting voltage and regulate thelamp operating current.

When the voltage difference between thetwo cathodes is sufficient to strike an arc, anelectric current passes through mercury vaporwithin the bulb. As the arc current passesthrough the vapor, it causes changes in theenergy levels of electrons in the individualmercury ions. As the electrons change levels,they release several wavelengths of visibleand ultraviolet energy. This radiation strikesthe tube wall, where it causes phosphormaterial to fluoresce (become luminous) andemit light (figure 7.1).

Because light emanates from the phos-phor, light from a fluorescent lamp is emit-ted from the surface of the bulb; the entiretube is the actual light source. Average lumi-nance of the lamp is comparatively lowbecause light is generated from a large area.See table 5 in the Appendix.

The selection of phosphors and addi-tives determines the kind of light that is pro-duced: ultraviolet light, colored light, or themore commonly numerous variations of“white” light.

Although operating principles are thesame for all fluorescent lamps, two kinds ofcathode exist: hot-cathode and cold-cath-ode. (These names are misleading, however,because the cold-cathode type dissipatesmore heat than the hot-cathode kind.)

Cold-CathodeThe cold-cathode lamp is a thimble-shapedcylinder of soft iron, sometimes coated withemissive materials (figure 7.2). This large-area source of electrons has an extremelylong life. Voltage drop at the cathode is higherthan with a hot cathode; therefore, the watt-

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7

age loss is greater, more heat is developed,and lamp efficacy is lower.

Neon is a particular kind of small-diame-ter, cold-cathode lamp; it is easily bent toform signs and artworks. The operating prin-ciple is related to that of other cold-cathodelamps, but light is produced by excitation ofthe gas itself without the help of phosphors.All cold-cathode lamps provide instant start-ing and are easily dimmed.

Although lower in efficacy and output,cold-cathode lamps have a longer life. Theyare used for decorative applications and inplaces where inaccessibility makes lampreplacement difficult. Cold-cathode lampsare less frequently used than the hot-cath-ode kind.

Hot-CathodeHot-cathode lamps are used for virtually all flu-orescent lighting. The cathode is a coiled tung-sten filament at each end of the bulbimpregnated with electron-emissive materials.Hot-cathode lamps are operated at a higherlight output per unit length and with a higheroverall efficacy than cold-cathode lamps,resulting in a lower cost for equal illuminance.

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Figure 7.1 The fluorescent (hot-cathode) lamp consists of a glass tube, internally coated with phosphors that convertultraviolet energy into light; cathodes supported by a glass structure and sealed at the ends of the tube; a filling gas to aidstarting and operation—usually a combination of krypton, argon, and neon; a small amount of mercury, which vaporizesduring lamp operation; and a base cemented on each end of the tube to connect the lamp to the lighting circuit.

Figure 7.2 Cold-cathode lamp.

The superior efficacy and greater lightoutput make the hot-cathode (“fluorescent”)lamp more suitable in almost all lightingapplications; hot cathode lamps are the prin-cipal light source for lighting building interiors.Fluorescent lamps are usually identified by an“F” followed by wattage, shape, bulb diame-ter in eighths of an inch, and color (phosphorkind and correlated color temperature). Forexample, F32T8/RE830 is a 32 W, 1-in-

diameter, fluorescent lamp with rare-earthphosphors and a correlated color tempera-ture of 3000 K (figure 7.3).

Lamp-ballast circuitsFluorescent lamps require a ballast to regu-late the electric current through the lamp.Three kinds of fluorescent lamp-ballast cir-cuits are made: preheat, instant-start, andrapid-start.

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Figure 7.3 Fluorescent lamp shapes and sizes at one-eighth actual size.

The earliest fluorescent lamps were ofthe preheat kind (figure 7.4). Preheat lampshave cathodes that must be heated electri-cally in order to make them emit electronsand thus ionize the gas in the tube, making itmore conductive and raising the voltage nec-essary to strike the arc. The current heats thecathodes; because this occurs before the arcstrikes, it is said to preheat them.

The preheating process takes a few sec-onds. It is usually controlled by an automaticstarter, which applies current to the cath-odes of the lamp for a sufficient length oftime to heat them; it then automaticallyshuts off, causing the voltage to be appliedbetween the cathodes and striking the arc.

The preheating is sometimes accom-plished by holding down a manual start

button, as with some fluorescent deskluminaires. The button is held down for a fewseconds while the cathodes heat; when thebutton is released, the arc strikes. Whetherstarted manually or automatically, once thelamp is in operation, the arc maintains thecathode temperature.

Instant-start lamps are designed tooperate without a starter (figure 7.5). Thissimplifies the lighting system and its mainte-nance. The ballast provides sufficient voltage

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Figure 7.4 Preheat fluorescent lamp diameters andbases at one-half actual size.

Figure 7.5 Instant-start lamp diameters and bases atone-half actual size.

to strike the arc instantly. This is a violentaction that requires cathodes able to with-stand the jolt of instant starting.

Because preheating is unnecessary withinstant-start lamps, only one external con-tact is located on each end of the lamp.Some instant-start lamps have bipin bases;lamps with single-pin bases are calledslimline lamps. In these lamps, the pins areconnected inside the base.

Slimline lamps can be operated at morethan one current and wattage. For thisreason, they are identified by length rather

than lamp wattage. The number followingthe “F” in the designation is the nominallamp length. For example, F96T12/RE830 isa 96 in (8 ft), 1½-in-diameter, slimline lampwith rare-earth phosphors and a correlatedcolor temperature of 3000 K.

Rapid-start lamps combine the featuresof the preheat and instant-start circuits(figure 7.6). Starters are unnecessary. Theballasts have separate windings that heatthe cathodes continuously; the lamps startalmost instantly after being switched on, butless voltage is required for starting than with

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Figure 7.6 Rapid-start lamp diameters and bases at one-half actual size.

instant start lamps of comparable length.Rapid-start ballasts are less expensive,smaller, and have lower power loss thaninstant-start ballasts.

Rapid-start lamps are sometimes oper-ated with instant-start ballasts. The instant-start ballasts provide higher voltage to startthe lamps, but they do not supply current tothe cathodes during lamp operation. Thesavings is approximately 2 to 3 watts perlamp.

Because the cathodes of rapid-startlamps are heated continuously during opera-tion, these are the only fluorescent lampsthat can be dimmed or flashed.

Trigger-start ballasts permit the opera-tion of preheat fluorescent lamps up to 32 Wwithout the use of starters. This circuit wasdeveloped prior to the rapid-start circuit andis similar in operation: it provides continuousheating of the cathodes, and starters areunnecessary. The lamps are made with bipinbases to permit the flow of current throughthe cathode filaments before the lamp starts.

For reliable starting, rapid-start and trig-ger-start lamps must be mounted within 1 inof a 1-in-wide grounded strip of metal, orwithin ½ in of a ½-in-wide grounded strip ofmetal, running the full length of the lamp.This is usually provided by a wiring channelor reflector in the luminaire housing.

T8 and T5 lampsGood color-rendering fluorescent lampsrequire the use of rare-earth phosphors,which are more expensive than standardphosphors. For this reason, smaller-diame-ter T8 and T5 lamps are produced. (The T8[1-in-diameter] bulb uses only two-thirds ofthe phosphor quantity required by the T12[1½-in-diameter] bulb, for example; it istherefore less expensive to produce.) Thesmaller diameter also gets the phosphorscloser to the arc, increasing the efficiency oflight generation.

In addition to better color rendering, therare-earth phosphors provide a substantialincrease in lighting efficiency. Systemefficacies up to 80 lumens per watt for T8lamps on magnetic ballasts and up to 105lumens per watt for T8 lamps on electronicballasts compare with 65 to 75 lumens perwatt with T12 lamps and ordinary phos-phors. Due to their higher efficacies, T8lamp-ballast systems have replaced conven-tional T12 lamps in many applications.

(Lamp manufacturers report lamp effi-cacy: lumens per watt when the lamp isoperated under reference conditions.System efficacy is lumens generated by thelamp when operated by a given ballastdivided by the input watts to the ballast.)

As tube diameter decreases in size,luminance is increased, requiring bettermethods of shielding the source. The smallerbulb diameter also increases the luminaireoptical efficiency, however, yielding smallerluminaires with the potential for improvedlight-distribution patterns.

For T8 lamps, three kinds of rare-earthphosphors are available: RE-70, RE-80, andRE-90. Color temperature is varied accord-ing to the relative balance among the phos-phors. RE-70 and RE-80 lamps have threenarrow-emission phosphors that producethree “peaks” of visible energy: a blue, agreen, and a red (see color plates 19, 20,and 21). RE-70 lamps contain a coat of con-ventional phosphors and a thin coat of therare-earth triphosphors to produce a CRI of70 to 79. RE-80 lamps contain a thick coatof the rare-earth triphosphors, increasingCRI to 80 to 89 with full light output andlumen maintenance.

RE-90 lamps do not use the threenarrow-emission phosphors of the other tworare-earth lamps. These quad-phosphorlamps contain four wider-emission phosphorsthat produce CRIs of 95 at 3000 K and 98 at5000 K (see color plates 22 and 23).

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In addition to the four rare-earth phos-phors, the RE-90 3000 K lamp has filters toreduce the quantity of blue light caused bymercury radiation, balancing the color. Lightoutput of RE-90 lamps is reduced by one-third, but this is often imperceptible becauseof the vivid and accurate colors, whichimprove contrast and portray tones that areotherwise grayed with lamps of lower CRIs.

T5 (5 8-in-diameter) fluorescent lampsare only manufactured in metric lengths andwith a miniature bipin base, and aredesigned to operate solely on electronic bal-lasts. Their smaller diameter provides evenbetter optical control than T8 lamps. Addi-tionally, T5 lamps produce optimum lightoutput at an ambient temperature of 95ºF(35ºC) rather than the more typical 77ºF(25ºC) of other fluorescent lamps, allowingfor the design of more compact luminairesthat do not require added size to dissipateheat.

T5 lamps are also available in high-output versions providing almost twice thelight output per length as their standard T5counterparts. At the present time, all T5lamps are available only with RE-80 phos-phors.

VariationsEnergy-saving or reduced-wattage lamps areinterchangeable with standard lamps; theyconsume less power and deliver less light.Input wattage is reduced by 12 to 15 per-cent; lumen output is reduced by 10 to 20percent. Energy-saving lamps are more sen-sitive to low temperatures than standardlamps: minimum starting temperature is60°F, as opposed to 50°F for standardlamps.

T8 and T12 U-bent fluorescent lampsare regular 4-ft lamps bent into a “U” shape.This configuration allows two or three 4-ftlamps to be used in a 2-ft-square luminaire,with the further advantage of wiring and

lampholders being conveniently located atone end of the luminaire.

T8 U-bent lamps are available in 158-in

and 6-in leg spacing, with the 6-in leg spac-ing more common. T12 U-bent lamps areavailable in 35

8-in and 6-in leg spacing, withthe 6-in leg spacing again more common.

Circular “circline” lamps are T9 (118-in-

diameter) tubes bent in a circle with the twoends adjacent to each other and a single,four-pin connector base. They are availablein 6½-, 8¼-, 12-, and 16-in outside diame-ters. Circline lamps are of the rapid-startdesign but operate equally well on preheat ortrigger-start ballasts.

Circular T5 lamps are also available, in9- and 12-in outside diameters. These lampshave a single base with a two-pin connector.

High-output (HO) T12 rapid-start lampsoperate at 800 milliamperes (mA), com-pared with 425 mA for most standard rapid-start lamps. They produce about 45 percentmore light than slimline lamps of corre-sponding physical size as a result of drawingconsiderably more current than the standardlamps.

High-output lamps are identified bylamp length, bulb diameter, color, and theletters HO. For example, F96T12/RE830/HOis an 8-ft, 1½-in-diameter, rare-earth, 3000K, high-output lamp. HO lamps are availablein lengths from 18 to 96 in, with a variety ofphosphors and color temperatures, and inreduced-wattage, energy-saving versions.

Very-high output (VHO) T12 lamps alsooperate on the rapid-start principle at 1500mA. They produce up to twice as much lightas standard lamps of equal length, whileusing approximately three times more power.These are the most powerful fluorescentlamps available.

Reflector and aperture lamps contain aninternal reflector on part of the inner surfaceof the tube to provide built-in directional lightcontrol. The un-reflectorized portion of the

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D I S C H A R G E L A M P S

tube is called the window. Intensity of lightemitted through the window is significantlyincreased; total light output is reduced, how-ever. Except in special applications, regularlamps in efficient luminaires perform better(figure 7.7).

Compact fluorescent lampsCompact fluorescent lamps provide high effi-cacy, a CRI of 82, and 10,000- to 20,000-hr lives in a single-ended, multi-tube fluores-cent lamp (figure 7.8). They operate in thepreheat and rapid-start circuit modes; manyhave a starter built into the lamp base.

Compact fluorescent lamps have signifi-cantly higher lumen output per unit lengththan conventional small fluorescent lamps.This is the result of high phosphor loading,which is necessary because of their smalldiameter and sharp-cornered, multi-tubebulb shape. As with all fluorescent lamps,compact ones require a ballast in order tostart and operate properly.

The compact lamps use the same high-color-rendering rare-earth phosphors as theT5 and T8 lamps mentioned earlier. Colortemperature varies according to the relativebalance among the phosphors. The 2700 K

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Figure 7.7 Reflector and aperture fluorescent lamps at one-half actual size.

color temperature is often used to simulatethe color of standard incandescent lamps;3000 K is compatible with tungsten-halogenand linear, straight-tube 3000 K fluorescentlamps; 3500 K and 4100 K are compatiblewith straight-tube 3500 K and 4100 K fluo-rescent lamps, respectively.

There are six families of compact fluo-rescent lamps:

1. T4 (½-in-diameter) twin-tube preheatlamps have starter devices in the two-pinplug base of the lamp. These lamps oper-ate on inexpensive reactor ballasts andare available from 5 W to 13 W (figure7.8).

2. T4 or T5 (5 8-in-diameter) quad-tube pre-heat lamps have two-pin plug bases andintegral starters; they are available from13 W to 26 W (figure 7.9). Some of these

lamps use reactor ballasts; others requireautotransformer/reactor ballasts. Designedto be a more compact, higher lumenoutput variation of the twin-tube kind, theyprovide a substantial increase in lightoutput compared to twin-tube lamps.

3. T4 quad-tube electronic lamps are similarto the quad-tube preheat lamps, exceptthat they have four-pin plug bases and nointegral starters; they are available from13 W to 26 W (figure 7.9). Designed foroperation with electronic rapid-start bal-lasts, they also operate on preheat cir-cuits. These lamps can be dimmed with anelectronic dimming ballast.

4. T4 triple-tube rapid-start/preheat lampshave four-pin plug bases without starters;they are available from 18 W to 70 W(figure 7.10). Designed to deliver high

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Figure 7.8 Twin-tube compact fluo-rescent lamp at one-half actualsize.

Figure 7.9 Quad-tube compactfluorescent lamp at one-half actualsize.

Figure 7.10 Triple-tube compactfluorescent lamp at one-half actualsize.

lumen output from a small package, theyare frequently used in recessed luminairesthat resemble familiar incandescent down-lights and wall-washers. These lamps canbe dimmed with an electronic dimming bal-last.

5. T5 twin-tube “long” rapid-start/preheatlamps have a four-pin in-line base with-out a starter; they are available from 18W to 80 W (figure 7.11). These arehigher-output lamps, designed to providethe lumen output of conventional fluores-cent lamps in smaller packages. Theselamps can be dimmed with an electronicdimming ballast.

6. Self-ballasted compact fluorescent lampsare designed to directly replace incan-descent lamps, providing savings inenergy and maintenance. They are acomplete system, containing a double-folded compact fluorescent lamp, aninstant-start electronic ballast, an outerdiffuser, and a medium screw base(figure 7.12). They are available in twokinds: modular (replaceable lamp) andnon-modular. The lamps consume one-fourth to one-third as much energy astheir incandescent counterparts and lastup to ten times longer. These compactfluorescents with medium screw basesare less efficacious than other compact

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Figure 7.11 “Long” compact fluorescent lamp at one-quarter actual size.

Figure 7.12 Non-modular, self-ballasted, compactfluorescent lamp.

fluorescent lamps, but offer a means ofeasily increasing the efficiency of anincandescent luminaire.

Light outputDuring the first one hundred hours of burninga new fluorescent lamp, the initial lumenoutput drops by about 5 percent; lumenreduction thereafter is less rapid. Conse-quently, the published “initial lumens” forfluorescent lamps is the value obtained afterthe first hundred hours of burning.

The depreciation in light output duringthe life of the lamp is approximately 15 per-cent of the initial lumens. This is the result ofthe gradual deterioration of the phosphorpowders and the evaporation of electron-emissive material from the cathodes, whichcauses blackening of the glass bulb adjacentto the cathodes.

The end of life is reached when theemission material on either cathode isdepleted. Failed preheat lamps flash on andoff or extinguish; instant-start and rapid-startlamps extinguish, flicker, or operate atreduced luminance.

Lamp lifeLamp life varies with the different kinds offluorescent lamps. Rated average life of fluo-rescent lamps is based on the average life ofa large representative group of lamps testedin a laboratory under controlled conditions; itis expressed in “burning hours.” Preheatlamps have rated average lives of 7,500 to9,000 hrs, slimline lamps 7,500 to 12,000hrs, rapid-start lamps 14,000 to 24,000hrs, high-output lamps 9,000 to 12,000hrs, and very-high-output lamps 10,000 to12,000 hrs.

The starting of all fluorescent lamps isaffected by the ambient temperature. Lowtemperatures require higher voltages for reli-able starting. The majority of ballasts providevoltages that start standard lamps down to

50°F. Ballasts are available for certain kindsof lamps that can start lamps down to 0°Fand down to –20°F.

Because each start further depletes thetungsten cathodes, the average life of fluo-rescent lamps is affected by the number oflamp starts. Frequent starting shortens life;life is lengthened as the number of burninghours per start is increased. Published lamp-life ratings are based on an arbitrarilyassigned three hours of burning per start.The life of cold-cathode lamps is unaffectedby the number of starts.

EPACTThe U.S. Energy Policy Act of 1992 (EPACT)established minimum efficacy standards forcertain kinds of fluorescent lamps. The effi-cacy standards are a combination of mini-mum average lamp efficacy, measured inlumens per watt, and minimum color render-ing index (CRI). No full-wattage F40, F40/U,F96, or F96/HO lamps can be manufacturedor imported unless the lamp has a CRI of 69or higher and meets the minimum-efficacyrequirement.

Full-wattage CW, D, W, WW, and WWXlamps are now unavailable; energy-saving Dand WWX lamps are unavailable. CW, D, LW,W, WW, and WWX F96T12 and F96T12/HOlamps have been prohibited from manufac-ture or sale in the United States since 30April 1994. CW, D, LW, W, WW, and WWXF40T12 and F40T12/U lamps have beenprohibited from manufacture or sale in theUnited States since 31 October 1995. Seetable 3 in the Appendix.

Lamps with a CRI of 82 or higher areexempt from these efficacy standards. Inaddition, aperture, cold-temperature, col-ored, impact-resistant, plant growth, reflec-tor, and ultraviolet lamps are exempt fromthe standards.

Until 1992, most fluorescent lampsused for architectural lighting in the United

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States were T12 bulbs with less expensivephosphors and poorer color rendering. Thecombination of high efficacy and good colorrendering has made the T8 lamp the currentstandard.

Colored LampsColored fluorescent lamps emit only a partic-ular portion of the spectrum; the color isdetermined by the selection of the phos-phors used. Different mixtures of phosphorcomposition produce different colors of light.

In a few cases, additional filtering isrequired to absorb mercury radiations thatwill otherwise desaturate the color. For redand deep blue lamps, a filter coating isapplied to the outside bulb wall.

The gold fluorescent lamp achieves itscolor by subtraction, because no phosphorsemit mainly yellow light. A yellow filter coat-ing on the inside of the tube absorbs theunwanted wavelengths from a warm-whitephosphor. Whenever subtractive filtering isused, luminous efficacy is reduced.

Black light fluorescent lamps use a spe-cial phosphor that emits primarily near-ultra-violet energy, plus a small amount of visibleblue light.

Colored fluorescent lamps vary widely inlumen output. For example, twenty-five redlamps are required to equal the lumenoutput of one green lamp. See table 6 in theAppendix.

Different colors of light have differentdegrees of effectiveness in attracting atten-tion; this is independent of brightness inten-sity. See table 8 in the Appendix.

Flicker and Stroboscopic EffectThe mercury arc in a fluorescent lamp oper-ated on a 60 Hz alternating current goes onand off 120 times per second. The light fromthe lamp remains visible because the phos-phors have some phosphorescent or “carry-over” action: they emit a reduced quantity of

light for a short period of time after the arc isextinguished.

The cyclic variation in light output isknown as flicker. With 60 Hz operation, theflicker rate over the length of the lamp is 120cycles per second. At the ends of the lampeach alternate flash is relatively weak,occurring at a rate of 60 flashes per second.

The 120-cycle flicker is too fast to bevisible. The 60-cycle flicker can be detected,but only by the peripheral vision of the retina.For this reason, lamp flicker is seldomnoticed except when seeing the ends oflamps out of the corner of the eye.

When rapidly moving objects areobserved under discharge lighting systems,blurred “ghost” images are sometimesobserved. This is known as stroboscopiceffect. Because of this phenomenon, anobject moving at a uniform speed will appearto move in jerks. Under extreme conditions, arotating object will seem to be standing still oreven rotating in reverse direction dependingon its speed of rotation and its configuration.

Stroboscopic effect rarely causes diffi-culty because modern phosphors have rela-tively long carryover periods. If a problemoccurs, operating multiple ballasts on allthree phases of a three-phase circuit willreduce stroboscopic effect because onlyone-third of the lamps operate at reducedoutput at a given time.

HIGH-INTENSITY DISCHARGE (HID)LAMPSThe term “high-intensity discharge” appliesto arc-discharge sources with a high powerdensity. In HID lamps, light is produced bypassing an electric current through a gas orvapor under high pressure, as contrasted tothe low pressure in fluorescent or low-pres-sure sodium lamps. HID lamps used for illu-mination belong to three principal families:

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(1) mercury vapor, (2) metal halide, and (3)high-pressure sodium lamps.

HID lamps consist of an arc tube enclos-ing two electrodes and one or more metalsthat are vaporized and ionized to conductcurrent in an electric arc from one electrodeto the other. When a lamp is energized, anelectric field is established between thestarting electrode and the main electrode,causing individual particles of the startinggas to become electrically charged (figure7.13). With most HID lamps, the arc tube isenclosed in an outer glass bulb.

The electrons that comprise the currentstream, or arc discharge, are accelerated totremendous speeds. When they collide withthe atoms of the gas or vapor, they tempo-rarily alter the atomic structure, and lightresults from the energy given off in the formof radiation as the atoms return to theirnormal state. The lamp warm-up processtakes three to seven minutes, depending onambient temperature conditions.

Each kind of HID lamp is unique. Withmercury vapor lamps, light is produced by anelectric discharge through mercury vapor.The electrodes are made of tungsten, inwhich an emission material is embeddedwithin the turns of an inner tungsten coil pro-tected by an outer tungsten coil. The elec-trodes are heated to the proper electron-emissive temperature by bombardmentenergy received from the arc. After the arcstrikes, its heat begins to vaporize the mer-cury, which results in poor color quality of agreenish hue: 15 to 20 CRI (color plate 27).The addition of phosphor coatings on theinside of the bulb improves color rendering:45 to 50 CRI (color plate 28).

In metal halide lamps, the electric dis-charge is through the combined vapors ofmercury and metal halides, which are intro-duced into the arc tube as compoundiodides. When the lamp attains its full oper-ating temperature, the metal halides in thearc tube are partially vaporized and themetals radiate their spectrum. The metalhalides radiate a wider spectrum than themercury lamp, yielding greater efficacies andbetter color rendering: 65 CRI (color plate29). The addition of phosphor coatings onthe inside of the bulb provides diffusion andsome additional color improvement: 70 CRI(color plate 30).

Pulse-start metal halide lamps use anarc tube with substantially higher fill pres-sure than standard metal halide lamps. Thisreduces tungsten evaporation from the elec-

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Figure 7.13 Typical high-intensity discharge lamp. Withall HID lamps, the light-producing element is the arctube; it contains metallic vapors, gases, and the elec-trodes at the ends of the arc tube, where the arc origi-nates and terminates. The base connects the lampmechanically and electrically to the luminaire.

trodes, which lessens the darkening of thearc tube. As a result, pulse-start lamps pro-vide better lumen maintenance, longer lamplife, and improved color stability comparedwith standard metal halide lamps.

With high-pressure sodium (HPS)lamps, the electric discharge is throughcombined vapors of mercury and sodium,with the latter dominating. This produces theorange-tinted color familiar to us in streetlighting: 21 to 22 CRI (color plate 24). InHPS lamps, the inner arc tube is constructedof polycrystalline alumina (PCA), a ceramicmaterial that is resistant to sodium attack athigh temperatures and has a high meltingpoint. By further increasing the gas pressureinside the lamp, white high-pressure sodiumlamps produce incandescent-like color at2700 K with good color-rendering propertiesand a CRI of 85 (color plate 25).

Ceramic metal halide lamps combinethe ceramic arc tube technology of high-pressure sodium lamps with existing metalhalide chemistry. Instead of the quartz arctube used in conventional metal halidelamps, ceramic metal halide lamps have anarc tube made of polycrystalline alumina(PCA). PCA permits the lamp to operate athigher internal temperatures, increasingcolor rendering, output, and efficacy. PCAresists interaction with the chemicals insidethe tube, which stabilizes the chemical mixover the life of the lamp, improving colorconsistency and lumen maintenance. ThePCA tube is smaller than quartz tubes,which prevents the chemical mix from dis-persing and further improves color consis-tency.

Many high-color-rendering HID lampshave shorter lives and produce lower lightoutput than standard HID lamps, but theirsuperior color makes them the best choice forareas inhabited by people. White high-pres-sure sodium lamps offer 10,000-hr lives and a

CRI of 85, and some have prefocus bases toprovide precise location of the source in opti-cal systems. Ceramic metal halide lamps offer6,000- to 15,000-hr lives and CRIs of 81 to96; some have bipin, recessed single-contact,or mogul bipost bases to ensure accuratealignment of the light source with the opticalsystem of the luminaire.

Bulb shapesHID bulbs are produced in several incandes-cent bulb shapes. In addition, four shapeshave been specially designed for HID ser-vice: B, BT, E, and ED. Bulb shapes (figure7.14) include

A Arbitrary

B Bulged

BT Bulged-tubular

E Elliptical

ED Elliptical-dimpled

PAR Parabolic aluminized reflector

R Reflector

T Tubular

The descriptive abbreviation of an HIDlamp includes a multi-letter code that identi-fies the lamp kind or trade name and anumber that identifies the lamp’s wattage,followed by suffixes that may include lampshape, a number that represents the maxi-mum diameter of the bulb in eighths of aninch, outer bulb finish, operating position,base, and color. The American National Stan-dards Institute (ANSI) code for description ofHID lamps provides suggested standardizednomenclature among manufacturers.

Example: CMH100/C/U/MED/830

CMH ceramic metal halide lamp, alsoCDM (for ceramic discharge metalhalide) and MHC for metal halideceramic)

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95Figure 7.14 HID lamp shapes at one-half actual size.

H mercury vapor lamp (H stands forfor hydrargyrum, the Greek wordfor mercury and the source of itschemical symbol Hg)

M metal halide lamp

S or LU high-pressure sodium lamp (LU isshort for the trademarked name ofseveral manufacturers’ HPS lamps)

SB self-ballasted mercury lamp (forincandescent retrofit)

T self-extinguishing mercury or metalhalide lamps (these stop operatingif the outer bulb is broken to protectpeople from exposure to excessiveUV radiation; the designation isomitted with non-self-extinguishinglamps.1

39 with mercury lamps, two-digit num-bers denote electrical propertiesand kind of ballast required;lamps with the same numbers areelectrically interchangeable (doublenumbers such as 43/44 indicatethat the lamp will operate frommore than one ballast).

100 with metal halide and HPS lamps,the number specifying nominallamp wattage.

/C phosphor-coated (metal halide)

/D diffuse-coated (HPS)

/U manufacturer-designated symbolsappear after the next slant line;these commonly identify color orburning position (e.g., U = univer-sal burning position).

/BD base down to horizontal ± 15°

/BU base up to horizontal ± 15°

/DX deluxe white phosphor

/HOR base horizontal ± 15°

/MED medium screw base

/T tubular bulb

/U universal burning position

For optical control, clear lamps offer a rel-atively small “point source” of 21

8 in to 9½ inin length. The phosphor-coated lamps enlargethe optical size of the source to the outer bulbwall; although the phosphor coating enhancesthe lamps’ color-rendering abilities, theincreased optical size dictates the use of largereflectors for useful optical control.

Lamp OperationAs with fluorescent lamps, HID lamps requireballasts to regulate the arc current flow andto deliver the proper voltage to strike the arc.Electronic ballasts are more efficient andprovide more precise control of the arc tubevoltage over the lamp’s life, resulting in moreconsistent color and longer life.

Extinction of a lamp occurs in one ofthree ways: (1) a power interruption of morethan half a cycle, (2) a severe voltage dip ofmore than a few cycles, or (3) insufficientvoltage maintained from the ballast.

Before the lamp will relight, it must coolsufficiently to reduce the vapor pressure to apoint where the arc will restrike. The timerequired to cool depends partly on aluminaire’s ability to dissipate heat. Typicallyin a luminaire, mercury vapor lamps willrelight in three to ten minutes. Metal halidelamps require ten to twenty minutes torestrike; pulse-start metal halide lampsrelight in four to eight minutes. High-pres-sure sodium lamps usually restrike inapproximately one minute. “Instant-strike”HPS lamps have a second arc tube that pro-duces light instantly after a momentarypower interruption.

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1Mercury and metal halide lamps will cause serious skinburn and eye inflammation from shortwave ultravioletradiation after only a few minutes when the outer enve-lope of the lamp is broken or punctured if adequateshielding is not used.

Light OutputDepreciation in light output during life occursmainly because of the escape of electron-emissive material and tungsten from thecathodes to the walls of the arc tube. Thisdepends in part on the frequency of starting;therefore, long burning cycles increase lamplife and lumen maintenance. Other factorsaffecting lumen maintenance are operatingcurrent and the current wave form producedby the ballast design.

The light output of metal halide lampsdeclines more rapidly than either mercuryvapor or HPS lamps. With ceramic metalhalide lamps, lumen maintenance isimproved approximately 30 percent. Fre-quent starting is most harmful to metalhalide, less harmful to HPS, and least harm-ful to mercury vapor lamps.

Lamp LifeLamp life varies considerably depending onthe kind of HID lamp and its burning orienta-tion. The rated average life of HID lamps isthe point at which approximately 50 percentof the lamps in a large group have burnedout and 50 percent remain burning. Pub-lished lamp-life ratings are based on tenhours per start.

The normal mode of failure of a mercuryvapor lamp is its inability to light. Almost allmercury vapor lamps have rated averagelives of 24,000+ hrs (the plus sign indicatesthat in 50 percent of such lamps “burnout”occurs in excess of 24,000 hrs). It is wise torelamp before reaching the point of failure,however, because the lamps continue tooperate long after they are a useful lightsource.

Metal halide lamps have rated averagelives of 7,500 to 20,000 hrs, depending onlamp wattage. Lives of metal halide lampsare shorter than those of other HID lampsbecause of inferior lumen maintenance and

the presence of iodides in the arc tubes. Thenormal mode of failure is the inability to lightbecause of an increased starting voltagerequirement. Metal halide lamps are particu-larly sensitive to frequency of starting. Aswith all lamps, over-wattage operation alsoshortens life.

Almost all HPS lamps have rated aver-age lives of 24,000 hrs. Normal end of lifeoccurs when the lamp begins to cycle on andoff, the result of lamp voltage havingincreased to the point where the ballast volt-age is insufficient to keep the lamp lighted.Over-wattage operation causes voltage torise faster; slight under-wattage does notaffect lamp life.

As with fluorescent lamps, the initiallumen rating for HID lamps is measured afterthe first one hundred hours of operation.This “seasoning” is necessary because thelamps depreciate rapidly during these firsthundred hours, when cleanup of impuritiestakes place.

DimmingIt is possible to dim some HID lamps usingspecial ballasts, but operating HID lamps atless than full output will produce color shiftsand reduced lamp efficacy. As wattagedecreases, the color-rendering properties ofmetal halide lamps approach the color ofmercury vapor; HPS lamps approach theyellow-amber color of low-pressure sodium.mercury vapor lamps will retain their alreadyinferior color properties reasonably well, butlumen maintenance and length of life arereduced.

LOW-PRESSURE SODIUM (LPS) LAMPSLow-pressure sodium (LPS) lamps, althoughtechnically not high-intensity dischargesources, are used in limited applications.They have high efficacies—up to 200

97


lumens per watt—but their extremely narrowspectral range makes these lamps unsuit-able for use in interiors (color plate 26).

The lamp, consisting of two tubes, oneinside the other, has a mixture of neon andargon gas, plus sodium metal in the innertube and an evacuated outer bulb. Initially,the arc discharge is through the neon andargon gas and, as the sodium metal heatsup and vaporizes, the yellow-amber color ofsodium is produced (figure 7.15).

The light produced by the LPS arc, con-sisting only of radiation in the yellow regionof the visible spectrum, is monochromatic.No mercury is present in the discharge; UVradiation emission is not a concern if theouter bulb breaks. The LPS lamps requirespecific ballasts; no retrofit lamps exist.

In contrast to HID sources, LPS systemsmaintain constant lumen output over lifeand light output is unaffected by changes inambient temperature. Normal end of lifeoccurs when the lamp fails to start or warmup to full light output.

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Figure 7.15 Low-pressure sodium lamp construction.

8Auxiliary EquipmentAll discharge sources and low-voltage incandescent sources require the use of

auxiliary equipment to supply the correct current or voltage or both to the source.

Auxiliary equipment falls into two categories:transformers and ballasts. This auxiliaryequipment consumes a small amount ofelectrical power, adding to the total amountof wattage used by the lighting system.

TRANSFORMERSLow-voltage light sources require the use ofa transformer to step down the standardbuilding service of 120 V to 12 V. The nomi-nal 120 V building service can vary between115 V and 125 V; some low-voltage lightsources operate at 6 V or 24 V. Transformersare placed either within (integral to) theluminaire or in a remote location.

The smaller size of many low-voltagelight sources allows for the design of smallerluminaires. With recessed luminaires thetransformer is hidden above the ceiling andout of view. With surface- or pendant-mounted luminaires that have their trans-formers enclosed within the housing, how-ever, the bulk of the luminaire is increased.Where ceiling conditions permit, surface-and pendant-mounted luminaires can bedesigned with the transformer recessed inthe ceiling and out of view.

Track-mounted luminaires usually con-tain their transformers. It is also possible toprovide low-voltage service to a length oftrack, locating the transformer in the ceilingor in an ancillary space. The high amperageof low-voltage lamps strictly limits thenumber of track luminaires per transformer(W ÷ V = A): a 50 W, 12 V lamp draws thesame amperage as a 500 W, 120 V lamp;therefore, a 20-ampere-rated track can ser-vice only four 50 W lamps (50 W × 4 ÷ 12 V= 16.7 A). This problem is reduced by theuse of 50-amp track, which permits ten 50W, 12 V lamps to be installed on a singletrack circuit (50 W × 10 ÷ 12 V = 41.7 A).

If remote transformers are used tomaintain the compactness of the lightingelement, the increased distance betweenthe source and its transformer requireslarger wire sizes to prevent a voltage dropfrom occurring over the longer wiring run.See table 9 in the Appendix.

Two kinds of transformers are manufac-tured for low-voltage lighting: magnetic(core-and-coil) and electronic (solid-state).

Magnetic transformers use copperwound around a steel core, which is induc-

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tive by nature. Magnetic transformers arerelatively large and heavy. Properly sized forthe lamp load, they have a long life expec-tancy. They sometimes cause a noise prob-lem by producing an audible 60-cycle“hum.” Toroidal (doughnut-shaped) mag-netic transformers are quieter, but they alsohum when controlled by some kinds of elec-tronic dimmers. The hum grows with thenumber of luminaires in a room, and theluminaires, if improperly designed, will reso-nate with their transformers.

Electronic transformers use electroniccircuitry, which is capacitive by nature. Elec-tronic transformers are compact, light-weight, and quiet. But their life is shorterthan magnetic units, premature failures arecommon, and they are incompatible withsome dimmers. The small dimensions ofelectronic transformers outweigh many ofthese flaws, however. The designer mustconsult the dimmer manufacturer to ensurethe compatibility of transformers and dim-mers.

BALLASTSAll lamps, except incandescent ones, requirea ballast. Every discharge source has nega-tive resistance characteristics. If the arcdischarge is placed directly across a non-regulated voltage supply, it will draw an

unlimited amount of current almost instantlyand will be quickly destroyed. Therefore, acurrent-limiting device called a ballast isinserted between the discharge lamp andthe power supply to limit the electric currentflow through the arc discharge (figure 8.1).

Besides limiting the current flow, theballast also provides the correct voltage tostart the arc discharge. It transforms theavailable line voltage to that required by thelamp.

Traditionally, ballasts have not beeninterchangeable. Most ballasts are designedto provide the proper operating characteris-tics for only one kind of lamp. For example,175 W M57 metal halide lamps are inopera-ble on ballasts intended for 175 W H39 mer-cury vapor lamps, and vice versa.

Newer electronic ballasts are designedto operate more than one connected load.For example, several manufacturers offerballasts that can operate either one, two, orthree fluorescent lamps.

Lamp wattage is controlled by the bal-last, not by the lamp. If a 100 W HPS lamp isoperated on a 400 W ballast, it will operateat 400 W, to the detriment of the lamp’s per-formance. This may also lead to prematureballast failure.

Unlike incandescent lamps, the ratedwattage of a discharge lamp is the wattage

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Figure 8.1 Typical F32T8 120 V ballast.

at which it is designed to operate, not thewattage at which it will operate. Therefore, itis impossible to reduce the wattage of a dis-charge system simply by changing the watt-age of the lamps. The ballasts must also bechanged.

Two-lamp fluorescent ballasts are usedfrequently to reduce ballast cost and instal-lation cost per unit of light. They are avail-able for two-lamp series operation or two-lamp parallel operation.

Two-lamp series designs are more com-mon because they offer the lowest cost andthe minimum size and weight. Only two lampleads are supplied from the ballast. Bothlamps go out when one lamp fails; the goodlamp remains undamaged.

Two-lamp parallel designs have twoindependent ballast circuits and thereforeare more expensive than two-lamp seriesdesigns. Three or six lamp leads are suppliedfrom the ballast. Failure of one lamp leavesperformance of the second lamp unaffected.

Electromagnetic BallastsUntil the 1980s, all discharge ballasts wereof the electromagnetic kind. The electro-magnetic ballast consists of two copper oraluminum wire coils around a common coreof steel laminations. This assembly convertselectrical power into a form appropriate tostart and regulate the lamp.

The ballast usually consists of a trans-former, inductance coils, and a capacitor.The transformer converts the service voltageof the lighting circuit to the starting voltagerequired for the lamp. The inductance coillimits the current that can be drawn by thelamp, but in so doing introduces inductivereactance into the circuit. The capacitorrealigns the phase relationship between volt-age and current; it is a controlling device thatconsumes no electrical power.

The capacitor improves the ballast’spower factor so that it uses energy more effi-ciently. An electromagnetic ballast that isequipped with a capacitor is called a high-power-factor ballast.

Power FactorThe power factor of a ballast is the measure-ment of how effectively the ballast convertsthe voltage and current supplied by the elec-trical distribution system to the power deliv-ered by the ballast to the lamp. Perfectphase relationship would result in a powerfactor of 100 percent.

Power factorInput watts (W)

Line volts (V) Line=

× amps (A)

The power factor of an inductive circuitis lagging (figure 8.2) and that of a capaci-tive circuit is leading. When discharge lampsare operated in conjunction with simple

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A U X I L I A R Y E Q U I P M E N T

Figure 8.2 Power factor.

inductive ballasts, the overall power factor is50 to 60 percent. With a capacitor, the lead-ing current drawn by the capacitor compen-sates for the lagging current in theremainder of the circuit, improving the powerfactor.

Ballasts are classified according to oneof the following three categories:

High power factor: 90% or greater

Power factor corrected: 80 to 89%

Low (normal) power factor: 79% or less

High-power-factor ballasts use thelowest level of current for the specific amountof power needed; this reduces wiring costs bypermitting more luminaires on branch cir-cuits. Low-power-factor ballasts use higherlevels of current—approximately twice theline current needed by high-power-factor bal-lasts—allowing fewer luminaires per branchcircuit and increasing wiring costs.

Power factor is not an indication of thelamp-ballast system’s ability to producelight; power factor measurements pertainonly to the ballast’s ability to use the powerthat is supplied. Thus, power factors areinvalid as a multiplier in determining lightoutput values.

Lamp-Ballast System EfficacyThe initial lumen and mean-lumen ratingspublished by lamp manufacturers are basedon the operation of the rated lamps by a ref-erence ballast. This is a laboratory instru-ment that is used to establish a baseline, orreference conditions, so that commerciallyavailable ballasts can be compared againstthe same reference. Some commerciallyavailable ballasts operate lamps more effi-ciently than the reference; others operatelamps less efficiently.

In practice, when a lamp is operated bya commercially available ballast, it usuallyprovides fewer lumens than the rated

amount. Because of the electrical resistancecreated by the passage of a current throughthe core-and-coil of an electromagnetic bal-last, some power is converted to heat. Thislost power, called ballast loss, is unusablefor producing light from the lamp.

The disparity between light provided bythe reference ballast and the commerciallyavailable ballast is called the ballast factor.The ballast factor is the ratio of light outputproduced by lamps operated by a commer-cially available ballast to that which is theo-retically supplied by lamps powered by alaboratory-reference ballast.

Ballastfactor

Lamp lumen output when operatedwith

=commercial ballast

Lamp lumen output when operatedwith laboratory-reference ballast

The term “ballast factor” implies thatthis is a property of the ballast; it is actually aproperty of the lamp-ballast system. Someballasts have different factors for differentlamps. That is, they have one ballast factorfor operating standard lamps and another foroperating energy-saving lamps.

Ballast factors can be greater than 1.0.A commercial ballast can operate a lamp ina way that produces more lumens than whenthe lamp is operated under reference condi-tions.

The ballast efficacy factor is a ratio ofthe ballast factor to the input watts of theballast. This measurement is used to com-pare the efficiency of various lamp-ballastsystems. Ballast efficacy factors are mean-ingful only for comparing different ballastswhen operating the same quantity and kindof lamp.

Ballast efficacy factor =Ballast factor

Ballast input watts

For a given lighting system, the ballastfactor is an indication of the amount of light

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produced by the lamp-ballast combination;the input watts are an indication of thepower consumed.

For example, a ballast with a ballastfactor of 0.88 using 60 W of input power hasa ballast efficacy factor of 1.47 (0.88 × 100÷ 60 = 1.47). Another ballast using thesame input power with a ballast factor of0.82 has a ballast efficacy of 1.37 (0.82 ×100 ÷ 60 = 1.37). The first ballast thereforeoffers greater efficacy because it has a higherballast efficacy factor (1.47 versus 1.37).

An electromagnetic ballast operatingfrom an alternating current source producesa sound called “hum.” The degree of humvaries depending on the kind of ballast. Toaid in the selection of ballasts, manufactur-ers give their ballasts a sound rating thatranges from A (the quietest, at 20 to 24decibels) to F (the loudest, at 49 decibelsand above).

Electronic BallastsThe electronic ballast, based on an entirelydifferent technology from the electromag-netic ballast, starts and regulates lamps withelectronic components rather than the tradi-tional core-and-coil assembly. The lightingsystems they operate convert power to lightmore efficiently than systems run by electro-magnetic ballasts.

Rather than produce more light output,electronic ballasts are usually designed toproduce the same quantity of light as elec-tromagnetic ballasts, but they use lesspower and thereby reduce energy costs.

HID electronic ballasts provide betteroutput regulation (current and power), inde-pendent of input voltage variations or lampwattage variations. This keeps color output(CCT and CRI) consistent and lumen outputmore uniform. Compared to electromagneticsystems, HID electronic ballasts provideimproved performance in starting, normal,and restrike operations.

The humming sound associated withelectromagnetic ballasts results from thevibration of the steel laminations in the coreand coil. Because electronic ballasts do nothave the laminated core and coil, they are75 percent quieter than comparable A-ratedelectromagnetic ballasts.

Electronic ballasts operate fluorescentlamps at higher frequencies than electro-magnetic ones, with the advantages thatflicker is eliminated and lamp efficacy isincreased. Both of these advantages occurbecause the lamp phosphors are undermore constant excitation with high-fre-quency operation.

Electronic ballasts are also smaller andlighter in weight than electromagnetic ones,typically weighing less than half as muchbecause the electronic components arelighter than the metal components of thecore-and-coil assembly. Because electronicballasts consume fewer watts than electro-magnetic ballasts, they also produce lessheat. This cooler operation yields significantsavings in air-conditioning costs.

Air-ConditioningThe air-conditioning load caused by electriclighting derives from the total lightingsystem, including lamps and ballasts. Eachkilowatt (kW) of electric power used by thelighting system adds 3,412 British thermalunits (BTUs) to the air-conditioning load.

One ton of air-conditioning = 12,000BTU. Therefore, every 3.5 kW of lightingrequires one-ton of air conditioning.

12,0003,452

3.5 kW=

Fluorescent Dimming BallastsElectronic fluorescent dimming ballasts willdim T5, T5 high-output, T8, and T12 fluores-cent lamps to 1 percent of measured lightoutput (10 percent of perceived light). (Light

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A U X I L I A R Y E Q U I P M E N T

output as it is measured is different fromlight perceived by the eye. See page 143.)For four-pin compact fluorescent lamps (T4quad-tube, T4 triple-tube, and T5 long twin-tube), electronic dimming ballasts will dim to5 percent of measured light output (22 per-cent of perceived light). New lamps mustfirst be operated (“seasoned”) for onehundred hours at full power prior to dimmingto achieve proper dimming performance andensure average rated lamp life.

Fluorescent Heater-Cutout BallastsHeater-cutout electromagnetic ballasts havean electric circuit that removes the voltagesupplied to the electrode heaters in rapid-start fluorescent lamps after the lamps areignited and operating. Heater-cutout ballastsconsume approximately 20 percent less inputpower than do standard electromagneticenergy-efficient ballasts; lumen output isreduced by approximately 12 percent.

Other BallastsIn addition to standard ballasts, severalkinds of energy-saving ballasts are made.These fall into two categories: (1) ballaststhat save energy by reducing wattage con-

sumed as well as reducing light output, and(2) ballasts that, because of refinements indesign, save energy chiefly by reducing watt-age loss in the ballasts themselves.

Class P ballasts are equipped with auto-matically resetting thermal protectors. Theseturn off the power when the operating tem-perature exceeds the limits specified byUnderwriters Laboratories (UL) to preventoverheating. When the ballast cools, theprotector resets, restoring operating powerto the ballast.

The UL symbol applied to luminairesindicates that Underwriters Laboratories hasexamined a sample unit and determinedthat it complies with appropriate safety stan-dards. It indicates that when properlyinstalled, such a luminaire will operatesafely. The UL label is also applied to compo-nents, such as transformers and ballasts, tosignify that the components meet safetyrequirements. (The UL label indicates overallluminaire safety when applied to theluminaire and component safety whenapplied to the components. Different labelsand markings are used for various applica-tions, but all make use of the trademark ULcircle.)

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COMPARATIVE FLUORESCENT LAMP-BALLAST SYSTEMS

Ballast kindTypical input power

(W)Typical ballast

factorSystem efficiency

(Lumens/W)

Two F32T8/RS lamps, 32 W each

electromagnetic energy-efficient

electromagnetic heater-cutout

electronic ballast rapid-start

electronic ballast instant-start

70

61

62

63

0.94

0.86

0.88

0.95

78

82

82

87

Two F40T12/RS/ES lamps, 34 W each

electromagnetic energy-efficient

electromagnetic heater-cutout

electronic ballast rapid-start

72

58

60

0.87

0.81

0.85

68

78

79

Light ControlDirectional sources, commonly called reflector lamps, such as AR, MR, PAR,

and R lamps, have built-in optical systems. All other electric light sources

require external devices to modify their distributions in order to be useful in

architectural applications.

These modifications have two purposes: (1)to direct light to where it is wanted and (2) toblock light from where it is unwanted—toshield the lamp from viewing angles thatwould otherwise cause glare. The control oflight direction is accomplished by three meth-ods: reflection, transmission, and refraction.

REFLECTIONReflection is the return of light from a sur-face; it occurs when a portion of the light fall-ing on the surface is thrown back by thatsurface just as a ball bounces back from thefloor. Three kinds of reflection are involved inthe control of light: specular, semi-specular,and diffuse.

Specular reflectionA smooth, highly polished surface, such as amirror, alters the direction of a beam of lightwithout changing its form. The angle ofreflection is equal to the angle of inci-dence—a property that makes specularmaterials ideal where precise beam controlis desired (figure 9.1).

Because specular surfaces are virtuallymirrors, their own surfaces are almost invisi-ble; they may appear dark or bright, depend-ing on the observer’s position and on theluminance of the reflected image.

Semi-specular (spread) reflectionIrregular surfaces, such as those that are cor-rugated, hammered, brushed, sandblasted,or etched, partially disperse or “spread” thereflected beam. The greatest intensity, how-ever, is still reflected at an angle near theangle of incidence (figure 9.2).

Semi-specular materials appear withhighlights or streaks of higher brightness ona background of lower brightness. In interi-ors, they are often used as elements of spar-kle. In luminaires, semi-specular materialsproduce a moderately controlled beam thatis smooth and free from striations.

Diffuse reflectionRough or matte surfaces neutralize thedirectional nature of the incident beam.

105

9

Light is reflected from each point in all direc-tions, with maximum intensity perpendicularto the surface (figure 9.3).

Sand on the beach is an example of adiffuse reflecting surface. There are no brightspots; the surface appears the same from allangles of view. In interiors, this quality isoften desirable for walls, ceilings, and worksurfaces. In luminaires, diffusely reflectingmaterials are used to produce wide distribu-tions of light.

Reflector ContoursSpecular and semi-specular surfacesformed into geometric contours use the lawof reflection for beam control: the angle ofincidence equals the angle of reflection. Thisis the same law that governs the rebound ofa billiard ball off a cushion.

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Figure 9.2 Semi-specular (spread) reflection.

Figure 9.3 Diffuse reflection.

Figure 9.1 Specular reflection.

Figure 9.4 Elliptical contour.

Specular reflection is a primary tech-nique for modifying and controlling the direc-tion and distribution emitted by a lightsource. Specular reflection takes light thatwould otherwise be lost or wasted within aluminaire or emitted at glaring angles andconserves it by redirecting the light into aroom or onto a surface at useful angles.

In addition to this more efficient use oflight, the application of properly contouredreflectors produces predictable luminairedistributions and controlled room brightnesspatterns. Specular reflector contours com-monly used in luminaires include actual ormodified ellipses, parabolas, and circles.

Elliptical contourEllipses have two focal points; a ray of lightoriginating at one focal point is reflectedthrough the second focus. This produces adivergent beam; its spread depends on thedistance between the two foci (figure 9.4).Most downlights use reflectors with exact ormodified elliptical shapes. A special use ofthis contour produces a beam that passesthrough a small, inconspicuous openingflush with the ceiling plane.

Parabolic contourThe parabola is a special form of the ellipse,in which the two foci are far apart. A ray oflight originating at the exact focal point of aperfectly shaped parabolic contour is redi-rected in a direction parallel to the axis of thereflector, producing a beam of parallel rays(figure 9.5). The filament or source is neveran actual point; this results in a degree ofbeam-spread that depends on the size of thesource and the diameter of the reflector.

In its pure form, the parabolic contour isused for searchlights, spotlights, and direc-tional equipment where a concentrated beamand a limited spread of light are desired. Thebeam is often given additional spread bypassing it through a diffusing or refractinglens, as is done with many reflector lamps.

Circular contourThe circle is also a special form of theellipse, one where both foci are coincident; itis the opposite of the parabola. A ray of lightoriginating at the focal point of a circularcontour is reflected back through the samepoint (figure 9.6). It is used separately or incombination reflectors called compound

107

L I G H T C O N T R O L

Figure 9.5 Parabolic contour. Figure 9.6 Circular contour.

contours to redistribute light that would beotherwise misdirected or trapped.

Other reflector contoursCompound contours, which provide asym-metric distribution or maximum beam-spread with a shape of minimum dimension,are useful for producing uniformity of lumi-nance from a position close to the surfacebeing lighted; for example, to light the ceilingin a low-height room (figure 9.7).

Innumerable other possible reflectorcontours can be mathematically defined andtailored for a particular function. Thesereflectors do not have a specific focal point.

Reflectors

Specular reflectorsAlmost all reflector design presumes a com-pact “point” source of light or a linear sourceof light at the focus or other precise location.The most compact source is an incandes-cent filament in a clear bulb.

Large variations in beam control occur,however, with the use of lamps that emit

light from a larger area, such as an arc tubeor a phosphor-coated bulb or tube. In thesecases the bulb or tube, rather than the fila-ment, is the actual light source. This kind oflamp is both a large source displaced fromthe focus and a diffuse emitter. The result isa diffuse or less precisely defined beam anda reduced projection distance.

The first reflectors for electric luminaireswere designed by trial and error or by “long-hand” mathematics (figure 9.8). Today,computer-aided reflector design accountsfor all of the characteristics of a light sourceand optimizes a reflector contour.

Semi-specular reflectorsAlthough clear incandescent lamps in spec-ular reflectors produce efficient beam con-trol, there is often a need to smooth outirregularities in the beam. These striationsare reflected images of the filament coil.They are eliminated by a slight diffusion ofthe beam, accomplished by using (1) aninside-frosted lamp, (2) a lightly etched, fac-eted, or hammered reflector surface, or (3) amoderately diffusing lens in the beam path.

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Figure 9.7 Compound contour for maximum beam-spread (oftenused to produce asymmetric distribution).

Diffuse reflectorsThe reflection of light from a perfectly dif-fuse, flat surface is multidirectional, giving acircular distribution curve; the angle ofreflection is independent of the angle of inci-dence. With incident light dispersed in alldirections, the beam is wide (figure 9.9);because of this lack of directional control,long projection distances are impractical.

The shape of a diffuse reflector has littleinfluence on the resulting direction and dis-tribution of light. Diffuse reflectors are oftenuseful in luminaires that provide uniform,ambient brightness in a space, but they areunable to direct light toward a surface, suchas the workplane.

Reflector materialsAluminum is the material most frequentlyused for the fabrication of reflectors. It canbe stamped, spun, hydroformed, or extrudedinto almost any desired shape or contour; itcan be processed chemically and electricallyto make it more specular; and it can besandblasted or etched chemically to providevarying degrees of semi-specular reflection.

A hard, protective surface layer of hightransparency produced by the anodizing pro-cess prevents scratching and abrasion ofspecular aluminum surfaces and makescleaning practical.

TRANSMISSIONTransmission of light through a material isaffected by two things: (1) the reflections ateach surface of the material and (2) theabsorption and redirection within the mate-rial (called refraction; see page 111). Just asa continuous degree of reflection exists frommirrored, fully specular surfaces to matte,fully diffusing ones, a similarly continuousdegree of transmission exists from fullytransparent, clear materials to fully diffusing,translucent ones.

Direct transmissionTransparent materials leave the light distri-bution unchanged (figure 9.10). They areused as protective covers for absorbing orreflecting infrared or ultraviolet radiation orwhere a change in the color of light is desiredwhile maintaining the light distribution pro-

109


Figure 9.8 Parabolic reflector construction guide.


110

Figure 9.9 Diffuse reflector techniques.

duced by reflecting contours. Because thelight source remains visible, materials suchas clear glass and plastic are ineffective forglare control.

Semi-diffuse (spread) transmissionTranslucent materials emit light at widerangles because of configurations on at leastone side of the material (figure 9.11). Aslight redirection of the transmitted beam isachieved by minor surface irregularities,such as shallow facets or flutes, whichsmooth out imperfections and striations. Agreater degree of diffusion is achieved byetching, sandblasting, hammering, andmatte aerosol sprays applied to the outersurfaces; or the interior of the material ismodified to achieve the diffusion. Semi-dif-fuse materials provide lamp concealmentand glare control.

Diffuse transmissionDiffuse transmission disperses light in alldirections and eliminates the directionalquality of the beam (figure 9.12). Full diffu-sion is achieved by using opal glasses andplastics that incorporate microscopic parti-cles and remove all directionality from thetransmitted beam.

REFRACTIONWhen a straw is placed in a clear glass ofwater, it appears to bend at the point whereit enters the water. This is because thespeed of light changes when a light raypasses from air to water; the phenomenon iscalled refraction.

A similar result occurs when light passesfrom air to clear glass and plastics. Whenthese transparent materials are formed intoprisms or lenses, they become techniquesfor controlling the direction and, conse-quently, the distribution of light.

111


Figure 9.12 Diffuse transmission.

Figure 9.10 Direct transmission. Some first-surfacereflection occurs with all forms of transmission.

Figure 9.11 Semi-diffuse (spread) transmission.

112

Figure 9.14 Deviation with index of refraction.

Figure 9.15 Prismatic action.

Figure 9.16 A lens is a system of prisms.

Figure 9.13a and b The index of refraction is the ratio of the sines of the angles of incidence of a ray of light passing fromone medium (usually air) into another medium (such as water, glass, or plastic).

113


Figure 9.17 Convex lens.

Figure 9.18 Concave lens.

Figure 9.19 Fresnel lens.

PrismsA beam of light is displaced at the surface ofa transmitting material. If the material isformed with two parallel “faces,” the dis-placements neutralize each other; no angu-lar change in the direction of the beamoccurs, only a slight displacement (figure9.13a). If the opposite faces are not parallel,the unbalanced refraction permanentlyalters the direction of light (figure 9.13b).

Light rays deviate toward the perpendic-ular when entering a material with a higherindex of refraction and deviate away from theperpendicular when entering material with alower index (figure 9.14).

A prism is a transparent body boundedin part by two nonparallel faces. A beam of

light projected through one face is emitted ina different direction through another. By pro-viding the proper angle between prism faces,light is emitted in a desired direction (figure9.15).

LensesA lens is formed by two opposite refractingsurfaces, which have a common axis. It maybe thought of as a multiple array of prismswith a continuously changing included angleto produce an organized distribution of light(figure 9.16). Two basic kinds of lens sys-tems are used: convex and concave.

The convex (positive or converging) lensis thicker in the middle than it is at theedges. Its focal point lies on the axis, at the

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Figure 9.20 Distribution of light through a Fresnel lens.

point where the diverging rays from thesource are refracted to produce a parallelbeam of light (figure 9.17).

The concave (negative or diverging) lensis thinner in the middle than it is at theedges. This causes a parallel beam of light todiverge. The focus is called a virtual focalpoint; it is the artificial point at which thediverging rays would meet if they were tracedbackward as straight lines through the lens(figure 9.18).

Because refraction takes place at thesurface of the material, with the direction ofthe ray unchanged between surfaces, part ofthis transmitting material can be removedwithout affecting the optical control. Aconvex lens with sections of the glassremoved produces a lens that is thinner andlighter in weight.

The Fresnel lens, which is based on thisprinciple, consists of a series of concentriclens sections regressed into a planar array(figure 9.19). It is named for the Frenchphysicist Augustin Jean Fresnel (1788–1827), who developed the lens for use inlighthouses. In luminaires, the Fresnel lensproduces a concentrated beam of light whilealso reducing the brightness of the source,providing a degree of glare control.

The Fresnel lens has a short focallength. A light source located at this focusproduces a single, concentrated beam oflight with parallel rays. When the light sourceis positioned at points other than the primaryfocus of the optical system, the lamp-refrac-tor combination produces either a spread orasymmetric distribution (figure 9.20).

Glasses and plastics that incorporate aregular pattern of small prisms or otherrefractive elements are called prismaticlenses. They do not concentrate the distribu-tion of light the way Fresnel lenses do; pris-matic lenses spread the distribution of thesource but also reduce its luminance, pro-viding a degree of glare control.

Total Internal ReflectionTotal internal reflection occurs when lightpasses into a transparent medium, such asglass or plastic, at an appropriate angle andtravels inside the medium repeatedly reflect-ing from side to side. Edge lighting and lighttransmission through rods are examples ofthis phenomenon.

Fiber opticsWith fiber optics, light entering one side of aglass or plastic fiber of optical quality istransmitted to the other end by the processof total internal reflection. Light rays thatstrike the core at the acceptance angle arereflected back and forth inside the core andtravel to the other end of the fiber in a zigzagpath of successive reflections.

In use, a single, large-diameter fiber isimpractical because it lacks flexibility. Toincrease flexibility, a large number of small-diameter fibers are clustered together in abundle. In order to prevent light leaking fromone fiber to another, each is coated with atransparent sheath that has a lower refrac-tive index than the fiber (figure 9.21). Thesheathing process protects the surfaces ofthe fiber and allows the bundle to be embed-

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Figure 9.21 Enlarged section of optical fiber.

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Figure 9.22 Baffles.

Figure 9.23 Louvers.

117

Figure 9.24 Shielding angle.

Figure 9.25 Corrective solutions.

ded into other materials without loss of lightfrom the sides.

Optical fibers are combined in two kindsof bundles: coherent and incoherent. Coher-ent bundles contain fibers that are identi-cally positioned at the point of light entranceand light exit. Because each fiber conducts aportion of the light pattern to the same pointon the receiving end of a bundle, images canbe transmitted through the bundle. Incoher-ent bundles contain a random arrangementof fibers that can be used to transmit lightbut not images.

A typical fiber-optic lighting system con-sists of: (1) a light projector, (2) a tungsten-halogen or metal halide light source, (3) anoptical-fiber harness, (4) a fitting for each ofthe bundles, and (5) the bundles of opticalfibers themselves. Silicone rubber sheathinggives the bundles protection without loss offlexibility.

GLARE CONTROLSometimes the lens or reflector that is pro-viding the light control is also used toachieve concurrent glare control and lamp

concealment. At other times separate ele-ments are used.

Baffles and LouversBaffles and louvers shield glare at normalviewing angles, thereby contributing to visualcomfort.

Baffles provide shielding in one direc-tion, along a single axis (figure 9.22). Forsmall-aperture luminaires, a baffle around

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Figure 9.26 Transmitting materials: translucent white and colored plastic or glass, perforated metal. High-reflectancefinish: lightly etched metal, light wood, light-colored paint. Low-reflectance finish: matte black finish, dark wood finish,dark-colored paint.

Figure 9.27 Shielding as an aspect of contour design.

the perimeter provides shielding from alldirections.

Louvers are a series of baffles or shield-ing elements placed in a geometric patternto provide shielding from many directionswith minimum interference to the desiredbeam distribution (figure 9.23).

Shielding conceals the lamp and con-trols glare within a zone called the shieldingangle. This is the maximum angle that theeye is raised above horizontal without seeingthe light source beyond the shielding system(figure 9.24).

Although baffles and louvers concealthe light source from direct view within thisspecified zone, horizontal work surfaces arestill directly exposed to the source. The mir-rored image of the light source becomes asource of reflected glare from glossy paper,photographs, objects behind glass, and pol-ished tabletops (figure 9.25).

Baffles and louvers may be black ormade from reflective and transmitting mate-rials. The intensity of light directed towardthe eye is determined by the luminance ofthese surfaces. The choice of materials isbased on various considerations including

visual comfort and design harmony with thespace (figure 9.26).

To achieve concurrent glare control andlamp concealment with minimal change inthe diffuse beam, use open louvers, or plas-tic or glass with a slight degree of diffusion.Whether the beam is modified by diffusereflection or by diffuse transmission, the dis-tribution of light is the same.

ReflectorsAn opaque (light-blocking), concave reflec-tor also functions as a baffle, which shieldsthe light source. Additionally, the reflector’sshape affects the appearance of the visibleinterior surface. If light is redirected towardthe eye, the result is high luminance andunpleasant direct glare. If light is directeddownward and away from the eye, lumi-nance is reduced and glare is avoided.

In the most efficient reflector designs,source shielding is incorporated into thecontour design. This involves extending thereflector surface to provide the necessaryshielding (figure 9.27).

As reflector depth is increased, total effi-ciency is reduced because of absorption

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Figure 9.28 Parabolic reflector used for glare control. Figure 9.29 Parabolic reflector design for louvers andbaffles.

losses at the reflector surface. Because agreater portion of the emitted light is broughtunder control and redirected, however,candlepower and useful lumens increase.

Parabolic reflectors are often used forglare control. Little reflected luminance occursin the cross view of these reflectors becausemost of the light is directed downward withminimal light directed toward the eye; thisgives an impression of low brightness fromnormal angles of view (figure 9.28).

Diffusion of the reflector surface causesmore light to be directed toward the eye. As

a result, luminance is increased when reflec-tor surfaces are etched or brushed.

Parabolic reflector design is applied toboth reflectors and baffles. Figure 9.29shows the pattern of light reflections for lightrays originating above the louver. Ideally,light is reflected at an angle equal to theshielding angle.

Well-designed, specular, parabolic lou-vers provide equal or superior glare controlto matte-black or gray louvers, with greatersystem efficiency because of the reducedabsorption of light.

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PhotometricsIt is impossible to see a footcandle. What is seen is luminance, which is a

function of the amount of light falling on a surface and the reflectance of that

surface, modified by the surrounding conditions and adaptation of the eyes.

MEASUREMENT OF LIGHTPhotometry is the science that measureslight. Five terms are commonly used toquantify light: intensity, flux, illuminance,exitance, and luminance.

1. Intensity is the light emitted in a specificdirection by a source. Properly called lumi-nous intensity and defined as flux per solidangle in a given direction, it is measured incandelas (cd). Intensity in a succession ofdirections is plotted on a distribution curveor polar graph (figure 10.1).

2. Flux is the light emitted in all directionsby a source. Properly called luminous fluxand defined as time rate flow of light, it ismeasured in lumens (lm).

3. Illuminance is the density of light at anygiven point on a surface. Properly definedas density of flux incident on a surfacemeasured perpendicular to the surface, itis measured in footcandles (fc).

4. Exitance is the total quantity of lightemitted, reflected, or transmitted in all

directions from a surface. Properlydefined as density of flux leaving a sur-face, it is measured in lumens per squarefoot (lm/ft2).

5. Luminance is the accepted term for lightthat is reflected from a surface in a givendirection (back toward the eyes). Properlydefined as intensity of flux leaving a sur-face in a given direction, it is measured incandelas per square foot (cd/ft2).

Measurement LimitationsIlluminance is frequently used to measurethe quantity of light in architectural spacebecause it is the easiest and least expensiveunit to measure. Yet it is impossible to see afootcandle!

What is seen is luminance, which is afunction of the amount of light falling on asurface and the reflectance of that surface(its ability to reflect light). We see an objector surface only when light is reflected fromthat object or surface back toward the eyes,or when it is emitting light itself (self-lumi-nous).

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10

Brightness is what we perceive. It is asubjective attribute perceived in varyingdegrees of intensity. Reflected light was for-merly measured in footlamberts (fL).Because brightness changes with viewingangle, the term footlamberts has been dep-recated by the Illuminating Engineering Soci-

ety of North America (IESNA). Perceivedluminance is now measured by exitance.

It is only meaningful to measureexitance, however, if this quantity remainsconstant (or nearly so) for a wide range ofviewing angles. Diffuse surfaces, calledLambertian for the German physicist and

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Figure 10.1 Polar luminous intensity distribution curve.

philosopher Johann Heinrich Lambert (1728–1777), exhibit this property; thus, it is appro-priate to measure exitance only for Lam-bertian surfaces.

Calculations for illuminance (footcandlevalues) overlook the aesthetic, psychologi-cal, and physiological variables of the humanvisual process. When a convenient measureof perceived luminance becomes available,it will be more useful to calculate perceivedsurface luminance values, which account forthese factors.

The perception of surface luminance isbased largely on the eye’s ability to adapt.The iris dilates (opens) when illuminance islow and contracts (closes) when illumi-nance is high. It takes the eye longer toadapt from light to dark than from dark tolight. When you enter a dark theatre on asunny day, it takes twenty to thirty minutesfor the eyes to adapt completely to thelower illuminance. When you leave thetheatre and return to daylight, it sometimestakes only seconds for the eyes to adapt tothe higher luminance.

In a more subtle way, the eyes arecontinually adapting as you move in andthrough variously lighted spaces or lookaround at objects of varying illuminances.Even measured luminance does not indi-cate the apparent brightness because ofthe eye’s ability to adapt. Measured lumi-nance, then, yields a poor indication of per-ceived brightness, which is modified by thesurrounding conditions and adaptation ofthe eyes.

It is the balance of these relative lumi-nances, not the quantity of illuminancereceived on a surface, that determines suc-cessful lighting design. Therefore, theilluminance measurements that follow arenot to be used as the starting point for adesign. They are to be used only for lampand luminaire selection or to evaluate alighting design.

Luminous Intensity DistributionCurveThe intensity distribution curve representsthe amount of luminous intensity (cd) gener-ated in each direction by a light source in aplane through the center of the source. Con-sequently, the luminous intensity curve givesa picture of the total light pattern producedby a source.

Luminous intensity distribution curvesare available from luminaire manufacturersand are often found on the back of the man-ufacturer’s product data sheet. A polargraph is used to represent the distributionalintensity of a luminaire, and a rectilinear orCartesian graph to represent the distribu-tional intensity of a directional lamp.

In the polar graph (figure 10.1), theluminaire is located at the center of the radi-ating lines. The radiating lines represent spe-cific degrees of angular rotation from the 0°axis of the luminaire (nadir). The concentriccircles represent graduating intensityexpressed in candelas, with values enteredalong the vertical scale.

To determine the luminous intensity ofthis luminaire at 30°, find the appropriateangled line drawn from the center of theluminaire. Follow the line until it meets thepolar curve, then follow the circular line origi-nating at that point and read the luminousintensity (in candelas) on the vertical scale.In figure 10.1, the luminaire produces 1,850cd at 30° from nadir.

For luminaires with symmetrical lightdistributions, a single curve fully describesthe luminaire’s distribution. Often only oneside of the polar graph is shown, since theother side is an identical, mirror image.

A luminaire with an asymmetrical distri-bution, such as a linear fluorescent down-light, requires curves in a number of planesto adequately represent its distribution.Typically, one curve is parallel to theluminaire and another is perpendicular to

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P H O T O M E T R I C S

the luminaire; sometimes either a thirdplane at 45° or three planes at 22½° inter-vals are added (figure 10.2).

Reflector lamp sources or luminaireswith directional distributions and abrupt cut-offs, where the light intensity changes rap-idly within a small angular area, give valuesthat are difficult to read on a polar graph.Consequently, a rectilinear or Cartesiangraph is substituted to portray the candeladistribution (figure 10.3).

On this graph, the horizontal scale rep-resents the degrees from the beam axis andthe vertical scale represents the intensity incandelas. In the graph on the right of figure10.3, approximately 3,000 cd are producedby the light source at 10° from the beamcenter.

When selecting luminaires for a lightingapplication, be sure that the proposedluminaire and its source are precisely thoseshown in the manufacturer’s photometrictest data. It is inaccurate to extrapolate from

one source or reflector finish to anotherunless the photometric report includes mul-tipliers for various tested sources and reflec-tor finishes.

RECOMMENDED ILLUMINANCE VALUESIlluminance value recommendations arepublished as footcandles (fc) at the work-plane. For almost all commercial and indus-trial activities, this surface is considered tobe a horizontal plane 2 ft 6 in AFF (above fin-ished floor)—standard desk height—eventhough the space may be a corridor or a bas-ketball court with no desk in sight.

Remember that these values refer toilluminance on the horizontal work surfaceonly; they have limited significance to uswhen we interpret the actual environment.Such factors as wall lighting, brightnessaccents, shadow, sparkle, and color have agreater influence on emotional reaction.These factors are particularly important inareas involving casual seeing where low

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Figure 10.2 Polar graph for a fluorescent luminaire.

recommended illuminance values may bemisleading because a dull or gloomy envi-ronment will be unsatisfactory.

True illuminance requirements vary withthe visual difficulty of the work task, the ageand eyes of the worker, and the importanceof speed and accuracy in the completion ofthe task. Typical illuminance values areshown in table 15 in the Appendix. At best,these values provide a guide to the quantityof illuminance needed on the work surfacefor accurate and comfortable seeing.

In its Lighting Handbook, ninth edition,the IESNA publishes an illuminance selec-tion procedure with horizontal illuminancerecommendations for specific applications.It is supplemented by a “Design Guide” thatattempts to account for other factors thatinfluence perception: including the appear-ance of the interior, color appearance andcolor contrast, daylighting integration, glare,vertical illuminance, surface finishes andtextures, brightness contrast, facial model-ing, and the presence of sparkle.

A consolidated listing of the IESNA hori-zontal illuminance recommendations appearsin table 16 in the Appendix. It covers illuminancevalues for seven categories and a variety oftasks.

Categories A, B, and C include casualactivities that take place over the entire areaof a space. For example, in a circulationspace such as a hotel lobby or office buildingcorridor, the visual task of circulation is aconstant throughout the space, and anilluminance value of 5 fc is recommended.

Categories D, E, and F refer to commontasks that remain fixed at one or more partic-ular locations; these values are to be appliedonly to the appropriate task area, recognizingthat several different kinds of tasks may occurin the same room. The IESNA recommends avalue of 20 fc as the minimum illuminance onthe horizontal work surface for the “non-task”parts of the room where less demandingvisual work is performed.

Category G is for special, visually difficulttasks. The lighting system for these tasksrequires careful analysis. Recommendedilluminance values are achieved with supple-mental task lighting, and range from 300 to1,000 fc.

AgeIESNA illuminance recommendations do notaccount for the age of the occupants. Thevisual requirements of older persons differ

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Figure 10.3 Rectilinear luminous intensity distribution curve of a 60PAR38/HIR spot lamp (left) and a 60PAR38/HIR floodlamp (right).

from those of younger persons in two ways:(1) the lens of the eye thickens, decreasingthe eye’s ability to change its shape to prop-erly focus at varying distances (figure 1.6),and (2) pupil size becomes reduced, decreas-ing the amount of light reaching the retina.

Older persons require higher illuminancevalues for the same tasks (a sixty-year-oldrequires three times the illuminance of atwenty-year-old for equal retinal illumi-nance). At the same time, glare sensitivitywithin the field of view is significantlyincreased.

IESNA illuminance recommendationsassume an age of forty to fifty-five. As a rule-of-thumb, for persons under age forty,illuminance values may be reduced by up toone-third; for persons over age fifty-five,illuminance values may be increased by upto two-thirds.

ILLUMINANCE CALCULATIONSAlthough people see not footcandles butluminance contrast, the question of howmuch light is necessary for tasks must stillbe answered. Calculations are performedduring the design process to obtain informa-tion about lamp and luminaire performance,to evaluate design alternatives, or to refine aparticular design.

Following are descriptions of simple cal-culation methods, with examples for deter-mining illuminance at a specific point andthe average illuminance on a specific plane.

Illuminance at a PointTo find the value of incident illuminance at aspecific point produced from a compactsource, the inverse-square method is used.This method closely approximates the illumi-nation where the distance from the source isat least five times the maximum dimensionof the source.

Source aimed at a targetIlluminance is proportional to the luminousintensity of the source in the given direction,and inversely proportional to the square ofthe distance from the source.

To calculate illuminance (fc) from asource aimed at a surface perpendicular tothe source:

fc = ID2

where I is the intensity of the source (in can-delas) in the direction of the point and D isthe distance from the source to the point(figure 10.4).

ExampleA 60PAR/HIR/SP10 lamp is aimed at a pointon a surface 12 ft away. From a luminousintensity distribution chart (figure 10.3, left),find that the 60PAR/HIR/SP10 lamp pro-duces 20,000 cd at 0°:

fc =20,000

122= 139

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Figure 10.4 Illuminance on a surface perpendicular tothe source.

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Figure 10.5 Illuminance on a horizontal surface—source at an angle.

Figure 10.6 Illuminance on a horizontal surface—target located to one side of a source at nadir.

Figure 10.7 Illuminance on a vertical surface—sourceat an angle.

Figure 10.8 Illuminance on a vertical surface—targetlocated to one side of a source at nadir.

Source aimed at an angle to ahorizontal surfaceIf the source is aimed at an angle toward thetarget instead of being perpendicular to thetarget, the light will spread over a greaterarea, reducing the illuminance at a specificpoint. For a horizontal surface, the reductionis equal to the cosine of the angle of inci-dence or “tilt.”

To calculate illuminance from a sourceat an angle to a horizontal surface:

fc = ×ID2

cos θ

where I is the intensity of the source (in can-delas) in the direction of the light ray, θ is theangle of tilt between nadir and the directionof the light ray, and D is the distance fromthe source to the target surface (figure10.5).

In figure 10.5, H is the vertical mountingheight of the light source above the target ofmeasurement, and R is the horizontal dis-tance (run) from the light source to thetarget.

ExampleA 60PAR/HIR/SP10 lamp is tilted at 30° fromnadir (straight down) to cast light on a hori-zontal surface 12 ft away (D). To determineilluminance on the surface, follow thesesteps:

1. From an intensity distribution chart (figure10.3, left), find that the 60PAR/HIR/SP10lamp produces 20,000 cd at 0° (thedirection of the ray).

2. From the table of trigonometric functions(table 10 in the Appendix), find that thecosine of 30° is 0.866.

fc =20,000

12.866

2× =0 120

Source at nadir, target onhorizontal surface locatedto one sideIf the source is aimed straight down but thetarget is located to one side of the centralray, the illuminance at the target on a hori-zontal surface will be the intensity of thebeam at nadir reduced by the cosine of theangle from the source to the target.

To calculate illuminance from a source atnadir to a point located to one side on a hori-zontal surface, the same formula is used:

fc = ×ID2

cos θ

where I is the intensity of the source (in can-delas) in the direction of the light ray, θ is theangle between nadir and the direction of thetarget, and D is the distance from the sourceto the target surface (figure 10.6).

ExampleA 60PAR/HIR/FL30 lamp is pointed straightdown. To determine the illuminance at atarget that is 10° to one side of nadir on ahorizontal surface 12 ft away, follow thesesteps:

1. From an intensity distribution chart (figure10.3, right), find that the 60PAR/HIR/FL30 lamp produces 2,800 cd at 10°(the direction of the ray).

2. From the table of trigonometric functions(table 10), find that the cosine of 10° is0.985

fc =2,80012

.9852

× =0 19

Source aimed at an angle to avertical surfaceIf the source is aimed at an angle toward atarget on a vertical surface, the reduction in

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illuminance at the target is equal to the sineof the angle of incidence or tilt.

fc = ×ID2

sin θ

where I is the intensity of the source (in can-delas) in the direction of the light ray, θ is theangle of tilt between nadir and the directionof the target, and D is the distance from thesource to the target (figure 10.7).

In figure 10.7, H is the vertical mountingheight of the light source above the targetand R is the horizontal distance (run) fromthe light source to the target.

ExampleA 60PAR/HIR/SP10 lamp is tilted at a 30°from nadir to cast light on a vertical surface6 ft away. To determine illuminance on thesurface, follow these steps:

1. From an intensity distribution chart (figure10.3, left), find that the 60PAR/HIR/SP10 lamp produces 20,000 cd at 0°(the direction of the ray).

2. From the table of trigonometric functions(table 10), find that the sine of 30° is0.500

fc =20,000

12.500

2× =0 69

Source at nadir, target on verticalsurface located to one sideIf the source is aimed straight down but avertical target is located to one side of thelight ray, the illuminance at the target on thevertical surface will be reduced by the sine ofthe angle between nadir and the target.

To calculate illuminance from a sourceat nadir to a target located to one side on avertical surface, the same formula is used:

fc = ×ID2

sin θ

where I is the intensity of the source (in can-delas) in the direction of the light ray, θ is theangle between nadir and the direction of thetarget (to one side), and D is the distancefrom the source to the target surface (figure10.8).

ExampleA 60PAR/HIR/FL30 lamp is pointed straightdown. To determine the illuminance at atarget that is 10° to one side of nadir on avertical surface 12 ft away, follow thesesteps:

1. From an intensity distribution chart (figure10.3, right), find that the 60PAR/HIR/FL30 lamp produces 2,800 cd at 10°(the direction of the ray).

2. From the table of trigonometric functions(table 10), find that the sine of 10° is0.174.

fc =2,80012

.1742

× =0 3

ShortcomingsThe inverse-square method yields only arough idea of what is perceived. Its chief useis for comparison, as when establishing theilluminance ratio between an object and itssurround. Even here, the inverse-squaremethod fails to account for any inter-reflections within the space. And more sig-nificantly, perceived brightness depends onthe reflectance of the surface and the posi-tion of the observer.

Average Illuminance CalculationsTo ensure that adequate illuminance is pro-vided over a large area, the lumen method,or zonal-cavity calculation, is used. This cal-culation is performed by hand or generatedby computer; it predicts the averageilluminance incident on a horizontal worksurface, usually the workplane.

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For a rough estimate of the averageilluminance on a horizontal surface, theabbreviated version of the lumen methoddescribed below will suffice. It considersboth the interreflections of light from roomsurfaces and the contributions of severallight sources. It corrects for maintainedilluminance, accounting for typical deprecia-tion in lamp lumens over the life of thesource and for dirt accumulation on theluminaire surfaces.

This shorthand method is not a substi-tute for more precise illuminance calcula-tions. It is merely a guide to be used as aquick analysis during the design process.

To calculate the average maintainedilluminance falling on a horizontal surface,

fc =Number of lamps Initial lamp lumens LLF CU

Area× × ×

Number of lamps. For single-lamp lumi-naires, the number of lamps equals thequantity of luminaires in a given area. Ifthe luminaires contain more than onelamp, multiply the number of luminairesby the number of lamps per luminaire.

Initial lamp lumens. The initial lamp lumensare published by the lamp manufactur-ers in their large-lamp catalogs.

LLF is an abbreviation for light loss factor. As asystem ages, a natural depreciation inlight output occurs. (With tungsten-halogen lamps, the loss is negligible.)Also, dust and dirt accumulate on roomand luminaire surfaces. Other light lossfactors such as ambient temperature,actual input voltage, ballast factor, HIDlamp position, and lamp burnouts influ-ence the illuminance in a space; for thisquick method, only two are considered:LLD and LDD.

• LLD is an abbreviation for lamp lumendepreciation. This is the amount of

light output that is reduced over thelife of the lamp because of filamentevaporation, tungsten deposits on thebulb wall, and phosphor degradation.

A list of lamp lumen depreciationfor many sources is found in table 11in the Appendix. When mean lamplumens (sometimes called “designlumens”) are listed in the lamp cata-log, this value may be used directly inthe formula without the LLD factor.

• LDD is an abbreviation for luminairedirt depreciation. This is the reductionof light output over time owing to theaccumulation of dust and dirt on thereflecting and transmitting surfaces ofthe luminaire. This figure is dependenton the cleanliness of the space, thefrequency of luminaire cleanings, andthe luminaire’s tendency to collect dirt(for example, open-top luminaireshave a greater ability to collect dirtthan closed-top luminaires; someluminaires have a ventilation patterndesigned so that the flow of air slowsthe accumulation of dust). See tables12 and 13 in the Appendix.

With this method, LLF = LLD × LDD.Typical light loss factors for open light-shielding systems (such as louvers) are0.85 for very clean spaces, 0.75 forclean spaces, 0.65 for medium spaces,and 0.55 for dirty spaces.

CU stands for coefficient of utilization. TheCU is an expression of the percentage oflight output that is expected from a spe-cific luminaire in a room. It accounts forthe efficiency of the luminaire: its abilityto deliver light to the work surface com-pared to the lumens supplied by thelamp(s). This is the amount of light thatis not trapped and lost inside theluminaire.

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The CU also accounts for the efficiencyof the room in redirecting and inter-reflecting the incident light that strikes itssurfaces. This is affected by the room’sproportions as well as its reflectances. Alarge, low room is more efficient than atall, narrow one. In the large, low room,little incident light is interrupted by thewalls; almost all of the light is receiveddirectly by the workplane. In a high,narrow room, much of the incident lightstrikes the walls at least once beforereaching the workplane, sometimesbeing reflected between several sur-faces before reaching the task.

These variables produce an infinitenumber of CUs for each luminaire. For prac-tical purposes, they are reduced to a groupof figures for typical room proportions andreflectances.

Room Cavity Ratio. The CU is found bychecking the manufacturer’s coefficient-of-

utilization table, which is usually publishedon the back of product data sheets. In orderto use the CU table, it is first necessary tocalculate the room cavity ratio.

The room cavity ratio provides anexpression of the efficiency of room propor-tions. To determine this ratio:

RCR = +×

5( )( )h l wl w

where h is the height of the ceiling above thetask surface, l is the length of the room, andw is the width of the room. The task surfaceis usually considered to be 2 ft 6 in AFF(above finished floor) (figure 10.9).

A sample coefficient of utilization tablefor a compact fluorescent, open-reflectordownlight is shown in table 14 in the Appen-dix.

ExampleCalculate the average maintained illumi-nance on the workplane in a 15 ft × 30 ft

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Figure 10.9 The room cavity used in the abbreviated lumen or zonal-cavity method.

office with an 8 ft ceiling and a regulararrangement of eight luminaires; eachluminaire uses two 26 W compact fluores-cent lamps.

fc =Number of lamps Initial lamp lumens LLF CU

Area× × ×

1. The number of lamps (2 lamps perluminaire × 8 luminaires) is 16.

2. From a large-lamp catalog, find that theinitial lumens for a 26 W compact fluo-rescent lamp are 1,800 lm.

3. LLF = LLD × LDD.

a. LLD: in table 11, under fluorescent,compact, find that the lamp lumendepreciation factor is 0.85.

b. LDD: in table 12, find that a directdownlight with an opaque, unaper-tured top enclosure and without abottom enclosure is maintenancecategory IV. In table 13, a very cleanroom that will have its luminairescleaned every six months yields aluminaire dirt depreciation factor of0.96.

c. 0.85 × 0.96 = 0.82.

4. To find the coefficient of utilization, firstcalculate the room cavity ratio:

a. h = ceiling height of 8 ft 0 in minusdesk height of 2 ft 6 in = 5 ft 6 in(5.5 ft).

RCR

5.52.75

= +×

= + =

5

5 15 3015 30

( )( )

( )( )( )( )( )

h l wl w

b. In table 14, which is supplied by themanufacturer of this compact fluo-

rescent, open-reflector downlight,find that for a room with 80% ceilingreflectance, 50% wall reflectance,20% floor reflectance, and an RCR of3, the CU is 0.68.

fc =(16)(1,800)(0.82)(0.68)

(15)(30)= 36

This office, lighted by eight, two-lamp,26 W, compact fluorescent, open-reflectordownlights, will have an average maintainedilluminance of 36 fc on the desk. Althoughthe lumen method does not demonstrate it,in all spaces the illuminance value is higherin the center of the room and drops off nearthe walls because of the absorption of theperimeter surfaces.

ShortcomingsWhether executed by hand or calculated bycomputer, the lumen method fails to providethe range of light intensity in a room andidentify where differences in illuminancevalues occur. It is, therefore, inaccurate fornonuniform and task-ambient lighting sys-tems.

This method is also unable to provideinformation about lighting quality, visualcomfort, and luminance patterns. The lumenmethod is useful mainly for predicting hori-zontal illuminance with general lighting sys-tems.

Computer AssistanceThe complete zonal-cavity method is foundin the ninth edition of the IESNA LightingHandbook, Chapter 9, and is available ondisc from several software companies foruse with a personal computer.

Computer-generated point calculationsyield illuminance at selected points through-out a room. They also provide average, maxi-mum, minimum, and standard deviation of

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illuminance values; room surface luminances;and lighting power density (watts/ft2). Outputis usually a chart of calculated values, anisofootcandle plot, or a shaded plan withgray scales representing the range ofilluminance values. This software can modelreflections only from perfectly diffuse sur-faces, however, although this is adequate formost lighting calculations.

Computer-generated ray-tracing calcu-lations are the most accurate method ofcomputing illuminance. By tracing each“ray” of light, realistic depictions ofilluminance patterns on room surfaces, par-titions, furniture, and artwork are displayed,including reflection from specular surfacesand refraction by transparent objects.Output is in the form of renderings or videoimages. Hardware requirements for this kindof program are greater than for other meth-ods; at a minimum, a personal computerwith powerful graphics capabilities is neces-sary.

The IESNA publishes an annual surveyof lighting software in its magazine LightingDesign + Application. Products are reviewedfor analysis features, applications, outputs,user features, hardware requirements, andcosts.

SURFACE REFLECTANCEAlthough interior surfaces are not light con-trol devices, their reflectance properties arefundamental to the lighting design. Thequantity and direction of light reflected fromthese surfaces affect both the efficiency ofthe initial light distribution and our percep-tion of surface brightness.

Wall, ceiling, and floor surfaces arelarge-area “reflectors” that redistribute lightin the room. High-reflectance finishes, suchas white and off-white, promote maximum

use of the available light; increasingly darkerfinishes intercept and absorb increasinglygreater proportions of the light.

Because a useful amount of light reachesthe workplane after reflection from the wallsand the ceiling, the efficiency of the lightingsystem depends in part on the reflectance ofroom surfaces and finishes. This is particu-larly true of ambient-diffuse and indirect sys-tems, where a large portion of the light isinitially directed toward the ceiling or thewalls or both.

In task-oriented spaces such as offices,factories, or cafeterias (where the “task” isseeing the food and the people), the follow-ing surface reflectances are recommendedfor the efficient use of light:

20–50% floor50–70% wall70–90% ceiling

The illuminance values in tables 15 and16 in the Appendix presume that commer-cial reflectances are:

20% floor50% wall80% ceiling

and presume that industrial reflectances are:

20% floor50% wall50% ceiling

The recommended reflectances for fur-niture, machinery, partitions, and work sur-faces are the following:

25–45% furniture and machinery25–50% work surfaces

Room surface finish reflectances areobtained from the manufacturers of paints,

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wall coverings, ceiling tiles, floor coverings,furniture, and machinery. The following roomreflectances are a guide:

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white, off-white, gray, light tints of blue or brown 75–90%

medium green, yellow, brown, or gray 30–60%

dark gray, medium blue 10–20%

dark blue, brown, dark green, and many wood finishes 5–10%

ElectricityKnowledge of the basic principles of electricity is necessary for understanding

lighting circuitry, electrical distribution, power consumption, operating costs,

switch control, and dimming control.

PRINCIPLES OF ELECTRICITYElectrically charged particles called elec-trons, which orbit the nucleus of an atom,can be made to flow from one point toanother. This is observable in objectscharged by friction and in natural phenom-ena: lightning is a huge spark of electricity.

A flow of electricity is called an electriccurrent; the rate of flow of an electric currentis measured in amperes (amps, A). Thepotential of the flow of electricity is called volt-age; it is measured in units called volts (V).

Water provides a helpful analogy tothese concepts. The amount of pressurethat moving water exerts inside a pipe isanalogous to volts; amperes are similar tothe “gallons-per-second” measurement, therate at which water passes through the pipe.The pipe is the conductor or wire, the wall ofthe pipe is the insulator, and the faucet isthe resistance or dimmer. The larger thepipe, the greater the flow it can carry.

The path through which an electric cur-rent flows is called a circuit. When no gapexists in the path, it is called a complete cir-cuit (figure 11.1). When a gap occurs, it iscalled a break in the circuit.

Resistance impedes the flow of currentand is determined by the composition of amaterial. This results in the production oflight or heat or both. A resistor is a deviceplaced in the path of an electric current toproduce a specific amount of resistance. Ifelectricity flowing along a path is slowed by

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11

Figure 11.1 Complete circuit.

resistance or interrupted by an open switch,there will be little or no current (amps) eventhough the potential to produce it (volts) ishigh.

WiringMaterials that electricity flows easily throughare called conductors. Materials throughwhich it does not flow easily are called poorconductors, or insulators. All metals aregood conductors: silver is the best conduc-tor, but it is too costly for most wiring pur-poses; copper is an excellent conductor andis used widely.

Almost all wire is encased within aninsulator, which confines the current to itsmetallic conductor. Wire that is wrappedwith a poor conductor, such as rubber orsynthetic polymers, is called insulated wire.Before connections are made with insulatedwire, the wrapping is removed from the endsof the wire.

Insulated circuit wires are sometimescovered by a mechanically protective con-duit for installation in buildings. Flexible,nonmetallic sheathed cable (“romex”) andflexible, metal sheathed cable (“BX”) areoften used in single-family homes. Commer-cial installations use wires inserted in flexiblemetal conduit (“greenfield”), or in rigid elec-trical metal tubing (“EMT”) for long runs.

CircuitsDirect current (dc) is electric current thatalways flows in one direction. Alternatingcurrent (ac) also moves in a single direction;however, that direction is reversed at regularintervals. Alternating current is the prevailingelectrical current in use today (figure 11.2).

A cycle includes the complete set ofvalues through which the alternating currentpasses. The unit Hertz (Hz) is used to mea-sure the number of times the cycle occurseach second, which is also called the fre-quency of the cycle. Power distribution sys-

tems operate at 60 Hz in the United Statesand 50 Hz in most other parts of the world.

Series circuitIf one lamp fails in an inexpensive strand ofChristmas tree lights, the remaining lamps inthe strand go out. When the tungsten wire inone lamp breaks, it causes a break in the cir-cuit because its filament is part of the con-ductive path carrying current to other lamps.

Lamps connected in this way are wiredin series. All lamps in a series circuit must beof the same wattage; if a lamp of differentwattage is substituted, the remaining lampswill grow brighter or dimmer due to the sub-stituted lamp’s resistance. A series circuit istherefore said to be load-sensitive (figure11.3).

Parallel circuitIf one lamp in figure 11.4 goes off, all of theothers remain lighted; the current still flowsto the other lamps and the circuit remainscomplete. These lamps are wired in parallel.Since the voltage of the circuit is presentacross all branches of the circuit, several dif-ferent loads (for example, a 60 W lamp anda 100 W lamp) may be connected to the

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Figure 11.2 Alternating current.

same circuit. Parallel circuits are thereforenot load-sensitive.

A current will always follow the easiestpath that is available. If the wires of a circuitare uninsulated and touch each other, thecurrent will pass from one to the otherbecause this is a shorter and easier paththan the one intended: there will be a shortcircuit.

In the drawing on the left in figure 11.5,the current will take a shortcut back to thecell without going through the push button;the bell will ring continuously whether theswitch is open or closed. In the drawing onthe right, the bell will not ring at all; the cur-rent will take a shortcut back to the cell with-out going through the bell.

A short circuit allows a stronger-than-usual flow of electricity through the wires;this excessive current causes the wires tooverheat. A fuse or circuit breaker is a safetydevice that opens the circuit before the wirebecomes a fire hazard. Because the fuse ispart of the circuit, it also overheats and ametal strip in the fuse melts and breaks thecircuit. If the protective device is a circuitbreaker, the excess current of the short cir-cuit causes the breaker to flip open, inter-rupting the path of the current.

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E L E C T R I C I T Y

Figure 11.3 Series circuit.

Figure 11.4 Parallel circuit.

Figure 11.5 Two short circuits. The wire in these circuits isbare wire. Where the wires are twisted together, the currentwould flow from one to the other.

Electrical DistributionElectric current generated and delivered byan electric utility enters a building through aservice panel. In the United States, threekinds of systems are common:

1. 120/240 V, single-phase, three-wire.

2. 120/208 V, three-phase, four-wire.

3. 277/480 V, three-phase, four-wire.

The 120/240 V, single-phase, three-wire system is commonly used in single-family homes and small commercial build-ings. Wire conductors leading from theentrance panel distribute the power through-out the building. Because the wire has resis-tance, the longer the distance that power iscarried, the greater the voltage losses, caus-ing lights to dim and appliances to operatesluggishly. This is corrected by using larger-diameter wires, which have less resistance.

Distributing current at higher voltagesreduces losses occurring because of thewire’s resistance. Therefore, in large com-mercial buildings, 120/208 V, three-phase,four-wire and 277/480 V, three-phase, four-wire systems are used to reduce resistancelosses.

In commercial buildings, running eachcircuit from the entrance panel will create asubstantial voltage loss or require the use oflarge-diameter, expensive wires. To avoidvoltage loss, feeder circuits conduct powerfrom the entrance panel to secondary distri-bution panels, called panel boards, locatedthroughout the building. The wires that dis-tribute power locally between the panelboard and the luminaires or receptacles arecalled branch circuits.

Power ConsumptionA watt (W) indicates the rate at which elec-tricity is changed into another form of

power—light or heat. Power consumption inwatts is calculated by multiplying volts timesamps (W = V × A).

Theoretically, a 20-amp circuit operat-ing at 120 V will handle a possible maximumload of 2,400 W (that is, 20 × 120 =2,400). In practice, the National ElectricalCode limits the possible load of a branch cir-cuit to 80 percent of the branch circuitampere rating: a 15 A, 120 V circuit to1,440 W; a 20 A, 120 V circuit to 1,920 W;a 20 A, 277 V circuit to 4,432 W.

Energy is the amount of electric powerconsumed over a period of time; it is mea-sured in kilowatt-hours (kWh). One kilowatt(kW) = 1,000 W. Hence, kWh = kW ×hours used. For example, a 150 W lamp isequivalent to 0.15 kW. When operated for40 hours it uses 6 kWh (0.15kW × 40 hrs =6 kWh). Utility rates are based on monthlykWh usage.

In estimating the connected load for dis-charge and low-voltage incandescent sources,the power consumed by the ballast or trans-former must be included.

To obtain lighting watts per square footfor an installation, divide the total luminairewatts by the area of the space in square feet.

Life Cycle CostsThe cost of lamps and luminaires plus theirinstallation is a minor part of the total costover the life of a lighting system. The cost ofelectricity (operating costs) is the single larg-est cost in lighting. Except in homes, mainte-nance (labor costs) to replace lamps andclean luminaires is the second greatestexpenditure. Lighting systems, therefore,must be evaluated in terms of life cycle costs.

A typical cost analysis will include initiallamp and luminaire costs; installation costs;electricity costs based on burning hours peryear; labor costs, including those incurredbecause of dirt conditions; and interestcosts on the original capital investment.

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When comparing the life cycle costs of onesystem with those of another, the greater ini-tial cost of an energy-effective system willalmost always be recouped after a period oftime because of the saving in energy costs.This payback period varies with different sys-tems.

In comparing dissimilar systems, it isimpossible to place a dollar value on thequality of light. A direct system, for example,is usually less costly than an indirect onethat produces the same quantity of light on ahorizontal workplane, but the quality of lightis vastly different.

Cost comparisons are made on equalilluminance values of equivalent quality. Ifthere is a difference in the connected load,the additional air-conditioning required tohandle the larger load must also be counted.

SWITCH CONTROLAn electric current is the flow of electronsbetween two points along a path. If the pathis interrupted, the current cannot flow. Aswitch breaks the flow of electricity in a cir-cuit when it is open (“off”) and it allowsunimpeded flow when closed (“on”).

Manual SwitchesThe manually operated toggle switch makescontact by snapping one metal piece againstanother. Mercury switches contain a vial ofmercury; contact is made between two elec-trodes when the vial is tripped to the “on”position. These switches operate silently.The toggle designates “on” in the up positionand “off” in the down position. A rockerswitch and a push-button switch operate inthe same manner (figure 11.6).

A single-pole, single-throw switch isconnected at any point between theluminaire and the power supply. It opensonly one side of the circuit and is thereforecalled a “single-pole”; it moves only betweenan open and a closed position and is there-fore called a “single-throw.” This is theswitch most frequently used to control elec-tric luminaires and wall receptacles.

A single-pole, double-throw switchdirects the current in either of two directions.It is used to alternately turn on two differentluminaires with a single switch action, suchas a safelight and the general light in a dark-room. The up position will designate “on” forone luminaire, the down position “on” for the

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Figure 11.6 Toggle switch and rocker switch.

other; an optional center position will turnboth “off.”

A double-pole, single-throw switch isable to direct the current to two paths atonce. It is used to control two devices simul-taneously, such as a luminaire and anexhaust fan; it functions as if two separatetoggle switches were operated by the samehandle.

A three-way switch controls an electricalload from two locations. This allows the cir-cuit to use one of two alternate paths tocomplete itself. (Several explanations existfor why a switch that provides control fromtwo locations is called “three-way.” Althoughthese explanations are hypothetical andflawed, the term is still customary.)

A four-way switch controls a circuit fromthree locations, a five-way switch controls acircuit from four locations, and so forth. Forcontrol from many different locations, a low-voltage switching system is used.

TimersA timer automatically turns on electric light-ing when it is needed and turns it off when itis not needed. Timers range in complexityfrom simple integral (spring-wound) timersto microprocessors that can program asequence of events for years at a time. Witha simple integral timer, the load is switchedon and held energized for a preset period oftime, usually within a range between a fewminutes and twelve hours.

An electromechanical time clock is drivenby an electric motor, with contacts actuatedby mechanical stops or arms affixed to theclock face. Electronic time clocks provide pro-grammable selection of many switching oper-ations and typically provide control over aseven-day period. Electromechanical andelectronic time clocks have periods fromtwenty-four hours to seven days and ofteninclude astronomical correction to compen-sate for seasonal changes.

Occupancy SensorsOccupancy sensors (also called motion sen-sors) automatically switch luminaires on andoff to reduce energy use. They operate inresponse to the presence or absence ofoccupants in a space. Electrical consump-tion is reduced by limiting the number ofhours that luminaires remain in use.

Occupancy is sensed by one of fourmethods: audio, ultrasonic, passive infrared,or optical. Occupancy sensors can bemounted in several ways: they can berecessed or surface-mounted on ceilings,corners, or walls; they can replace wallswitches; and they can plug into recepta-cles. The floor area covered by individualsensors can range from 150 sq ft in individ-ual rooms, offices, or workstations to 2,000sq ft in large spaces. Larger areas are con-trolled by adding more sensors.

Occupancy sensors can be used in com-bination with manual switches, timers, day-light sensors, dimmers, and central lightingcontrol systems. Careful product selectionand proper sensor location are critical toavoid the annoying inconvenience of falseresponses to movement by inanimateobjects inside the room or people outsidethe entrance to the room.

PhotosensorsPhotosensors (also called daylight sensors)use electronic components that transformvisible radiation from daylight into an electri-cal signal, which is then used to control elec-tric lighting. The photosensor comprisesdifferent elements that form a completesystem. The word “photocell” (short for“photoelectric cell”) refers only to the light-sensitive component inside the photo-sensor. The term “photosensor” is used todescribe the entire product, including thehousing, optics, electronics, and photocell.

The photosensor output is a controlsignal that is sent to a device that controls

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the quantity of electric light. The controlsignal can activate two modes of operation:(1) a simple on-off switch or relay, or (2) avariable-output signal sent to a controllerthat continuously adjusts the output of theelectric lighting.

Different photosensors are manufac-tured for indoor or outdoor use. In the north-ern hemisphere, photosensors used inoutdoor applications are usually oriented tothe north. This orientation ensures moreconstant illumination on the sensor becauseit avoids the direct sunlight contribution.

Wireless Remote Control

Radio-controlled systemsSome systems allow wireless remote controland can interface to audiovisual and othersystems in both commercial and residentialapplications. Radio-controlled systems elim-inate the need for wiring between thesensor, processor, and controller. Radiotransmitters communicate with controllersvia radio frequency (RF) signals. Controllers,in turn, regulate and adjust electric lighting.These systems can employ multiple trans-mitters for multiple-location control andmultiple controllers for multiple areas.

Radio frequencies from many sourcescan interfere with proper operation of thisequipment, however. These systems arealso relatively expensive, but they are usefulwhere the controlled luminaires are difficultto access. They are also suited to retrofitapplications where control wiring would bedifficult or expensive to install.

Infrared preset controlsInfrared preset controls allow you to createand recall settings for electric lighting thesame way you set and recall AM and FM sta-tions on a stereo tuner/receiver. The hand-held remote control sends an infrared (IR)signal to wall-mounted switches and dim-

mers that have a receiving IR window. Anunlimited number of dimmers may be con-nected in the same room.

Typically, infrared preset controls havean IR range of up to 50 ft along the line ofsight. They use standard wiring and can beretrofitted to replace switches or dimmers,using the existing wires for installation.Good-quality infrared controls will minimizechances of interference from radio, audio,and video equipment.

DIMMING CONTROLA dimmer provides variation in the intensityof an electric light source. Full-range dim-ming is the continuous variation of lightingintensity from maximum to zero without visi-ble steps.

All dimming systems operate on one oftwo principles for restricting the flow of elec-tricity to the light source: (1) varying the volt-age or (2) varying the length of time that thecurrent flows during each alternating currentcycle.

Resistance DimmersHistorically, resistance dimmers were thefirst dimming method; they were usedmainly in theatres in the early part of thetwentieth century. A resistance dimmer, or“rheostat,” controls voltage by introducinginto the circuit a variable length of high-resistance wire. The longer the length of thewire, the greater the resistance, the lowerthe voltage, and the lower the intensity ofthe lamp.

In order to absorb a sufficient amount ofenergy, the resistance wire must be quitelong; for this reason it is often coiled. Currentflows into one end of the coil and an armslides along the resistance wire in incre-ments. Dimming is thus achieved in a seriesof steps, often a minimum of 110 to appear“flicker-less.”

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A large drawback to this kind of dimmeris that the portion of the current that wouldotherwise produce light is instead convertedto heat. Also, no savings in energy is real-ized: although light output is reduced, con-nected wattage remains unchanged. Inaddition, these dimmers are bulky; conse-quently, they are no longer used.

Autotransformer DimmersAutotransformer dimmers avoid these prob-lems by using an improved method of dim-ming. Instead of converting the unusedportion of the current into heat, theautotransformer changes the standard-volt-age current into low-voltage current, withonly a 5 percent power loss.

A transformer has two coils of wire; theratio of the number of turns in one coil to theother produces the ratio of the voltagechange induced by the transformer. Anautotransformer is simply a variable trans-former: the primary coil remains fixed, whilethe number of turns in the secondary coil is

varied by a rotating arm that controls suc-cessive turns of the coil. Because electricalpower can be drawn from different pointsalong the secondary coil, different voltagesare achieved from the same transformer.

Because autotransformers do not con-vert energy to heat as light intensity isreduced, they are therefore cooler andmore compact than resistance dimmers.Autotransformer dimmers are widely avail-able in sizes up to many thousands ofwatts.

Solid-State DimmersSolid-state dimmers are predominant today;they use the second of the two methods oflimiting current flow. A power control device—such as a silicon-controlled switch (SCS)under 6 kW, or a silicon-controlled rectifier(SCR) over 6 kW—allows electric current toflow at full voltage, but only for a portion ofthe time. This causes the lamp to dim just asif less voltage were being delivered (figure11.7).

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Figure 11.7 Solid state dimming control.

Square Law Dimming CurveThe manner in which light output respondsto changes in the control setting is called thedimming curve. If a change in the setting ofthe dimming control, from full bright to fulldim, approximates the change in theamount of electricity allowed to reach thelight source, the dimmer is said to have alinear curve.

The eye is more sensitive to changes inlow intensities of light than to changes inhigh intensities. This relationship betweenlight perceived and light measured is calledthe “square law” curve (figure 11.8).

Electric lamps also respond in a nonlin-ear way: at 81 percent of the voltage, the

light output is 50 percent. If the electricaloutput of a dimmer changes in a linearmanner, then a light source will appear todim faster at low intensities and slower athigh intensities.

To correct this, good-quality dimmersfeature a “square law” dimming curve. Herethe dimmer control moves at constantspeed, but causes the light to dim faster athigh intensities and slower at low intensities.To the eye, the result is a consistent rate ofchange in the light intensity.

Incandescent LampsDimming incandescent sources increasesthe life of the lamp. Yet both incandescent

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Figure 11.8 “Square law” curve: the relationship between perceived illuminance and measured illuminance.

and tungsten-halogen lamps undergo con-siderable shifts toward the orange-red end ofthe spectrum when they are dimmed.Although this increases the warm appear-ance of the lamps at lower light intensities, itis a positive result because people preferwarmer colors of light at lower intensities(figure 11.9).

The efficiency of an incandescent lampis reduced when the source is operated atless than its designed voltage because thetemperature of the filament is reduced. Eventhough the lamps are less efficient at pro-ducing light, much energy is still being saved(figure 11.10).

In some applications, normal operationof dimmers causes lamp filaments to “buzz.”Lower-wattage lamps, physically smaller

lamps, rough service (RS) lamps, low-noisestage lamps, and lamp debuzzing coils helpto decrease this noise.

The lamp debuzzing coil is a separatecomponent. It, too, will hum during opera-tion, so it is remotely located in an areawhere this noise will be acceptable (forexample, a closet or adjacent room).

Low-voltage lampsDimmers for incandescent low-voltageluminaires are installed on the 120 V side ofthe low-voltage transformer. Two kinds oftransformers are manufactured for low-volt-age lighting: magnetic (core-and-coil) andelectronic (solid-state).

Before selecting a dimmer control, it isnecessary to determine which kind of trans-

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Figure 11.9 Dimming incandescent and tungsten-halogen lamps moves light toward the warmer end of the color spectrum.

former is connected to the luminaire. Eachkind of transformer requires a compatibledimmer.

Magnetic-transformer low-voltage dim-mers are used for dimming luminairesequipped with magnetic transformers. Thesedimmers protect the lighting system fromthe dc voltages and current surges to whichmagnetic transformers are sensitive. Mag-netic low-voltage dimmers are speciallydesigned to prevent dc voltage from beingapplied to the transformer and to withstandvoltage “spikes” and current “surges.”

Equipment supplied with electronictransformers requires the use of electronic-transformer low-voltage dimmers. Electroniclow-voltage dimmers are designed specifi-cally for electronic transformers. They elimi-

nate the problems that occur in the interac-tion between the transformer and thedimmer when a magnetic low-voltagedimmer is used with electronic transformers:dimmer buzz, transformer buzz, lamp flicker-ing, and radio frequency interference.

Electronic low-voltage dimmers com-bined with electronic transformers have thevirtue of silent operation, although thesedimmers have a smaller capacity (up to 150W) than magnetic low-voltage ones (up to10,000 W).

Fluorescent LampsDimming fluorescent lamps requires the useof special dimming ballasts, which replacethe standard ballast and must be compatiblewith the dimming control device. Only rapid-

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Figure 11.10 Effect of voltage variation on incandescent efficiency.

start fluorescent lamps can be dimmedbecause voltage is supplied continuously tothe cathodes. When dimmed, the specialballast maintains the cathode voltage sothat the cathodes remain heated to ensureproper lamp operation. Because instant-start and preheat lamp electrodes are turnedoff after the lamps are started, they cannotbe dimmed.

Fluorescent lamps cannot be dimmedall the way to “off.” If they are allowed to dimtoo far, a flicker or spiraling light patternbecomes visible inside the tube.

Many systems dim only 3- and 4-ftlamps. For optimal performance, differentkinds of lamps (T4, T5, T8, or T12) are notmixed on the same circuit. It is also advis-able for all lamps that are controlled by asingle dimmer to be of the same length; dif-ferent lengths dim at different rates.

Dimming fluorescent lamps that operateeither in a cold atmosphere or in an air-han-dling luminaire sometimes results in varia-tions in light output and color, which arecaused by the changes in bulb wall tempera-ture. The color shift is slight; dimmed lampsusually appear cooler in color.

Fluorescent lamp life is reduced by dim-ming systems. Considering that a fluores-cent lamp consumes up to one hundredtimes its cost in energy, a slight loss in lamplife is offset greatly by the savings achievedthrough dimming.

HID LampsIt is technically possible to dim high-intensitydischarge lamps over a wide range of lightoutput, but HID dimming ballasts areuncommon: the long warm-up, restrikedelay, and color shift associated with HIDlamps limit their applications. Multilevel bal-lasts are more frequently used, allowing thelight output to be changed in steps.

A discernible color shift occurs withdimmed HID lamps. In mercury lamps, how-

ever, this slight change will be negligible; thecolor is already inadequate. Clear metalhalide lamps shift rapidly toward a blue-green color similar to that of a mercury lamp.Phosphor-coated metal halide lamps exhibitthe same trend, but less distinctly. HPSlamps slowly shift toward the yellow-orangecolor that is characteristic of LPS lamps.

HID lamps have a shorter life as a resultof dimming. As with fluorescent lamps, theshorter life is offset by energy savingsachieved through dimming.

CENTRAL LIGHTING CONTROLSYSTEMSLocal, single-room systems typically consistof one control station with switches ormanual sliders that control large amounts ofpower. The dimmable wattage is limited onlyby the capacity of the system. These localsystems are easily expanded to multiplerooms and customized to offer many combi-nations of manual, preset, assigned, andtime-clock control. They can incorporateenergy-reduction controls such as occu-pancy sensors and photosensors, and canhandle emergency power functions.

Whole-building systems use local orsmall modular dimmers, a central computer,and master control stations to control all ofthe luminaires in a home or commercialbuilding. Many of these systems also oper-ate other electrical systems, such as motor-ized shades, fans, air-conditioning, heating,and audio systems, and they interface easilywith burglar alarms, “smart” building sys-tems, and other electrical control systems.

In centralized systems, a microproces-sor assimilates the data, determines therequired change, and initiates action tocomplete the change. More sophisticatedprocessors can respond to a number of com-plex lighting conditions in the space, collectpower and energy-use data, and supplysummary reports for building management

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and tenant billing. Processors range in com-plexity from a microchip in a controller to alarge computer.

Three kinds of processors are used:local, central, and distributed. With the localkind, the processor is located in or adjacentto the device it controls; sensor inputs go toa signal conditioner and are then fed to theprocessor. The central processor receives allinputs, analyzes the data, and then sendsinstructions to controllers located through-out a facility, allowing coördinated control ofall system elements. In distributed process-ing, the ongoing decision making is left tolocal processors, but a central processororchestrates the entire system, with theadvantage that the entire system does notfail if any one processor does, and only thelocal processor has to be reprogrammed toaccommodate changes.

Low-Voltage Control SystemsLow-voltage switching and dimming control isachieved with low-voltage wires that operatea relay installed in the luminaire wiring circuit.The relay is either mounted near theluminaire or installed in a remote location.Since the low-voltage wires are small andconsume little electric power, it is possible touse many of them; they can be placed whereneeded without being enclosed in metal con-duit, except where required by local codes.

With low-voltage switching systems, thebranch circuit wiring goes directly to theluminaires; this eliminates costly runs ofconduit to wall switch locations. Whereswitching occurs from three or more loca-tions, the savings are considerable. Manyswitches can control a single luminaire, orone switch (a “master”) can control manycircuits of luminaires.

Power Line Carrier SystemsPower line carrier systems (also called car-rier current systems) are low-cost, simple-

to-install control systems that operate bysending a signal through the building wiring(“power line”). The switch functions as atransmitter that generates the signal. Areceiver located at the luminaire or electricappliance turns a circuit on or off when itsenses the appropriate signal.

As long as the transmitter and thereceiver are connected to the same electricservice in the building, no control wiring isrequired. Any number of luminaires can beattached to one receiver or to any number ofreceivers; any number of transmitters cancontrol any one receiver. Great flexibility isinherent in this kind of system.

Power line carrier systems are subject tomalfunction, however. Automatic garagedoor openers and communication systemsin airplanes flying overhead may operate onthe same frequency as the power line carriersystem, causing luminaires and appliancesto turn on and off when unintended.

Existing wiring systems in older buildingscan significantly reduce the effective rangeof communication between the sensor, pro-cessor, and controller. Additionally, the over-all capacity and speed of this kind of systemis limited.

Energy Management ControlsIn offices of the past, lighting controls wereused to provide lighting flexibility. Today,their major application is energy manage-ment. Simple controls, such as photocells,time clocks, and occupancy sensors willautomatically turn lights on when neededand off when unnecessary. For larger facili-ties, energy management control systemsare designed to integrate the lighting withother building energy systems such as thoseused for heating and cooling.

The key to proper application of thesecontrols is not only the selection of theproper control device, but also the carefulplanning of where and when the control is

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needed. Two basic control strategies areavailable: (1) control in space by electricallypositioning (switching) the light where it isneeded and (2) control in time or supplyinglighting when it is needed.

Daylighting controls have photosensorsthat automatically adjust the electric lightingto preset values. When daylight is availableand suitable (reaching task areas withoutcausing glare, for example), luminaires aredimmed or turned off.

Lumen-maintenance controls compen-sate for the natural deterioration of the light-

ing system and the room surfaces over time.They automatically increase the power to thesystem so that the light output is kept at aconstant value.

It is advisable to use control systems fordaylighting, worker area individualization, andwindow energy management. Individual con-trols in office spaces go a long way towardconserving energy and, equally important,toward giving occupants a sense of controlover their immediate environment.

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LuminairesAlmost all lamps require a method to curtail glare; in addition, many need a

method to modify distribution.

A luminaire provides physical support, elec-trical connection, and light control for anelectric lamp. Ideally, the luminaire directslight to where it is needed while shielding thelamp from the eyes at normal angles of view.

Luminaires are composed of severalparts that provide these different functions:the housing, the light-controlling element,and the glare-controlling element. Dependingon the design requirements and optical con-trol desired, some of these functions may becombined.

HOUSINGSThe electrical connection and physical sup-port for the light source are provided by theluminaire housing. Often its electrical auxiliaryequipment, when required, is also incorpo-rated. Housings are divided into five catego-ries based on how they are supported:recessed, semi-recessed, surface-mounted,pendant-mounted, and track-mounted.

Recessed housings are mounted abovethe finished ceiling, are entirely hidden fromview, and have an aperture (opening) at theceiling plane to allow light to pass through.Some recessed housings are designed to bemounted into the wall, the floor, or the ground.

The electrical connection between thebuilding wiring and the luminaire is made atthe junction box, which is often attached tothe housing (figure 12.1). UL standardsrequire that the connection (“splices”) ofluminaire wires to branch circuit wires beaccessible for field inspection after the light-ing fixture is installed. This access is usuallyaccomplished through the aperture of theluminaire.

Semi-recessed housings are mountedpartially above the ceiling with the remaindervisible from below (figure 12.2). Sometimesthe semi-recessed housing is mounted par-tially in the wall with the remainder project-ing, and in rare cases it is mounted partiallybelow the floor with the remainder visiblefrom above.

Surface-mounted housings are mountedto the surface of a ceiling, a wall, or, in rarecases, a floor. If the ceiling or wall construc-tion permits, the junction box is recessed intothe mounting surface, giving a cleanerappearance (figure 12.3); otherwise, thejunction box is mounted against the surfaceof the ceiling or wall (figure 12.4).

In both cases, the housing serves to par-tially or entirely conceal the junction box.

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12

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Figure 12.1 Recessed incandescent downlight with junction box.

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Figure 12.2 Semi-recessed incandescent downlight with junction box.

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Figure 12.3 Surface-mounted incandescent downlight with recessed junction box.

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Figure 12.4 Surface-mounted incandescent downlight with surface-mounted junction box.

Because the housing of a surface-mountedluminaire is visible, it becomes a design ele-ment in the space.

Pendant-mounted housings also makeuse of a recessed or surface-mounted junc-tion box located at the ceiling for electricalsupply connection, but the luminaire is sep-arated from the ceiling surface by a pendantsuch as a stem, chain, or cord. The junctionbox is concealed by a canopy (figure 12.5).

Pendant-mounted luminaires are usedto provide uplight on the ceiling plane or tobring the light source closer to the task oractivity in the space. At other times pendant-mounted luminaires are selected for decora-tive impact, as with a chandelier.

In high-ceiling spaces, bringing the lightsource down closer to the floor is often unnec-essary. Instead of suspending the lighting ele-ment down into the space, where it becomesvisually dominant, a more concentrated sourceat the ceiling plane is less conspicuous.

With track-mounted luminaires, arecessed, surface-mounted, or pendant-mounted lighting track provides both physi-cal support and electrical connectionthrough an adapter on the luminaire.

The main advantage of track is its flexi-bility. Track is often used where surfaces andobjects to be lighted will be frequently oroccasionally changed, or added or deleted,as in a museum or gallery. It also serves asan inexpensive way to bring electrical powerto where it is needed in renovation andremodeling projects.

LIGHT AND GLARE CONTROLLuminaires can be divided into five categoriesthat describe their lighting function: down-lights, wash lights, object lights, task lights,and multidirectional lights.

DownlightsDownlights, also called direct luminaires,produce a downward light distribution that is

usually symmetrical. They are used in multi-ples to provide ambient light in a large spaceor for providing focal glow on a horizontalsurface such as the floor or workplane(figure 12.6).

Point source downlightsA nondirectional, concentrated light sourceis often mounted in a reflector to control itsdistribution and brightness because thesource would otherwise emit light in all direc-tions. In an open-reflector downlight, areflector made from spun or hydroformedaluminum accomplishes both purposes. A-lamp downlights allow for efficient use ofinexpensive and readily available A-lamps(figure 12.7).

Tungsten-halogen (figure 12.8), com-pact fluorescent (figure 12.9), and HIDopen-reflector downlights (figure 12.10)operate under the same principle as the A-lamp downlight. Fluorescent and HID aper-tures are larger because the source is larger.For a given source, the larger the aperture,the greater is the efficiency of the luminaire.

Economy versions of the open-reflectordownlight, often called “high hats” or“cans,” use an imprecise reflector to directlight downward and either a black multi-groove baffle or a white splay ring for bright-ness control. These luminaires usually pro-vide too much glare for visual comfort andare inefficient at directing light down to hori-zontal surfaces. Although they are lessexpensive initially, they provide only short-term value: more watts are used to achievean equivalent quantity of light.

Ellipsoidal downlights were earlyattempts at controlling the luminance of thesource and providing a wide, soft distribu-tion. They sometimes used silver-bowl lampsand were excellent at reducing the bright-ness of the aperture; they were, however,inefficient at directing light downward. Theseluminaires were large because the elliptical

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Figure 12.5 Pendant-mounted incandescent downlight with recessed junction box covered by a canopy.

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Figure 12.6 Side-mounted, A-lamp, shallow-depth downlight.

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Figure 12.7 Incandescent, parabolic, open-reflector downlight with 5-in aperture.

reflector is larger than the parabolic contour;they are used infrequently today (figure12.11).

Shallow-contour, silver-bowl, open-reflec-tor downlights are used for a general diffusionof light combined with sparkle at the ceilingplane, which is provided by the luminaire’s“pebbled”-surface aluminum reflector. The

reflecting bowl of the lamp throws light up intothe luminaire reflector, which in turn redirectsthe light in a controlled downward beam(figure 12.12). The silver-bowl lamp providesbuilt-in glare control.

Directional-source downlights do notrequire a light-controlling element becausethe AR, MR, PAR, or R lamp provides that

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Figure 12.8 Tungsten-halogen, parabolic, open-reflector downlight with 7-inch aperture.

function. Luminaires for these sourcesrequire only a brightness-controlling ele-ment; the most efficient is the open para-bolic reflector. These luminaires arerelatively easy to maintain: very little dirt col-lects on the underside of the lamp, andevery time the lamp is changed, the entireoptical system is replaced (figure 12.13).

R14 or R20 downlights are sometimesused with spot lamps when a narrow beamof light is desired from a small aperture(figure 12.14), but PAR16 and PAR20lamps are more efficient. R30 and R40downlights are infrequently used; the widespread of the R flood lamp is available froman A-lamp downlight, which is more efficient

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Figure 12.9 Compact fluorescent, parabolic, open-reflector downlight with 6-inch aperture.

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Figure 12.10 Low-wattage, metal halide, parabolic, open-reflector downlight with 7-in aperture.

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Figure 12.11 Incandescent, ellipsoidal, open-reflector downlight with 4½-in aperture.

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Figure 12.12 Incandescent, shallow-contour, silver-bowl, open-reflector downlight with 7¼-in aperture.

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Figure 12.13 Parabolic, open-reflector PAR downlight with 7-in aperture.

and uses a source that costs approximatelyone-fifth as much (figure 12.15).

When a more concentrated beam isdesired, PAR lamps are more efficient, deliv-ering more light at a given wattage for thesame cost. PAR lamp downlights are usedfor greater emphasis on the horizontal planethan is usually produced by other downlights(figure 12.13). This greater intensity of lightis called “punch.”

Almost all open-reflector downlights haveround apertures. Reflectors are available witheither an overlap flange or a flush ceiling

detail. The overlap flange is used in gypsumboard and acoustical tile ceilings to concealthe uneven edge at the ceiling opening. Flushdetails are used in plaster ceilings to create aneat, finished appearance; the ceiling is plas-tered directly to the edge of a plaster ring orframe (figure 12.16).

Reflectors. Specular aluminum reflectorsproduce the most efficient beam control.Semi-specular reflectors are slightly less effi-cient, but they eliminate irregularities in thelamp beam or reflected images of the fila-

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Figure 12.14 Parabolic, open-reflector R20 downlight with 3½-in aperture.

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Figure 12.15 Parabolic, open-reflector R40 downlight with 10-in aperture.

ment coil or lamp phosphors. Although thisslight diffusion of the reflector surface yieldsa reflector of greater luminance than a spec-ular one, the semi-specular reflector stillappears to be of low brightness when viewedin the ceiling plane.

Specular and semi-specular aluminumreflectors should be treated like fine glass-ware. Dirt, fingerprints, and scratches spoilthe appearance and diminish the perfor-mance of reflectors. It is advisable to handlereflectors carefully during construction; once

installed they may be cleaned with a softcloth and glass cleaner or removed andcleaned in a dishwasher or industrial wash-ing machine.

Rectilinear fluorescent downlightsFluorescent downlights are based on thesame principles as the incandescent down-light. They typically use either rapid-start T8,T12, or long compact fluorescent sources.

Common sizes for rapid-start fluores-cent downlights, also called “troffers,” are 1

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Figure 12.16 Parabolic, open-reflector downlight with flush-flange reflector.

ft × 4 ft, 2 ft × 4 ft, and 2 ft × 2 ft; the lastof these is used when a nondirectional(square) ceiling element is desired. Becausethese luminaires take up such a large por-tion of the ceiling surface (as compared to around-aperture downlight), they are signifi-cant factors in the design and appearance ofthe ceiling plane (figure 12.17).

Suspended ceiling systems frequentlyuse 2 ft × 4 ft fluorescent downlightsbecause they integrate easily. Square 1 ft ×1 ft and 1.5 ft × 1.5 ft luminaires with com-

pact fluorescent sources take up a smallerportion of the ceiling surface, providingenergy-effective luminaires in compact sizes.

Shielding. With all fluorescent down-lights, the shielding material is the criticalcomponent, because this element is mostprominent in the direct field of view. The pur-pose of diffusers, lenses, louvers, reflectors,and other shielding materials used in fluores-cent downlight luminaires is to redirect lightfrom the glare zone down toward work surfaces.

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Figure 12.17 Fluorescent 1 ft ×4 ft eight-cell parabolic downlight.

Prismatic lenses incorporate a pattern ofsmall prisms or other refractive elements toreduce the brightness of the luminaire andinhibit direct glare. But almost all fluorescentluminaire lenses fail to reduce their lumi-nance sufficiently to provide visual comfortand prevent bright images in VDT screens.The excessive contrast between the lens andthe ceiling plane also creates distractingreflections.

Egg-crate louvers are made of intersect-ing straight-sided blades that reduce lumi-nance by blocking light rays that otherwisewould emerge at glare angles. They aremade of translucent or opaque plastic orpainted metal. Egg-crate louvers are ineffi-cient in transmitting light, controlling glare,and preventing VDT screen reflections.

Parabolic louvers control luminance pre-cisely; they consist of multiple cells with par-abolic reflectors and a specular or semi-specular finish. The cells range in size from½ in × ½ in to 1 ft × 1 ft.

Small-cell parabolic louvers reduceluminance, but are inefficient in light output.To maximize efficiency, they often have ahighly specular finish, which may cause sucha low luminance at the ceiling plane that theroom seems dim and depressing.

Deep-cell open parabolic louvers offerthe best combination of shielding and effi-ciency.

To avoid reflected glare in VDT screens,IESNA recommends that average luminaireluminance be less than

850 cd/m2 at 55° from nadir350 cd/m2 at 65° from nadir175 cd/m2 at 75° from nadirA manufacturer’s luminaire photometric

report should include a luminance summarythat tabulates brightness values at anglesabove 45° from nadir. This summary may beused to evaluate the suitability of directluminaires in offices with VDTs.

Although use of the footlambert (fL) isdiscouraged, some manufacturers still pro-vide average luminance data in fL instead ofcd/m2. To check compliance with these limits,multiply the fL values by 3.42 to determinecd/m2.

Spacing criterionManufacturers will sometimes publish theluminaire spacing criterion (SC) for theirdownlight equipment. This is an estimatedmaximum ratio of spacing to mounting-height above the workplane in order to pro-duce uniform, horizontal illuminance. SC is alow-precision indicator; its purpose is to aidthe designer in quickly assessing the poten-tial of a downlight luminaire to provide uni-form illumination of the horizontal plane.

SC values are sometimes assigned foruplights, but they are rarely assigned to wall-washers, object lights, task lights, or multidi-rectional lights because these luminaires arenot intended to provide uniform, horizontalilluminance.

Luminous ceilingsA luminous ceiling also provides direct,downward distribution. It consists of a planeof translucent glass or plastic—often thesize of the entire room—suspended below aregular grid of fluorescent lamps. The sus-pended element becomes the finished ceil-ing. This technique, popular in the 1950sand 1960s, provides uniform, diffuse, ambi-ent light (figure 12.18).

The cavity above the luminous planemust be free of obstructions and all sur-faces are to be finished with a high-reflectance (80 to 90 percent), matte-whitepaint. Luminous ceilings share the samedrawback as indirect lighting—they lighteverything from all directions, with no shad-ows or modeling, giving the gloomy effect ofan overcast sky.


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Wash LightsWash lights are luminaires that provide aneven “wash” of relatively uniform brightness,usually on a wall but occasionally on a ceil-ing. In rooms of moderate size, walls areoften the major element in the field of view;washing walls with light has properly becomea major technique in the practice of creativeillumination.

To minimize specular reflections near thetop of lighted vertical surfaces, a matte (dif-fuse) finish is essential. Specular surfaces,such as mirrors and highly polished marble,cannot be lighted because the light receivedon the surface is reflected down to the floorand no impression of brightness is created.

Walls are lighted in two ways: (1) byusing a row of individual, asymmetric-distri-bution luminaires placed parallel to the wallat a distance of about one-third the height ofthe wall, and with the individual units spacedabout the same distance apart from eachother as they are away from the wall; or (2)

by using a system of linear sources or, ide-ally, closely spaced directional sourcesmounted in a continuous “slot” adjacent tothe wall.

Asymmetric wall-washersAsymmetric wall-washers are used for lightingwalls, sometimes to light artwork, and occa-sionally to create ambient light in a space.

All asymmetric wall-washers use reflec-tors or directional lamps or both, frequentlycombined with lenses to spread the lightsideways and smooth the beam. They fallinto two categories: downlight/wall-washersand reflector wall-washers.

Downlight/wall-washers. The combinationdownlight/wall-washer is a special kind ofwall-washer. It consists of a parabolic, open-reflector downlight with an added ellipticalreflector, sometimes called a “kicker” reflec-tor (figure 12.19). This additional reflector“kicks” light up toward the top of the wall,

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Figure 12.18 Typical luminous ceiling.

eliminating the parabolic scallop that is cre-ated by the normal, conical light patternwhen it intersects a wall.

The downlight/wall-washer looks identicalto the same-size aperture open-reflectordownlight. This makes it possible to usedownlights (without kickers) for general roomillumination and to then add downlight/wall-washers adjacent to the walls, usually oncloser centers for uniformity of illumination.

Downlight/wall-wash luminaires areavailable for incandescent A, tungsten-halo-gen, compact fluorescent, mercury vapor,metal halide, and HPS lamps. Variations ofthe downlight/wall-washer have been devel-oped to light adjacent walls forming a corner(downlight/corner wall-washer), to lightopposite sides of a corridor (downlight/double wall-washer), and to light the wallnext to a door without spilling through the

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Figure 12.19 Parabolic, open-reflector downlight/wall-washer with 5-in aperture.

doorway and causing glare (downlight/halfwall-washer) (figure 12.20).

Downlight/wall-wash luminaires havedownlight distributions in three directions vir-tually unchanged by the kicker reflector. Theywork well in small rooms, such as a 10-ft-wide office where opposite walls are lighted;the downlight component provides goodmodeling of faces throughout the room. Thelighted vertical surface is moderately lighted;the horizontal and vertical planes appear tohave relatively equal emphasis.

Reflector wall-washers. A greater empha-sis on the vertical surface is provided byluminaires that light only the walls withoutany significant downward distribution. Reflec-

tor wall-washers make use of sophisticatedoptical systems to provide distribution andluminance control. There are two kinds ofreflector wall-washers: lensed wall-washersand open-reflector wall-washers.

Lensed wall-washers contain a lamp,preferably a directional source; an internalkicker reflector; a spread lens; and a bright-ness-controlling reflector to shield glare (fig-ures 12.21 through 12.24). Lensed wall-washers are available for tungsten-halogenMR and PAR, compact fluorescent, metalhalide, and HPS lamps.

Reflectors that are not circular, para-bolic, elliptical, or hyperbolic are called non-focal reflectors. Open-reflector wall-washershave a compound-contour reflector shape

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Figure 12.20 Typical room layout using matching-aperture, parabolic, open-reflector downlights and downlight/wall-washer variations.

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Figure 12.21 Recessed PAR38 lensed wall-washer.

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Figure 12.22 Surface-mounted PAR38 lensed wall-washer.

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Figure 12.23 Pendant-mounted PAR38 lensed wall-washer.

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Figure 12.24 Track-mounted PAR38 lensed wall-washer.

that combines an ellipse with a parabola (fig-ures 12.25 through 12.27) or they use non-focal shapes. Open-reflector wall-washersrequire a point source with a compact fila-ment; they are available for tungsten-halogenT3 and T4 and ceramic metal halide T6 lamps.

Lensed and open-reflector wall-washersused without downlights provide a shadow-less, low-contrast setting. When people aredistant from the lighted wall they are seen asflat-featured; people next to the lighted wallare seen as silhouettes. These problems areavoided by adding downlights.

Wall-washing is also produced by dif-fuse-source, fluorescent-lamp wall-washsystems. The inability of a diffuse source toproject a high intensity toward the bottom ofa wall usually results in a bright area at thetop of the wall and a rapid falloff of lumi-nance thereafter. Sophisticated reflectorsystems with a wide aperture help to solvethis problem (figure 12.28). Fluorescentwall-wash systems, sometimes called “per-imeter” wall-wash systems, are moreenergy-effective than their incandescentcounterparts.

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Figure 12.25 Recessed tungsten-halogen T4 wall-washer.

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Figure 12.26 Surface-mounted tungsten-halogen T4 wall-washer.

Figure 12.27 Track-mounted tungsten-halogen T4 wall-washer.

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Figure 12.28 Fluorescent reflector wall-wash luminaire.

Linear wall-washersContinuous slots are located in the ceilingnext to the wall and can enclose other kindsof wall-wash luminaires (figure 12.29). Theceiling is de-emphasized, while vertical sur-faces such as walls, murals, and draperiesare given prominence.

Incandescent systems. Wall-washing mayalso be provided by individual directionallamps mounted on a repetitive spacing in acontinuous, linear raceway. These systemsrequire the use of a directional point sourcethat is able to project its light over the heightof the wall (figures 12.30 and 12.31). Themultiple beams of the repetitive lamps over-lap, producing uniform brightness along thebreadth of the wall.

Lamps are typically mounted close to thesurface being lighted. The distance from thelamps to the wall and the distance betweenthe lamps are determined by a full-size mock-up. Excessive lamp spacing will cause scal-lops. To minimize scallops, the following max-imum lamp spacing serves as a guide:

For PAR flood lamps:maximum spacing is 0.8 × thedistance to the wall

For R flood lamps:maximum spacing is 1.0 × thedistance to the wall

Fluorescent lamps. The minimum discern-ible variation in luminance is approximately2:1. Even with the aid of precisely formed

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Figure 12.29 T8 fluorescent wall-washer with compound-contour reflector in continuous slot.

compound-contour reflectors, fluorescentlamps have difficulty projecting a high inten-sity toward the bottom of a wall. The follow-ing guide will be helpful in providingapproximate visual uniformity with linear T5,T8, and T12 fluorescent lamps.

When using fluorescent lamps in stan-dard reflector channels to light walls, displayboards, or draperies, place the channels at a1:4 ratio of distance away from the lightedsurface to the height of the wall (figure12.32). Luminance at the bottom will beabout one-tenth of the luminance at the top.For many applications, the resulting percep-tion of near uniformity is adequate.

Luminaires placed closer than the 1:4ratio, called grazing light, emphasize surfacetexture and low sculptural relief. But thismay also increase the awareness of irregu-larities and lack of flatness of the lighted sur-face. Additional frontal light, direct orindirect, reduces this problem by filling in theminute shadows cast by the irregularities.

When lighting from two opposite sides,or from four sides, place the channels at a1:6 ratio of distance away from the lightedsurface to the height of the wall. The 1:4 and1:6 placement ratios are also applicablewhen fluorescent channels are mounted ver-tically (figure 12.33).

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Figure 12.30 Typical incandescent raceway wall-washer system.

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Figure 12.31 Manufactured linear wall-washer system includes linear spread lenses to distribute light evenly across thewall and baffles to shield the view of the lamps along the length of the slot.

Vertically mounted fluorescent channelsare used for wash light when the ceilingheight is low and the placement of overheadequipment is difficult (figure 12.33), butgreat care must be taken to avoid glare. Theshielding angle for blocking the view of thevertical light source is even more critical thanit is for horizontal slots and valances.

The close placement of the light sourceto the wall makes the luminance on the wallmuch higher near the source. Fluorescentcontinuous slots and vertically mountedchannels are useful techniques when thisnonuniformity of luminance is acceptable.

Lighting the ceiling plane“Washing” with light has come to mean theuse of a continuous row of lighting deviceslocated at the edge of the “washed” surface.Ceilings are usually not “washed”; they arelighted by devices known as uplights or indi-rect luminaires (figure 12.34). These are

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Figure 12.32 Uniformity is slightly improved when thefloor has a high reflectance or has a high-reflectanceborder at the wall.

Figure 12.33 Illumination from two opposite sides withvertically mounted fluorescent channels. When fluores-cent lamps are used, the cross-section dimension ofthe luminaire can be made smaller by locating the bal-lasts remotely.

suspended from the ceiling by stems orcables; mounted on top of furniture aboveeye level; or attached to walls, columns, orthe tops of floor stands. Some provide indi-rect light only; others, usually stem-mounted,also have a downlight component.

Uplights. Point-source indirect luminairesoften use linear sources, such as T2½, T3,and T4 tungsten-halogen lamps; ED18, T6,T7, and T15 metal halide lamps; and ED18and T15 HPS lamps. Diffuse-source indirectluminaires use compact, T5, T8, and T12fluorescent lamps.

Fluorescent uplights (figure 12.35) weredeveloped primarily to provide an evenly illu-minated ceiling similar to the recessed lumi-nous ceiling (figure 12.18). The intent is thesame: to create an evenly illuminated ceilingplane without variations in luminance on theceiling surface.

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Figure 12.34 Typical tungsten-halogen uplight.

Figure 12.35 Typical fluorescent uplight (“indirect”)luminaire.

Uplights are especially suitable for high-ceilinged rooms, which permit the luminairesto be positioned far enough below the ceilingto avoid “hot spots.” If they are mounted tooclose to the ceiling surface, the variations inlight and dark will often be unpleasant anddisturbing; the ceiling surface will become aseries of hot spots and dark shadowsinstead of an evenly illuminated plane.

Researchers have demonstrated thatpeople perceive a greater quantity of light ina given area when they can see the source ofillumination. Pendant-mounted fluorescentuprights that provide a source of brightnessfrom below give an impression of increasedilluminance. Uplights that are completelyopaque (dark) from below yield an impres-sion of lower illuminance.

Furniture-mounted uplight luminairesincorporate an indirect lighting element onto

the top of furniture or freestanding partitions(figure 12.36). They are usually mountedwith their apertures slightly above averageeye height at 5 ft 6 in AFF in order to avoidglare. Furniture and partition layouts mustaccommodate the luminaire’s spacing crite-rion to achieve uniform ceiling luminance.

Wall- or ceiling-mounted uplight lumi-naires are mounted to walls and columns(figure 12.37). Like wall-washers, they havean asymmetric light distribution that pro-duces a sweep of light across the ceiling andavoids hot spots and “spill light” on adjacentsurfaces.

Architectural coves. Coves are anothermethod of providing general ambient light inhigh-ceilinged rooms (figure 12.38). Theirluminaires direct light toward the ceilingplane, which—like a washed wall—becomes


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Figure 12.36 Furniture-mounted indirect luminaire.

a large-area diffusing source. Coves areuseful to supplement more energy-effectivelighting methods, such as recessed down-lighting systems.

The placement ratios in figure 12.38 areintended to produce approximate visual uni-formity. Specular reflections are minimized ifthe ceiling surface is a high-reflectancematte or satin finish. Typical cove dimen-sions are shown in figure 12.39.

Custom-built coves are constructed ofwood, plastic, or metal. A glass or plasticbottom is sometimes used to introduce adownward component of light for sparkle.

Fluorescent lamps or cold-cathodetubes are commonly used in coves becausethey are energy-efficient, linear sources. All

lamps must be of the same color, and it isbest that they are of the same tube diameterand have the same manufacturer to preventcolor variations on the lighted surfaces.Lamps of similar light output per foot oflength are also desirable to avoid noticeablevariations in luminance on the illuminatedsurfaces.

When the lamp mounting channels areplaced end-to-end, a noticeable gap in lightoccurs because the lampholders take upspace and the lamps emit less light neartheir ends. The shadows caused by this gapmay be avoided by staggering the mountingchannels so that they overlap by at leastthree inches. Prefabricated single-lamp andtwo-lamp staggered channels with overlap-

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Figure 12.37 Column-mounted indirect luminaire.

ping lamps achieve the same result (figure12.40).

When space constraints limit the covedesign so that the source is located tooclose to the adjacent wall and ceiling, thesesurfaces will appear excessively bright.Shields can be incorporated into the covedesign to intercept some of the light and pre-vent it from reaching the upper wall. Theupper wall will be lighted by reflection fromthe cove lip and ceiling, reducing the lightgradients (figure 12.41).

To ensure uniformity on the ceiling plane,the distance from the center line of the lampto the ceiling must be a minimum of 12 in forrapid-start lamps and 18 in for HO and VHOlamps. Curved transitions between adjacentsurfaces will produce more gradual, softergradients (figure 12.42).

The height of the vertical shield or “lip”of the cove is determined by a sight lineanalysis. On a section drawing through thecove, draw a line between a viewer’s eye,located at the farthest viewing point, and theedge of the cove lip (figure 12.43). The lip ofthe cove is designed to shield the lamp atnormal viewing angles but must not interfere

with the distribution of light across the ceil-ing (figures 12.44).

When incandescent directional sourcesare used in a linear array, the beam axis isaimed at a point two-thirds of the way acrossthe lighted surface. This provides relativeuniformity of illumination (figure 12.45).

Object LightsAdjustable object lights, sometimes impre-cisely called “accent lights,” provide a sym-metric distribution of light aimed at one orseveral objects. They use a directional sourcesuch as an AR, MR, PAR, or R lamp. Alsocalled “spot lights,” they are used to providefocal glow and add contrast to a setting.

Recessed, adjustable, object lights mayhave a horizontal rotation stop to preventwires from tangling as the lamp is rotated.Vertical adjustment is from 0° to between35° and 45° (figure 12.46). Surface-, pen-dant-, and track-mounted luminaires have agreater range of vertical adjustment thanrecessed equipment (figures 12.47 and12.48). The best track-mounted adjustableobject lights are designed to rotate slightlymore than 360°; inferior luminaires have a

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Figure 12.38 A 1:4 placement ratio is applicable when light is emitted from one side only. A 1:6 ratio isapplicable when light is emitted from two or four sides.

Figure 12.39 Typical cove dimensions for two-lamp fluorescent cove.

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Figure 12.40 Single-lamp fluorescent staggered channel.

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Figure 12.41 External shield to prevent light from reaching the upper wall.

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Figure 12.42 Curved contour for architectural cove.

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Figure 12.43 Shielding angle for coves.

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Figure 12.44 Typical cove “lip.”

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Figure 12.45 Typical incandescent lamp raceway in an architectural cove.

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Figure 12.46 Recessed, incandescent, adjustable-angle object light.

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Figure 12.47 Surface-mounted, incandescent, adjustable-angle object light.

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Figure 12.48 Track-mounted, incandescent, adjustable-angle object light.

“blind spot” with horizontal rotation limitedto between 300° and 350°.

Whether surface-, pendant-, track-mounted, or recessed, adjustable objectlight housings are usually designed to shielddirect view of the lamp while avoiding undueinterference with the beam pattern of direc-tional lamp sources.

The least expensive luminaires may lackany brightness control, and the source glarecan be uncomfortable. Better-quality lightingfixtures provide greater degrees of bright-ness control, typically using an open reflec-tor in recessed equipment and cube-celllouvers or baffles in surface-, pendant-, andtrack-mounted luminaires.

Louvers intercept some of the light inthe beam. Cube-cell louvers reduce lightoutput as much as 50 percent. Cross-bafflesare a more efficient method of shielding lampsfrom the eyes because the light loss is mini-mized.

When used to illuminate artwork andlarger objects, object lights are also suppliedwith a linear spread lens to modify the distri-bution and soften the edge of the beam.Linear spread lenses are typically made ofborosilicate glass with a fluted pattern; theyare usually designed to spread the beam inone direction only and are rotated asrequired during luminaire focusing. Withoutthe spread lens, the same object lightsource provides a symmetrical, concen-trated beam-spread suited to smallerobjects and those that require a greaterintensity of illumination or “punch.”

Object lights contribute to a moderate-to high-contrast setting because they intro-duce nonuniform illumination. Medium- towide-beam lamps give moderate contrast;narrow-beam lamps give high contrast.

Task LightsTask luminaires bring the light source closeto the surface being lighted. They are useful

for work surfaces of systems furniture, whichmay receive insufficient light from an over-head lighting system because of shadowsfrom vertical partitions and furniture-mounted high shelves and cabinets.

Local task luminaires are often energy-effective and useful for reducing reflectionsin VDTs. Task lighting uses less powerbecause the source is closer to the surfacebeing lighted. Task luminaires can providethe illuminance required for paper-basedvisual tasks while allowing the ambient lightto be of a lower illuminance and decreasingthe chances of distracting VDT screen reflec-tions.

Task luminaires are often mounted undera cabinet or shelf that is directly over the workstation (figure 12.49). This location is in thereflected glare zone, however; the luminairemay produce veiling reflections on the worksurface. This is eliminated by using opticallenses for the luminaire that block the per-pendicular light rays and convert them to raysthat fall on the task from the side and thus donot cause veiling reflections.

Adjustable task luminaires are usuallymounted at one side of the task. An adjust-able arm permits positioning the luminaire tosuit the task, maximizing task visibility. Anasymmetric light distribution is sometimesincorporated to direct light more uniformlyover the task area.

SoffitsA lighting soffit is used for task light (focalglow) rather than ambient light. It is locatedadjacent to a wall or similar vertical surfaceand is sometimes used to light niches. Thetop is often closed and all light is directeddownward (figure 12.50).

Over work areas, reflectors increase theuseful light (figure 12.51); open louvers orlightly etched plastic or glass perform best.Matte finishes for work surfaces minimizespecular reflections (figure 12.52).

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For make-up and grooming areas, atranslucent diffusing panel lights faces frommany directions, minimizing harsh shadows.A light-colored countertop is of further help,as it reflects light back toward the face(figure 12.53).

Low brackets. Low brackets are used forlighting special task areas such ascountertops and writing or reading surfaces(figure 12.54).

Multidirectional Luminaires

Direct-indirect luminairesDirect-indirect luminaires provide a combi-nation of downlight (direct lighting) and

uplight (indirect lighting), with all of theattributes of both systems. The sharpershadows created by direct systems are soft-ened by the diffuse, indirect light. Theincreased ceiling luminance creates agreater diffusion of light in the space.Interreflections reduce ceiling plane lumi-nance variations and the resulting VDTscreen reflections.

Valances. A lighting valance is used overwindows, usually combined with draperies,or special features, such as artwork. It pro-vides both indirect uplight that reflects backfrom the ceiling for ambient illumination anddownward wash-light for the drapery or art-work (figure 12.55).


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Figure 12.49 Sometimes under-cabinet or under-shelf task luminaires cause veilingreflections. This is eliminated by using a luminaire equipped with a lateral lens.

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Figure 12.50 Typical lighting soffit. Electronic ballasts will eliminate noise.

Figure 12.51 Typical lighting soffit over work area with fluorescent reflector channel.

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Figure 12.53 Typical lighting soffit for make-upand grooming areas.

Figure 12.52 Typical lighting soffit over work areawith open louver.

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Figure 12.54 Lighted low bracket.

High brackets. High brackets are usedon interior windowless walls. They provideboth uplight and downlight for ambientilluminance or specific emphasis on surfacesand artwork (figure 12.56).

Decorative LuminairesDecorative luminaires are used to provideambient lighting in areas where their appear-ance contributes to the design harmony ofthe space (figure 12.57). They are available

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Figure 12.55 Lighted valance.

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Figure 12.56 Lighted high bracket.

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Figure 12.57 Decorative luminaires provide ambient light while contributing to the design harmony of the space.

as ceiling-mounted globes and diffusers(figure 12.58), pendant-mounted and sus-pended chandeliers (figure 12.59), wall-mounted lanterns and sconces (figure12.60), floor- and ceiling-mounted cornerlights, and floor-mounted torchères (figure12.61).

Almost all decorative luminaires pro-duce multidirectional distribution. Somehave optical control hidden inside their dec-orative exteriors to provide a specific distri-bution of light.

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Figure 12.58 Ceiling-mounted diffuser luminaires.

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Figure 12.59 Pendant-mounted luminaires

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Figure 12.60 Wall-mounted sconces.

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Figure 12.61 Floor-mounted torchère.

DesignLighting design is a process. Specifically, it is the process of integrating light

into the fabric of architecture.

Successful lighting is integrated into boththe architectural concept and the physicalstructure.

The lighting concept is integrated intothe architectural concept in three ways: (1)by enhancing the original designer’s concep-tion of the space, (2) by reinforcing the activ-ity in the space, and (3) by highlighting areasto be prominent, while de-emphasizingareas to be subdued.

Lighting equipment is integrated into thephysical structure of the building in threeways: (1) by selecting visible elements thatharmonize with the design motif, (2) byincorporating hidden elements within thearchitectural forms and surfaces, and (3) bycoördinating electrical systems with theother mechanical systems of the building.

VISUAL CLARITYPeople search for simplification of theirvisual fields when faced with demandingtasks and activities. In an environment thatis used for complex activities, too manyvisual stimuli or too many patterns will resultin an overload condition. We become tenseand frustrated and have a diminished abilityto perform a complex task.

When we are reading with music playingnearby, the sound competes with the writtenmaterial yet allows comprehension of sim-pler passages. At a complex portion of thematerial, where the reading task becomesmore absorbing, we instinctively turn thevolume down or off. In doing so, the amountof information that is competing for attentionis reduced.

Meaningless or confusing luminances ina space are similarly distracting. The brainbecomes overstimulated, spending additionaltime and energy sorting out conflicting infor-mation. This is called visual clutter; it is analo-gous to noise or static in acoustical design.

As the activity or task becomes morecomplex (more loaded), visual clutterbecomes more distracting. It affects workerperformance, particularly when the worker isfaced with demanding (more stimulating)tasks. Visual clutter undermines long-termperformance of all complex tasks.

Visual clarity reduces the number ofstimuli in the field of view. It allows us to movethrough space and complete tasks withoutany attention being drawn to the lightingsystem. This leaves our concentration avail-able for the task at hand (figure 13.1).

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It is the designer’s role to simplify thevisual process and the environmental back-ground so that distortions and irrelevantclutter are minimized. The goal is to reducedistractions so that the environment assistsconcentration and conserves our energy forthe demands of more productive tasks andactivities.

Luminaire PatternsAn irregular luminaire pattern on the ceilingconfuses orientation and spatial under-standing. We react negatively not becausetasks are poorly illuminated or because glareproduces discomfort, but because of the dis-tractions produced by the luminaire place-

ment. When the irregular luminaire patterndirects attention to the ceiling, we mustovercome the distraction and consciouslyfocus attention on the activities and moremeaningful visual stimuli in the room.

An organized pattern on the ceiling mini-mizes the effort required to discover orimpose regularity on the environment (figure13.2). Carefully organized brightness patternsand repetitive luminaire layouts are usefultechniques for simplifying the processes of ori-entation and activity comprehension. In addi-tion to establishing organized luminairepatterns, matching luminaire apertures of thesame dimension and finish further reduceconfusion (figure 13.3). Because greater cer-

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Figure 13.1 Low-brightness louvers minimize clutter on the ceiling and establish the primary focus in the activity portionsof the visual field.

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Figure 13.3 Matching luminaire apertures of the same dimension and finish.

Figure 13.2 An organized ceiling pattern simpli-fies orientation and activity comprehension.

tainty is felt in an organized environment, lessattention is paid to it.

Lighting designers are ceiling designers.Lighting layout drawings include locations ofluminaires, sprinkler heads, air diffusers,return grilles, smoke detectors, loudspeak-ers, and so forth. To prevent visual clutter,these ceiling elements are organized in aninvisible grid (figure 13.4).

Whether providing uniform or nonuniformlighting, organize luminaires in a patternbased upon an invisible grid that is related tothe architecture. For example, figure 13.5shows a 78-ft-long room and luminaires witha maximum spacing of 10 ft. The solutionpresented is eight equal spaces measured tothe center line of each luminaire. A half-space at either end ensures adequateilluminance near the walls. In the other direc-tion, which is 36 ft, four equal spaces to thecenter line of each luminaire are shown.

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Figure 13.4 Invisible grid for luminaire placement.

Figure 13.5 1 ft × 4 ft luminairepattern.

It is unnecessary to fill each cross-pointof the invisible grid to maintain the ordersupplied by that pattern. With the round-aperture luminaires in figure 13.6, spacingat the perimeter is half the spacing of the roomto provide uniform wall lighting with open-reflector downlight/wall-wash luminaires.

ARCHITECTURAL SURFACESWhen the primary emphasis of lighted spaceis within the visual field, the resulting pat-terns of brightness reinforce our priorities fordefining space (orientation) and definingactivities (participation).

People define their environment througha process of additive perception. Informationis gathered by scanning the boundaries of a

space, thereby forming a concept of direc-tion and limits. When the lighting system isdesigned to establish the physical bound-aries of a space, it helps people to maintaina sense of direction and an understanding ofspatial form with minimal distraction fromthe environment.

Lighting helps to define and separatethe major surfaces of a space if the shape ofthe light distribution relates to the form ofthe surface. For example, a wall or ceilinglighted with a uniform wash of light willapproximate the form and dimension of thatsurface.

A linear wash of light facilitates clearvisual separation between the vertical andhorizontal planes (the wall and ceiling sur-

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Figure 13.6 6-inch-diameter round-aperture luminaire pattern.

faces and the wall and floor), the borders ofinterior space (figure 13.7). The evenlylighted wall is perceived as an integratedvisual form (figure 13.8). The same is true ofthe evenly lighted ceiling plane.

Lighting Vertical SurfacesVertical surfaces require special attention:they are the first surfaces that we see uponentering a space. Vertical surfaces definethe boundaries of the space; they are usedfor displaying works of art and communicat-ing a message. Clear perception of verticalsurfaces significantly impacts our perceptionof the overall design.

Reliance upon formulas to provide a spe-cific illuminance value on the horizontal planedisregards the importance of vertical sur-faces. Consequently, luminaires used forambient illumination often cast unanticipated

or undesired light patterns on the vertical sur-faces, or leave them in relative darkness. Ifnot distracting, the resulting environment isunintentionally dull and monotonous.

It is critical to anticipate wheredownlight distributions will intersect verticalsurfaces. Scallop patterns and similar irregu-larities are to be minimized. Except for spe-cial situations, a lighted surface is notintended to be perceived as a form or sur-face that is intersected by arbitrary patternsof light; it is intended to be perceived as aunified form.

Scallops of light are incompatible withthe plane form of the wall. Because the eyeis involuntarily attracted to areas that con-trast with the ambient brightness, scallopsresult in a disorienting pattern of superim-posed light that confuses perception of thevisual form of the wall (figure 13.9).

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Figure 13.7 A linear wash of light facilitates spatial clarity.

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Figure 13.8 An evenly lighted wall is perceived as an integrated visual form.

Figure 13.9 Scallops distort the plane form of the wall.

To alleviate scallops when using open-reflector point-source downlights, use down-light/wall-wash reflectors at the perimeter,as indicated in figure 12.20, if the wall sur-face is matte. If the wall surface is specular,no adjustment is necessary; the intersectinglight pattern is unnoticeable on a mirror-likesurface.

Rectilinear fluorescent downlights withsharp luminance cutoff show an abrupt fall-off of light at the upper part of adjacentwalls. This results in a shadow line along thetop of the wall, which often causes a spaceto be perceived as dimly lighted (figure13.10). Wall-washers or a continuous perim-eter system will fill in this shadow. A similarresult is achieved by using a specular wallfinish in the shadow area with a matte finishbelow it.

Irregular patterns of light are sometimesdesirable. A shaft of sunlight has intrinsicvalue, as do some electric light patterns thatavoid a relationship to the physical form of aspace. The value of these irregular patternsof light is that they serve as a temporaryvisual stimulant.

Irregular light patterns are also success-ful when they relate to an appealing attributeof the physical space, such as a painting,sculpture, plant, or architectural detail.Unless specifically intended, however, avoidirregular light patterns.

Matte vertical surfacesThree kinds of lighting systems are availablefor uniform vertical surface illumination ofmatte surfaces: (1) individual unit, point-source wall-wash; (2) continuous, linear,point-source wall-wash; and (3) continuous,linear, diffuse-source wall-wash.

Individual unit, point-source wall-wash. To provide uniform illumination fromtop to bottom, luminaires are placed parallelto the wall at a distance of about one-thirdthe height of the wall. For uniform lightingfrom side to side, the “square rule” applies:luminaires are located on centers closerthan or equal to their distance from the wall.The center-to-center spacing varies with theceiling height and the light intensity desiredon the surface.

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Figure 13.10 Sharp-cutoff luminaires produce shadows along the top of an adjacent wall.

Continuous, linear, point-sourcewall-wash. Uniform lighting is also providedby a grazing light from luminaires locatedclose to the surface being illuminated (figure13.11). The same square rule applies: thelamps are spaced on centers closer than orequal to their distance from the wall. Again,the center-to-center spacing varies with theceiling height and the light intensity desired

on the wall surface. The goal is also thesame: to provide the perception of uniformbrightness both horizontally across the walland vertically from top to bottom.

A full-scale mock-up tests for the follow-ing:

1. Beam-spread overlap (spot beam-spreads usually require a spread lens).

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Figure 13.11 Continu-ous, linear, point-sourcewall wash.

2. The optimum distance away from the walland on-center spacing.

3. The mounting cavity height, depth, andfinishes required.

4. The necessity of baffles to shield thelamps from view along the length of thecavity.

A full-size mock-up is the only way toensure that the finished installation willachieve the desired illuminance value andavoid scallops and striations at the top of thewall. No miniature light sources exist to testthe performance of architectural lamps in ascale model.

Continuous, linear, diffuse-sourcewall-wash. The diffuse fluorescent source isgood at providing even lighting across the wallin the horizontal direction but is inadequate atproviding even illuminance vertically from topto bottom. Reflectors help to mitigate theproblem but fail to solve it for walls exceeding10 ft in height. The use of a fluorescent wall-wash system is reserved for low ceiling areaswith wall heights from 8 to 10 ft.

Specular vertical surfacesWhen providing light for glossy surfaces,such as glass, marble, high-gloss enamels,and varnishes, specular reflections compli-cate the placement of lighting equipment.Careful location and shielding of the sourceprevents distracting reflections and veilingimages.

Think of the glossy surface as a mirror;eliminate glare by minimizing high luminancein the reflected field of view. To reducereflected images, remove bright elements inthe reflected field of view or shield them withproperly located baffles or screens.

People, objects, and other surfaces inthe room become secondary light sources. Ifthey are located in the reflected field of view,

they will cause distracting or veiling reflec-tions in glossy surfaces. In some cases, theperception of varnished or glass-coveredpaintings, or of marble and other specularmaterials, is partially or completely obscuredby such reflected images.

TASK LIGHTINGLighting systems in the workplace provide foraccurate perception at a specific task area(a desk, counter, machine, or workbench).This is achieved by using one of two lightingmethods: a general-ambient approach or atask-ambient approach.

General-ambient systems provide a uni-form quantity of light throughout a space.This approach is often used when the tasklocation is apt to vary widely or when thespace will be reconfigured frequently.

Task-ambient systems are more energy-effective. Higher values of task illuminanceare provided for the workplane while lowervalues of ambient illuminance are providedfor surrounding areas.

Task-ambient systems are appropriatein rooms where task areas are permanentlylocated, such as private offices, factories,laboratories, and stores. Task lighting is pro-vided for task areas, with the remainingspace lighted for more casual activities(figure 13.12).

When designing a task-ambient system,first light the task (focal glow), then supple-ment the task lighting with ambient roomlighting. In typical task-ambient systems,task-oriented luminaires are mounted on ornear the furniture and supplemented by anambient (uniform) lighting system that pro-vides lower illuminance.

Ambient lighting provides overall illumi-nation for circulation, provides balancebetween the VDT task luminance and its sur-round, and provides part of the illuminancefor paper-based tasks. Areas surroundingvisual tasks need less illuminance than the

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visual tasks. For comfort and ease of adap-tation, make the ambient illuminance atleast 33 percent of the task illuminance.

VDTsVDT screens present a particular challengefor designers. Almost all VDT screens have adark, glossy, or satin surface that reflectsimages of the surrounding space; the opera-tor will see luminaires, ceilings, walls, or win-dows as elements of excessive brightnessreflected in the screen (figure 13.13). Thedesigner must carefully select and locateluminaires to minimize reflected images.

VDT tasks often require an almost hori-zontal line of sight when viewing the screen.Because of this, a large area of the ceilingwill be in the field of view in large openoffices. It is critical to minimize variation inluminance on the ceiling plane in order toprevent discomfort glare (figure 13.14).

With well-designed direct luminaires,the luminance of the aperture will be equiva-lent to the luminance of the ceiling. Thisresults in minimal brightness contrast

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Figure 13.12 Task-ambient (nonuniform) office light-ing layout.

Figure 13.13 Normal range for reflected line-of-sight angles in a VDT (65° to 110° from vertical).

between the reflected screen images of theluminaire and ceiling.

With a well-designed indirect system,the light received on the ceiling plane exhib-its an even luminance, yielding minimalbrightness contrast in the VDT screen. Theunderside of the indirect luminaires must beapproximately the same luminance as theceiling plane. When the luminance seenacross the VDT screen is uniform, minimalinterference occurs.

Paper-based tasksAlmost all office work involves paper-basedtasks. Paper documents are referenced forword processing, order entry, informationretrieval, and computer-aided design. Inaddition to the lighting requirements for VDTtasks, lighting for paper-based visual tasksmust also be considered.

AMBIENT LIGHTINGAmbient lighting is provided by two basicmethods: (1) downlighting (direct), whereoverhead luminaires provide a downward

light distribution, and (2) uplighting (indi-rect), where pendant luminaires provideupward light that is then reflected from theceiling.

Downlighting (Direct)With downlighting (direct lighting), luminairesare arranged according to the ambient light-ing requirements for either uniform or nonuni-form distribution over the horizontal work-plane.

For direct ambient lighting, the spacingcriterion (SC), or spacing-to-mounting-height(S/MH) ratio, provided by the luminaire man-ufacturer, gives the maximum recommendedspacing between luminaires to achieve uni-form, ambient lighting.

To quickly assess the potential of adownlight luminaire to provide uniform illumi-nation of the horizontal plane, SC is thecenter-to-center distance between luminaires(spacing) based on their mounting heightabove the workplane.

S = MH × SC

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Figure 13.14 A large area of the ceiling is within the field of view when viewing a VDT.

For example, if the SC = 1.5, then for an8-ft ceiling height,

MH = 8 ft 0 in – 2 ft 6 in to the workplane= 5 ft 6 in AFF

S = 5.5 ft × 1.5 = 8.25 ft

The center-to-center maximum spacing fromthe center of one luminaire to the center ofthe next is thus 8.25 ft (figure 13.15).

For rectilinear luminaires, SC is expressedas parallel or perpendicular, indicating thespacing-to-mounting-height ratio in either thedirection parallel to or perpendicular to theorientation of the lamps within the luminaire.

To maintain uniformity of light intensityover a large work area, avoid exceeding themanufacturer’s recommended maximumSC. Because of wall surface absorption,maximum distance from the last row ofluminaires to the wall is usually one-half toone-third the spacing in the room to preventa falloff in illuminance near the walls (figures13.16 to 13.18).

Even with this reduced spacing, worksurface illuminance near the walls is oftenonly half that measured in the center of theroom. In critical seeing areas, supplemen-tary luminaires are added near the wall(figure 13.19).

Office partitions block some overheadlight from a direct system, preventing it fromreaching work surfaces. Depending on thelocation of the downlights, some areas willbe left in shadow (figure 13.20). Well-designed uplighting, because it produceseven illuminance overhead, softens andreduces this shadowing.

Uplighting (Indirect)The primary use of uplighting (indirect light-ing) is to create evenly luminous ceilings thatreduce VDT screen reflections. For uplightingto be successful, luminance differences onthe ceiling plane must be minimal. If brightpatches of higher luminance occur, they arereflected in the VDT screen, causing a dis-tracting background.

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Figure 13.15 Spacing-to-mounting-height ratio.

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Figure 13.16 Linear pattern, continuous 1 ft × 4 ft rec-tilinear luminaires.

Figure 13.17 Regular pattern, 2 ft × 2 ft squareluminaires.

Figure 13.18 Regular pattern, 6-inch-diameter round-aperture luminaires.

Figure 13.19 Supplementary illumination near thewall.

Uplighting systems also increase the ver-tical illumination in a space. While this isdesirable for many surfaces, it reduces imagecontrast on VDT screens. Although indirectlighting systems eliminate the most offensiveimage glare common with direct lighting onVDTs, they may introduce less-problematicveiling reflection and contrast reductions onthe surface of the screen.

A well-designed indirect luminaire has awide distribution. Multiple luminaires arelocated so that their light output will beevenly distributed across the ceiling withouthot spots or areas of high luminance (fig-ure 13.21). The goal is uniform ceilingbrightness, where luminances and lumi-nance ratios are consistent throughout thespace.

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Figure 13.20 Some areas have noticeable shadows from office partitions,especially when partitions are located on three sides of the work surface.

Figure 13.21 Above, properly located indirect luminaires with wide distributions produce even luminance; below, improp-erly located indirect luminaires with narrow distributions produce areas of uneven luminance.

To avoid distracting brightness variationin VDT screens, keep the variation in ceilingluminance to a ratio of less than 4 : 1. Inaddition, limit the average luminance of any2 ft × 2 ft area of the ceiling to less than850 cd/m2, measured at any angle. Applythis same limit to windows, walls, and parti-tions that will be reflected in the VDT screen.

The diffuse light from indirect systems,however, reduces our sense of visual clarity,depth perception, and sense of orientation.This lack of highlight and shadow is miti-gated by a greater use of surface color, walllighting, or object lighting; these techniquesadd visual interest, thus enhancing percep-tion of the environment.

Some indirect luminaires incorporate aluminous element that is visible from below.This is psychologically beneficial becausepeople feel more comfortable when they canidentify the source of light. This visible lumi-nous element also increases the perceptionof brightness in a space and introducesvisual highlight into a shadowless environ-ment.

In a small office, only part of the ceilingwill be reflected in the VDT screen. Here, it isthe walls that are of concern. The walls of asmall office must have sufficient luminanceto avoid noticeable contrast between thesewalls and the ceiling, a condition that causesdistracting contrast in VDT screens.

Downlighting Versus UplightingThe appearance of a low-brightness directlighting system differs considerably from anindirect lighting system. The direct systemproduces negligible luminance on the ceilingplane and provides great emphasis on thehorizontal work surface, furniture, and floorcoverings. The indirect system places lumi-nance emphasis on the ceiling plane and de-emphasizes the surfaces in the lower half ofthe room. A direct-indirect system accom-plishes both.

LIGHTING ART

Lighting Three-Dimensional ObjectsThree-dimensional objects are perceived asa result of the relationship between highlightand shadow. Concentrated beams createhigher contrast and deeper shadows,emphasizing form and texture. Frontal light-ing, located 30° to 45° from the center of anobject in the horizontal plane and 30° to 45°from nadir in the vertical plane, modelsobjects in a manner that replicates sunlight.

Lighting a vertical surface behind anobject provides a luminous backdrop to sep-arate the object visually from its background(figure 13.22), much the way an actor isseparated from the scenery on a stage.Lighting an object from the side as well asfrom above provides added dimension to thepiece.

Perception is disturbed when theexpected relationship of highlight andshadow is reversed or when an object islighted from a less conventional angle.Uplighting creates an ominous, ghoulishimpression (see figures 3.27 and 3.28).Backlighting leaves an object in silhouette.

Paintings and Flat Works of ArtFor lighting paintings and flat works of art,two principal methods exist: uniform illumi-nation and nonuniform illumination.

Providing uniform lighting for all verticalsurfaces that will receive art gives promi-nence to the architecture; no hierarchy isestablished among the individual works ofart, allowing viewers to select their ownfocus. Objects can be changed without read-justing the lighting equipment (figure 13.23).

Providing nonuniform lighting focuseslight on individual works while leaving thesurround in comparative darkness. Thisgives prominence to the art over the archi-tecture, creating a more dramatic environ-ment. Every time the art changes, the

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lighting equipment must also be adjusted(figure 13.24).

The placement of the light sourcedepends upon the medium, surface texture,kind of frame, and enclosure (glass or plas-tic) of the object. For flat works mounted ona vertical surface, the optimum location for alight source is usually at an angle of 30° fromnadir (straight down) to average eye level(5 ft 3 in AFF) (figure 13.25).

An aiming angle of less than 30° (morenearly vertical) creates disturbing shadowsfrom the frame and distorts the objectbecause it exaggerates its texture. An aimingangle greater than 30° (more nearly horizon-tal) results in reflected glare from the surfaceof the object, washing out detail. This greaterangle also casts a shadow of the viewer on

the artwork and causes the luminaire to be asource of glare to others moving through thespace.

For nonuniform wall lighting, point-source object lights are ideal. When morethan one luminaire is required because ofthe size of the work to be lighted, the squarerule applies once again: the luminaires arespaced on centers closer than or equal tothe distance away from the wall. The dis-tance from the wall varies with the ceilingheight (figure 13.26).

When a space with nonuniform vertical-surface illumination has frequently changingexhibits, a flexible lighting system is appro-priate. Track systems are often selectedbecause the track luminaires are easy tolocate and aim (focus) as needed. The track

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Figure 13.22 Lighting the vertical surface behind an object.

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Figure 13.23 Uniform illumination for art.

Figure 13.24 Nonuniform illumination for art.

itself also serves as the wireway, providing asimple method of power distribution.

With either method for lighting art,excellent color rendering is essential for theproper appreciation of objects. Continuous-spectrum, high-color-rendering sourcesallow the art to be viewed under spectral dis-tribution conditions similar to those underwhich it was created.

Conservation of MaterialsConservation of materials is a fundamentalconcern in the lighting of art. All organic

material is susceptible to pigment changeand weakening from exposure to light and itsaccompanying heat. In the museum environ-ment, these materials include paper, cotton,linen, parchment, leather, silk, wool, feath-ers, hair, dyes, oils, glues, gums, resins,and—because of similarities in chemicalstructure—almost all synthetic dyes andplastics.

Damage is related to wavelength. Ultra-violet (UV) radiation causes more damage,but much less UV than visible radiation ispresent in all light sources, including day-

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Figure 13.25 Optimum placement for lighting art.

light. A material that is fairly fast (morestable) but nevertheless susceptible todamage, such as the oil in paintings, will bechanged mainly by UV radiation. But moresensitive dyes and pigments, which aredamaged by either UV or visible radiation,

will be changed mainly by the visible radia-tion, since it is more plentiful. In the museumenvironment, it is necessary to limit both UVand visible radiation.

Three steps will help to protect fugitivematerials from the potential damage caused

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Figure 13.26 Typical luminaire mounting locations with 30° aiming angle.

by light and heat: (1) evaluate daylight expo-sure, (2) evaluate electric light exposure,and (3) evaluate duration of exposure.

Evaluate the daylight first, because itcontains a much higher proportion of UVthan do electric sources. The highest-qualityUV filters for daylight are made of acrylic andother plastics formulated to eliminate thetransmission of UV but allow the passage ofvisible light. They are available as self-sup-porting sheets used in place of glass, thinacetate applied to glass, and varnish.

White paint is also a good UV absorber.If all light entering a room is reflected at leastonce from a white surface, the UV problemwill be solved. Titanium dioxide pigment isbest for this purpose, but zinc white is also agood absorber.

Second, evaluate the fluorescent andHID lamps. Although they emit UV radiationless strongly than daylight, all dischargelamps require UV filters. Fluorescent andHID lamps with correlated color tempera-tures above 3100 K need careful attention,because both UV radiation and short-wave-length visible radiation increases with colortemperature. Plastic sheets of UV-absorbingmaterial are available from manufacturers ofcolor filters.

Incandescent lamps emit too little UV torequire a filter. UV radiation from almost allincandescent lamps is less than 0.1 percentof the input wattage. Tungsten-halogenlamps emit slightly more UV below 300 nm,owing to their higher filament temperature.This is still a small amount; fortunately, ordi-nary glass, transparent to longer-wavelengthUV, completely blocks this extra-short emis-sion. (Tungsten-halogen lamps in U.S.luminaires will already have a lens or coverglass that provides safety protection in caseof lamp breakage.)

It is more difficult to limit visible radia-tion than to limit UV radiation because theartwork will then be left in darkness.

Museum practice suggests that for oil andtempera paintings, oriental lacquer, undyedleather, horn, bone, and ivory, maximummaintained illuminance is 15 fc on the sur-face. For objects especially sensitive to light,such as drawings, prints, watercolors, tapes-tries, textiles, costumes, manuscripts, andalmost all natural history exhibits, maximummaintained illuminance is 5 fc.

With the quantity of light maintained at5 to 15 fc, radiant heat is also controlled toreasonable limits. Lamps should be locatedoutside exhibition cases and ventilated withair that avoids traveling directly past theexhibits. Dichroic cool-beam lamps areuseful. Their color appearance is somewhatcooler than standard sources; the color ren-dering, however, is undisturbed.

Third, evaluate the time of exposure.Exposure is the simple product ofilluminance and time. The same amount ofdamage will be produced by a large quantityof illuminance for a short time or a smallquantity of illuminance for a long time. If theilluminance is halved, the rate of damage ishalved. The optimal strategy is to reduceboth illuminance and time of exposure.

With low illuminance values, warmversus cool colors of light are preferred. Thelow quantity of light is less important to theviewer than the balance of brightnessbetween the works of art and the surround(the remaining space). Adaptation plays animportant role in the enjoyment of art: theviewer’s eyes must be adapted to the lowerilluminance before entering the exhibit room.

BALANCE OF BRIGHTNESSIn chapter 2 we learned that lighting designinvolves the balance of three elements oflight: ambient light, focal glow, and sparkle.The balance of these three elements causesa worker’s task to be easily distinguishedfrom the background, an artwork to standout from its surround, and a conference or

229

D E S I G N

restaurant table to be the focus of its partici-pants’ attention. The result is known as thebalance of brightness.

It is often desirable to light oppositewalls in a space, thereby establishing a bal-ance of brightness (figure 13.27). Balanceis different from symmetry: lighting theopposing walls in the same manner isunnecessary, although one may choose todo so. Instead, one wall may be uniformlyilluminated with a wall-wash system and theother will be nonuniformly illuminated withobject lights (figure 13.28).

It is also desirable to balance the perim-eter illumination of a space with its center. Ifa room’s breadth is greater than its height, it

is impossible to light it successfully solelyfrom the walls. When diffusely lighted wallsare distant from each other in a low-ceil-inged space and they are the only source ofillumination, the resulting environment isbland and gloomy. Downlighting is added tothe center; otherwise all persons and objectsin the center of the space will appear in sil-houette (figure 13.29).

Remember that people interpret theoverall environment chiefly through bright-ness relationships. Their subjective impres-sions of visual space are primarily a functionof brightness patterns and pattern organiza-tion—the relationship of surfaces that arelighted or left in relative darkness.

230


Figure 13.27 Lighting opposite walls establishes a balance of brightness.

D E S I G N

Figure 13.28 Lighting opposite walls in different ways also provides a balance of brightness.

Figure 13.29 When lighted walls are distant from each other in a low-ceilinged space, downlighting addded to the centerprovides balance of brightness.

Some lighting patterns affect personal ori-entation and understanding of a room’s sur-faces and objects. Object-lighting and shelf-lighting influence attention and consciousness(figure 13.29); wall-lighting and corner-lightingenhance understanding of room size andshape (figure 13.30). Together, the resultingbalance of brightness establishes or modifiesour sense of enclosure.

Other lighting patterns involve the com-munication of ideas and impressions ofactivity setting or mood. Because the eye isinvoluntarily drawn to bright objects or toareas that contrast with the background,high-contrast settings are effective at direct-

ing attention and interest to selected detailwhile de-emphasizing other objects, areas,or surfaces (figure 13.31).

When the balance of brightness is pur-posefully established, designers provide anappropriate background for the intendedactivity or more: the purposeful manipulationof light can delight, enchant, and commandattention (figure 13.32).

An ExampleIn a restaurant, if the lighting system isdesigned to illuminate horizontal surfaces,such as tabletops, while de-emphasizing thearchitecture, people and activities become

232


Figure 13.30 Wall-lighting and corner-lighting enhance understanding of room size and shape.

233

Figure 13.31 High contrast lighting is effective at directing attention and interest.

Figure 13.32 The purposeful manipulation of light can enchant and command attention.

the dominant feature. This lighting conditionincreases awareness of nearby detail,people, and movement, and encouragesconviviality among patrons. The architecturewill appear as a neutral or subordinate visualinfluence (figure 13.33).

The architectural environment, however,is interpreted by illuminating vertical andoverhead surfaces. When lighting focusesthe visual emphasis on these peripheral sur-faces, the intensity of illumination on thetabletops is reduced; objects and people inthe center fall into silhouette. Activity is thenvisually subordinate to the general space,inducing a more intimate atmosphere inwhich individuals feel a sense of privacy oranonymity (figure 13.34).

Successful restaurant design is the bal-ance of the two: a convivial atmosphere in

which one feels a sense of intimacy and pri-vacy, where other guests at other tablesbecome the background, and where yourtable is the most important one in the room(figure 13.35).

Luminance RatiosIn offices, controlling the luminance varia-tions within limits ensures good visibility.Within these limits, variation is desirable andwill make the office environment morepleasing. Luminance differences are speci-fied in terms of the ratio between one lumi-nance and the other (figure 13.36).

It is undesirable to maintain these ratiosthroughout the entire environment, however.For visual interest and distant eye focus(required for eye muscle relaxation periodi-cally throughout the day), small areas that

234


Figure 13.33 When the lighting system illuminates horizontal surfaces, people and activities become dominant.

235

Figure 13.34 When the lighting system illuminates vertical and overhead surfaces, the architecture becomes dominant.

Figure 13.35 When the lighting system illuminates both horizontal and vertical surfaces, the brightness is balanced.

exceed the luminance ratio recommenda-tions are advantageous. These include art-work, accent finishes on walls or floors,accent finishes on chairs and accessories,and focal lighting.

The perception of brightness dependson surface reflectance as much as it does onilluminance. Consideration of surface finishreflectances is just as important as the light-ing design.

ShadowsLighting design includes shadows as well aslight. Just as musicians make sounds to cap-ture silence and architects develop complexshapes to envelop empty space, lightingdesigners illuminate with shadows (figure13.37).

Light and dark are not antagonistic toeach other. They are counterparts, like the

yin and yang of Chinese cosmology thatcombine to produce all that comes to be.Without shade or darkness, light loses muchof its meaning; patterns of light and shaderender the prominences of surfaces andobjects in the visual field (figure 13.38).

Again, three-dimensional form is per-ceived as a relationship of light and shadow.If a projecting corner formed by the meetingof two white planes is lighted so that the twosides look equally bright, the eye can nolonger discern the edge of the corner. Youmay still recognize it because of the binocu-lar function of your eyes or because you cansee where the two planes intersect otherplanes. But you have lost an essentialmeans of seeing that there is a corner.

It will not help to increase the lightequally on both sides. If the light on one sideis reduced to produce a marked difference in

236


Figure 13.36 Maximum luminance ratios recommended for a VDT workstation.

the two planes, however, the cornerbecomes evident, even if the total intensityof light has decreased.

Only with shadows, then, can much oflight be appreciated. Just as a good listenerappreciates conversation by its pauses, wecan appreciate light by its shadows.

ENERGY-EFFECTIVE DESIGNSuccessful lighting design is energy-effectivedesign. It uses the available watts to supplylight where it is needed, when it is needed,and limits light from where it is unwanted(figure 13.39). Energy-effective designincludes both careful control of light and

careful control of brightness. It meansmaking every watt count (figure 13.40).

Energy efficiency and lighting qualityhave sometimes been considered conflictingdesign objectives. Energy limits are just oneof the many design constraints that design-ers face. Design means working within pro-ject parameters, whether they are spacelimitations, fixed budgets, time constraints,color palettes, or connected lighting powerlimits (figure 13.41).

Within a given power budget, thedesigner has unlimited freedom. Distributinglight on room surfaces and objects in a waythat facilitates orientation, aids perception,

237

D E S I G N

Figure 13.37 Lighting design includesshadows as well as light.

238Figure 13.39 Energy-effective design uses the available watts to supply light where it is needed.

Figure 13.38 Patterns of light andshade render the prominences ofsurfaces and objects in the visualfield.

239

D E S I G N

Figure 13.40 Energy-effective design includes carefulcontrol of light and brightness.

Figure 13.41 Design means working within the projectparameters

and supports activities, is another way ofsaying that limited lighting watts are beingdistributed in the most effective way (figure13.42). Stringent energy codes simplyrequire more careful design to establish visu-ally satisfying environments that also meetregulatory requirements.

INTEGRATING LIGHT ANDARCHITECTURETo be successful, lighting design is integratedinto the fabric of the architecture. It inte-grates the lighting concept with the architec-tural one (figure 13.43); it integrates the

technology that produces light with themechanical and structural systems that erectthe building (figure 13.44). The objective is touse modern lighting techniques in a mannersympathetic to, and expressive of, the spirit ofthe architectural concept (figure 13.45).

When light and architecture are inte-grated, we are not aware of the mechanicsof light production—only of a comfortableenvironment that encourages productivityand enhances well-being. Because lightinfluences our sense of well-being, we areultimately concerned with not only the qual-ity of light, but the quality of life.

240


Figure 13.42 Limited lighting wattsdistributed in an effective way.

241

Figure 13.44 Integrating the lighting technology with the mechanical and structural systems.

Figure 13.43 Integrating the lighting concept with the architectural concept.

242


Figure 13.45 Modern lighting techniques used in a manner sympathetic to and expressive of the spirit of the architecturalconcept

Appendix

TABLE 1

TYPICAL COLOR RENDERING INDICES

Lamp Description

Color Rendering

Index (CRI)

Color Temperature

in Kelvin (K)

Incandescent and Tungsten-Halogen

Incandescent 100 2800

Light blue incandescent 100 4000

Daylight incandescent 100 5000

Tungsten-halogen 100 3100

Tungsten-halogen with light blue filter 100 4000

Tungsten-halogen with blue filter 100 5000

Fluorescent

Cool white 62 4100

Cool white deluxe 89 4100

Warm white 53 3000

Warm white deluxe 85 3000

Natural 90 3700

Lite white 51 4200

Daylight 79 6500

Daylight Deluxe 84 6500

Cool green 70 6450

RE–730 70–79 3000

RE–735 70–79 3500

RE–741 70–79 4100

RE–750 70–79 5000

RE–830 80–89 3000

RE–835 80–89 3500

RE–841 80–89 4100

RE–850 80–89 5000

RE–930 95 3000

RE–950 98 5000

Chroma 50 92 5000

Chroma 75 95 7500

T8/ADV/830 80–89 3000

T8/ADV/835 80–89 3500

244


Lamp Description

Color Rendering

Index (CRI)

Color Temperature

in Kelvin (K)

T8/ADV/841 80–89 4100

T8/ADV/850 80–89 5000

T12/ADV/830 82 3000

T12/ADV/835 82 3500

T12/ADV/841 82 4100

T12/ADV/850 82 5000

High-Intensity Discharge

Standard mercury 20 5900

Mercury deluxe white 45 3900

Standard metal halide 65 4000

Standard coated metal halide 70 3800

Cool ceramic metal halide (39-70 W) 92 4000

Cool ceramic metal halide (100-400 W) 93 4000

Warm ceramic metal halide (39-70 W) 82 3000

Warm ceramic metal halide (100 W) 85 3000

Combined metal halide/HPS 90 4000

Standard high-pressure sodium 22 2000

Deluxe high-pressure sodium 65 2200

White high-pressure sodium 85 2700

Low-pressure sodium 0 1700

245

A P P E N D I X

TABLE 2

INCANDESCENT LAMP DESIGNATIONS AND PROPERTIES

ANSI LampDesignation

DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

Aluminum reflector (AR) lamps

15ALR18/NSP6 (GBA) 6 15 2,000 5,200 6° —

15ALR18/SP14 (GBC) 6 15 2,000 1,900 14° —

20ALR12/NSP6 (GBD) 12 20 2,000 6,400 6° —

20ALR12/SP18 (GBE) 12 20 2,000 1,000 18° —

20ALR12/FL34 (GBF) 12 20 2,000 350 34° —

—

50ALR18/SP10 (GBJ) 12 50 2,000 12,000 10° —

50ALR18/NFL22 (GBK) 12 50 2,000 2,000 22° —

—

20AR70/SP8 12 20 3,000 7,700 8° — Filament shield

20AR70/FL25 12 20 3,000 900 25° — Filament shield


50AR70/FL25 12 50 3,000 2,600 25° — Filament shield

35AR111/SSP4/6V 6 35 3,000 30,000 4° — Filament shield

35AR111/SSP4 12 35 3,000 45,000 4° — Filament shield



50AR111/SSP4 12 50 3,000 50,000 4° — Filament shield





75AR111/WFL45 12 75 3,000 1,700 45° — Filament shield



100AR111/WFL45 12 100 3,000 2,800 45° — Filament shield

Mirror-reflector (MR) lamps

20MR11/SP10 (FTB) 12 20 4,000 5,500 10° —

246



DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

20MR11/SP15 (FTC) 12 20 3,500 1,760 15° —

20MR11/FL35 (FTD) 12 20 4,000 700 35° —

35MR11/SP10 (FTE) 12 35 4,000 8,500 10° —

35MR11/SP15 (FTF) 12 35 3,500 3,000 15° —

35MR11/FL40 (FTH) 12 35 4,000 1,500 40° —

20MR16/NSP8 (ESX) 12 20 4,000 6,000 8° —

20MR16/FL40 (BAB) 12 20 4,000 700 40° 59°

20MR16/VWFL60 12 20 4,000 350 60° —

20MR16/IR/SP8 12 20 5,000 6,500 8° — IR-reflecting

20MR16/IR/FL36 12 20 5,000 1,000 36° — IR-reflecting

35MR16/NSP8 (FRB) 12 35 4,000 11,000 10° —

35MR16/SP20 (FRA) 12 35 4,000 2,800 20° —

35MR16/FL40 (FMW) 12 35 4,000 1,400 40° —

35MR16/VWFL60 12 20 4,000 650 60° —


35MR16/IR/NFL24 12 35 5,000 4,400 24° — IR-reflecting


35MR16/IR/WFL60 12 35 5,000 1,050 60° — IR-reflecting







45MR16/IR/WFL60 12 45 5,000 1,300 60° — IR-reflecting

50MR16/NSP10 (EXT) 12 50 4,000 11,500 10° 24°

50MR16/NFL25 (EXZ) 12 50 4,000 3,200 27° 49°

50MR16/NFL30 (EXK) 12 50 4,000 2,500 32° 52°

50MR16/FL40 (EXN) 12 50 4,000 2,000 40° 64°

50MR16/WFL60 (FNV) 12 50 4,000 1,000 60° —




65MR16/NSP10 (FPA) 12 65 4,000 14,000 10° —

247

A P P E N D I X


DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

65MR16/NFL25 12 65 4,000 4,000 25° —

65MR16/FL40 (FPB) 12 65 4,000 2,100 40° —

65MR16/VWFL60 12 65 4,000 1,050 60° —

71MR16/NSP15 (EYF) 12 71 4,000 11,500 15° —

71MR16/NFL25 (EYJ) 12 71 4,000 5,500 25° —

71MR16/FL40 (EYC) 12 71 4,000 2,200 40° —

75MR16/SP10 (EYF) 12 75 4,000 14,000 10° —

75MR16/FL36 (EYC) 12 75 4,000 2,500 36° —

Parabolic aluminum reflector (PAR) lamps

35PAR14/H/FL 120 35 2,000 85 50° —

45PAR16/H/NSP10 120 45 2,000 5,000 10° —

45PAR16/H/NFL27 120 45 2,000 1,400 27° —

50PAR16/H/FL40 120 50 2,000 800 40° —

60PAR16/H/NSP10 120 60 2,000 5,700 10° —

60PAR16/H/NFL27 120 60 2,000 2,000 27° —

75PAR16/H/NSP10 120 75 2,000 7,500 10° —

75PAR16/H/NFL30 120 75 2,000 1,900 30° —

35PAR20/H/NSP10 120 35 2,500 3,000 10° —

35PAR20/H/NFL30 120 35 2,500 800 30° —

35PAR20/H/WFL40 120 35 2,500 500 40° —

50PAR20/H/NSP9 120 50 2,000 6,200 9° —

50PAR20/H/SP16 120 50 2,000 3,200 16° —

50PAR20/H/NFL30 120 50 2,000 1,400 30° —

50PAR20/H/WFL40 120 50 2,500 900 40° —

35PAR30L/H/NSP9 120 35 2,500 5,700 9° —

35PAR30L/H/WFL50 120 35 2,500 450 50° —

45PAR30/HIR/SP9XL 120 45 6,000 9,750 9° — IR-reflecting

45PAR30/HIR/FL25XL 120 45 6,000 2,025 25° — IR-reflecting


50PAR30/H/NSP10 120 50 3,000 8,250 10° —

50PAR30/H/NFL30 120 50 2,000 1,950 30° —

248



DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

50PAR30/H/FL40 120 50 2,000 1,500 40° —

50PAR30/HIR/NSP9 120 50 3,000 13,000 9° — IR-reflecting

50PAR30/HIR/NFL25 120 50 3,000 2,900 25° — IR-reflecting

50PAR30/HIR/FL35 120 50 3,000 1,500 35° — IR-reflecting

50PAR30L/H/NSP9 120 50 2,000 8,800 9° —

50PAR30L/H/SP16 120 50 2,000 4,200 16° —

50PAR30L/H/NFL30 120 50 2,000 1,900 30° —

50PAR30L/H/FL40 120 50 2,000 1,250 40° —

50PAR30L/H/WFL60 120 50 2,000 550 60° —

60PAR30/H/NSP10 120 60 2,500 10,000 10° —

60PAR30/H/NFL30 120 60 2,500 2,800 30° —

60PAR30/H/FL40 120 60 2,500 1,850 40° —

75PAR30/H/NSP10 120 75 2,000 15,400 10° —

75PAR30/H/NFL25 120 75 2,000 3,100 27° —

75PAR30/H/FL35 120 75 2,000 2,000 35° —

75PAR30L/H/NSP9 120 75 2,000 15,400 9° —

75PAR30L/H/SP16 120 75 2,000 6,700 16° —

75PAR30L/H/NFL30 120 75 2,000 3,400 30° —

75PAR30L/H/FL40 120 75 2,000 2,200 40° —

75PAR30L/H/WFL60 120 75 2,500 1,100 50° —

25PAR36/VNSP5 6 25 1,000 19,700 — 5.5° × 4.5° Filament shield

25PAR36/NSP9 12 25 2,000 2,600 10° × 8° 19° × 17° Filament shield

25PAR36/WFL30 12 25 2,000 360 37° × 26° 49° × 41° Filament shield

25PAR36/VWFL55 12 25 2,000 160 55° — Filament shield

35PAR36/H/VNSP5 12 35 4,000 25,000 5° —

35PAR36/H/NSP8 12 35 4,000 20,000 8° —

35PAR36/H/WFL30 12 35 4,000 900 25° × 35° —

36PAR36/H/VNSP5 12 36 4,000 17,000 5° —

36PAR36/H/NSP13 12 36 4,000 3,500 13° —

36PAR36/H/WFL32 12 36 4,000 1,000 32° —

50PAR36/NSP6 12 50 4,000 25,000 6° — Filament shield

50PAR36/NSP10 12 50 2,000 1,100 10° 20° × 17° Filament shield

50PAR36/WFL35 12 50 2,000 1,300 37° × 27° 48° × 41° Filament shield

50PAR36/VWFL55 12 50 2,000 1,100 55° 80° × 80° Filament shield

249

A P P E N D I X


DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

50PAR36/H/NSP5 12 50 4,000 35,000 5° —

50PAR36/H/NSP8 12 50 4,000 30,000 8° —

50PAR36/H/WFL30 12 50 4,000 1,300 25° × 35° —

45PAR38/H/NSP9 120 45 2,500 10,000 9° —

45PAR38/H/SP11 120 45 2,500 8,800 11° —

45PAR38/H/FL30 120 45 2,500 1,500 32° —



50PAR38/HIR/SP6 120 50 3,000 20,000 6° — IR-reflecting


50PAR38/HIR/S/SP10 120 50 4,000 14,000 10° — IR, silverizedreflector

50PAR38/HIR/S/FL25 120 50 4,000 3,000 25° — IR, silverizedreflector





60PAR38/HIR/S/SP12 120 60 4,000 20,000 12° — IR, silverizedreflector



60PAR38/HIR/WFL55 120 60 3,000 1,250 53° — IR-reflecting



75PAR38/H/NSP8 120 75 2,500 18,400 8° —

75PAR38/H/NFL25 120 75 2,500 4,000 26° —




90PAR38/H/SP10 120 90 2,000 18,500 12° —

90PAR38/H/NFL25 120 90 2,000 4,000 25° —

90PAR38/H/3WSP12 120 90 2,500 14,300 12° Side-prong base

90PAR38/H/3FL30 120 90 2,500 3,500 30° Side-prong base

90PAR38/CB/H/FL25 120 90 2,500 4,100 25° Cool-beam

250



DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%



100PAR38/H/SP10 120 90 2,000 17,000 10°

100PAR38/H/FL25 120 90 2,000 4,800 25°




120PAR38/3SP 120 120 2,000 9,200 18° Side-prong base

120PAR38/3FL 120 120 2,000 3,600 30° Side-prong base

120PAR38/H/SP10 120 120 3,000 22,500 10° —

120PAR38/H/NFL25 120 120 3,000 7,700 25°

120PAR38/H/FL30 120 120 3,000 4,600 30° —

120PAR38/H/WFL55 120 120 3,000 2,000 55° —

150PAR38/2FL 120 120 2,000 3,400 24° 60° Cool-beam

150PAR38/3SP 120 120 2,000 10,500 12° 30° Side-prong base

150PAR38/3FL 120 120 2,000 3,400 24° 60° Side-prong base

Q250PAR38/SP10 120 250 4,500 46,500 11° —

Q250PAR38/FL30 120 250 4,500 9,000 22° —

25PAR46/NSP5 6 25 1,000 55,000 — 5.5° × 4.5° Filament shield

150PAR46/3MFL 125 150 2,000 8,000 26° × 13° 39° × 25° Side-prong base

200PAR46/3NSP 120 200 2,000 31,000 12° × 8° 23° × 19° Side-prong base

200PAR46/3MFL 120 200 2,000 11,500 27° × 13° 40° × 24° Side-prong base

120PAR56/VNSP 12 120 2,000 60,000 8° × 6° 15° × 10°

120PAR56/MFL 12 120 2,000 19,000 18° × 9° 29° × 15°

120PAR56/WFL 12 120 2,000 5,625 35° × 18° 50° × 25°

200PAR56/MFL 120 200 2,000 15,000 22° × 13° 34° × 22°

240PAR56/VNSP 12 240 2,000 140,000 90° × 6° 17° × 10°

240PAR56/MFL 12 240 2,000 46,000 19° × 8° 28° × 15°

240PAR56/WFL 12 240 2,000 13,000 35° × 18° 50° × 27°

300PAR56/NSP 120 300 2,000 68,000 10° × 8° 20° × 14°

300PAR56/MFL 120 300 2,000 24,000 23° × 11° 34° × 19°

300PAR56/WFL 120 300 2,000 11,000 37° × 18° 57° × 27°

Q500PAR56/NSP 120 500 4,000 96,000 13° × 8° 32° × 15°

251

A P P E N D I X


DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

Q500PAR56/MFL 120 500 4,000 43,000 26° × 10° 42° × 20°

Q500PAR56/WFL 120 500 4,000 19,000 44° × 20° 66° × 34°

500PAR64/NSP 120 500 2,000 110,000 12° × 7° 19° × 14°

500PAR64/MFL 120 500 2,000 45,000 9° × 25° 35° × 19°

500PAR64/WFL 120 500 2,000 10,500 20° × 55° 55° × 32°

Q1000PAR64/NSP 120 1,000 4,000 135,000 8° × 20° 31° × 14°

Q1000PAR64/MFL 120 1,000 4,000 82,000 10° × 30° 45° × 22°

Q1000PAR64/WFL 120 1,000 4,000 23,000 20° × 60° 72° × 45°

Reflector (R) lamps

15R14SC/SP 12 15 2,000 135 14° — Single contact base

25R14SC/SP15 12 25 2,000 1,200 16° 32° Single contact base

25R14SC/FL35 12 25 2,000 200 36° 102° Single contact base

25R14/WFL60 120 25 1,500 150 60° 120°

50BR19/25/SP 120 50 2,000 — 25° —

30R20/FL40 120 30 2,000 300 38° —

50R20/FL40 120 50 2,000 550 38° —

75R20/FL120 120 75 2,000 800 — 120°

100BR25/25 120 100 2,000 — 25° —

65BR30/SP20 120 65 2,000 1,625 20° —

65BR30/SP20XL 120 65 2,500 1,575 20° —

65BR30/FL55 120 65 2,000 525 55° —

65BR30/FL55XL 120 65 2,500 510 55° —

85BR30/SP20 120 85 2,000 3,100 20° —

85BR30/FL55 120 85 2,000 700 55° —

65BR40/FL60 120 65 2,000 500 60° —

85BR40/SP20 120 85 2,000 3,100 20° —

85BR40/FL60 120 85 2,000 700 60° —

252



DesignVolts Watts

DesignLife

(Hrs.)

InitialCandle-power

Beam-Spread

Notes50% 10%

120BR40/SP20 120 120 2,000 4,600 20° —

120BR40/FL60 120 120 2,000 1,000 60° —

300R40/SP40 120 300 2,000 14,000 40° —

300R40/FL120 120 300 2,000 2,900 120° —

Elliptical reflector (ER) lamps

50ER30/FL30 120 50 2,000 1,300 28° 70°

75ER30/FL30 120 75 2,000 1,800 28° 70°

120ER30/FL30 120 120 2,000 2,900 28° 70°

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TABLE 3

FLUORESCENT LAMP DESIGNATIONS AND PROPERTIES

Lamp Description DesignationImpres-

sion

LightOutput

(%)

ColorTemper-ature inKelvin

(K)

ColorRender-ing Index

(CRI)Life

(Hours)Initial

LumensMean

Lumens

Cool white CW Cool 100 4100 62 20,000+ 3,050 2,650

Cool white deluxe CWX Cool 72 4100 89 20,000+ 2,200 1,800

Warm white WW Warm 102 3000 52 20,000+ 3,100 2,700

Warm white deluxe WWX Warm 68 2800 77 20,000+ 2,200 1,805

Soft white SW Warm 68 3000 79 20,000+ 2,150 1,800

Natural N Neutral 69 3700 90 20,000+ 2,100 1,870

Lite white LW Cool 102 4200 51 20,000+ 3,050 2,650

Daylight D Daylight 83 6500 79 20,000+ 2,600 2,250

Daylight Deluxe DX Daylight 76 6500 84 20,000+ 2,300 2,000

RE–730 730 Warm 105 3000 70 20,000+ 3,200 2,880

RE–735 735 Neutral 105 3500 73 20,000+ 3,200 2,880

RE–741 741 Cool 105 4100 70 20,000+ 3,200 2,880

RE–750 750 Daylight 90 5000 76 20,000+ 3,200 2,880

RE–830 830 Warm 108 3000 85 20,000+ 3,300 2,970

RE–835 835 Neutral 108 3500 85 20,000+ 3,300 2,970

RE–841 841 Cool 108 4100 85 20,000+ 3,300 2,970

RE–850 850 Daylight 93 5000 85 20,000+ 3,280 2,950

RE–930 930 Warm 66 3000 95 20,000+ 2,100 1,870

RE–950 950 Daylight 66 5000 98 20,000+ 2,100 1,870

Chroma 50 C50 Daylight 72 5000 92 20,000+ 2,200 1,915

Chroma 75 C75 Daylight 66 7500 95 20,000+ 2,000 1,720

T8/ADV/830 ADV830 Warm 105 3000 86 20,000+ 3,300 2,970

T8/ADV/835 ADV835 Neutral 105 3500 86 20,000+ 3,300 2,970

T8/ADV/841 ADV841 Cool 105 4100 86 20,000+ 3,300 2,970

T8/ADV/850 ADV850 Daylight 105 5000 86 20,000+ 3,300 2,970

T12/ADV/830 ADV30 Warm 118 3000 82 20,000+ 3,600 3,100

T12/ADV/835 ADV35 Neutral 118 3500 82 20,000+ 3,600 3,100

T12/ADV/841 ADV41 Cool 118 4100 82 20,000+ 3,600 3,100

T12/ADV/850 ADV50 Daylight 118 5000 82 20,000+ 3,600 3,100

Red R — 6 — — 20,000+ 195 60

Pink PK — 35 — — 20,000+ 1,160 695

Gold GO — 60 — — 20,000+ 2,400 1,765

Green G — 140 — — 20,000+ 4,400 2,200

Blue B — 35 — — 20,000+ 1,200 720

254

TABLE 4

EFFICACY OF ELECTRIC LIGHT SOURCES

Lamp TypeWattageRange

Initial LampEfficacy (Lumens

per watt)

ColorTemperaturein Kelvin (K)

ColorRenderingIndex (CRI)

Design Life

(Hours)

Incandescent 6–1,500 4–24.5 2700–2800 100 750–4,000

Tungsten-halogen 5–1,500 10–22 2900–3100 100 1,000–6,000

Fluorescent 4–215 10–104.5 2700–7500 53–95 6,000–24,000+

Compact fluorescent 5–80 28–76 2700–4100 81–82 6,000–14,000

Mercury vapor 40–1,000 19–59 3300–5900 15–52 12,000–24,000+

Metal halide 32–1,500 35–100 3000–4400 65–96 3,000–20,000

High-pressure sodium 33–1,000 31–127 1800–2800 22–85 7,500–24,000+

Low-pressure sodium 18–180 58–185 1740–1750 0 14,000–18,000

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TABLE 5

COMPARATIVE LUMINANCE OF INCANDESCENT AND FLUORESCENT LAMPS(APPROXIMATE CANDELAS PER SQUARE INCH)

Lamp Description Shape Characteristics Luminance (cd/sq in)

Incandescent

150 W A21 (IF) 150.0

Fluorescent

Preheat

8 W T5 (12") 8.1

15 W T8 (18") 6.7

15 W T12 (18") 4.1

20 W T12 (24") 4.6

Rapid Start

30 W T12 (36") 5.3

32 W T8 (48") 7.4

40 W T8 (60") 7 4

40 W T12 (48") 5.4

40 W T12 (48" ES) 4.7

40 W T12 (22716" U-bent) 5.0

High Output

24" T12 (35 W) 6.1

48" T12 (60 W) 7.3

72" T12 (85 W) 7.3

96" T12 (110 W) 7.3

96" T12 (95 W ES) 6.6

Very High Output

48" T12 (116 W) 12.0

72" T12 (162 W) 12.0

96" T12 (212 W) 12.0

96" T12 (185 W ES) 11.2

Instant Start

40 W T12 (48") 5.3

40 W T12 (60") 2.3

Slimline

42" T8 (23 W) 5.3

64" T8 (35 W) 5.3

256


Lamp Description Shape Characteristics Luminance (cd/sq in)

72" T8 (37.5 W) 5.0

96" T8 (50 W) 5.0

48" T12 (38.5 W) 5.0

72" T12 (56 W) 5.0

96" T12 (75 W) 5.0

96" T12 (60W ES) 4.5

Circline

20 W T9 (6½” dia.) 5.9

22 W T9 (8¼" dia.) 5.2

32 W T9 (12" dia.) 4.8

40 W T9 (16" dia.) 4.8

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TABLE 6

RELATIVE OUTPUT OF COLORED LAMPS

Lamp Color Description Light Output (%) Lamp Color Description Light Output (%)

Incandescent—tinted lamps Fluorescent

Clear 100 Cool white 100

White 85 Cool white deluxe 72

Ivory 73 Warm white 102

Flame tint 58 Warm white deluxe 72

Rose 35 Natural 69

Red 5 Lite white 104

Orange 35 Daylight 85

Yellow 65 Daylight Deluxe 76

Green 5 RE-730 93

Blue 3 RE-735 93

RE-741 93

Incandescent—sign lamps RE-750 90

Clear 100 RE-830 98

White 85 RE-835 98

Ivory 73 RE-841 98

Flame tint 58 RE-850 97

Rose 35 RE-930 66

Red 5 RE-950 66

Orange 35 Chroma 50 72

Yellow 65 Chroma 75 66

Green 5 T8/ADV/830 105

Blue 3 T8/ADV/835 105

T8/ADV/841 105

Lumiline lamps T8/ADV/850 105

Clear 100 T12/ADV/830 118

White 85 T12/ADV/835 118

T12/ADV/841 118

T12/ADV/850 118

Blue 39

Gold 79

Red 6

Pink 45

Green 160

Deep blue 17

258


TABLE 7

RELATIVE LAMP WATTS FOR APPROXIMATE EQUAL QUANTITY OF LIGHT

Filament (clear color) 30 W Clear

60 W Pink

90 W Blue-white

200 W Red

90 W Amber

36 W Yellow or gold

300 W Green

300 W Blue

Filament (diffuse color) 30 W Silica coat

39 W Pink tint

36 W Gold tint

60 W Green tint

75 W Blue tint

Fluorescent 10 W Cool white

22 W Pink

165 W Red

13 W Yellow or gold

11 W Yellow-green

6 W Green

22 W Blue

65 W Deep blue

TABLE 8

RELATIVE BRIGHTNESSFOR EQUAL ATTRACTION

White light 10

Yellow light 12

Red light 3

Green light 4

Blue light 6

259

A P P E N D I X

TABLE 9

RECOMMENDED WIRE SIZE AND SECONDARY WIRE LENGTH FOR LIGHTING CIRCUITSUSING 120 V PRIMARY/12 V SECONDARY TRANSFORMERS

Wire

Size

(Gauge)

Watts (VA) per Circuit

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500

Maximum Secondary Wire Length in Feet

14 75 37 25 19 15 12 11 9 8 7 7 6 6 5 5 5 4 4 4 4 4 3 3 3 3

12 118 59 39 30 24 20 17 15 13 12 11 10 9 8 8 7 7 7 6 6 6 5 5 5 5

10 188 94 63 47 38 31 27 24 21 19 17 16 14 13 13 12 11 10 10 9 9 9 8 8 8

8 299 149 100 75 60 50 43 37 33 30 27 25 23 21 20 19 18 17 16 15 14 14 13 12 12

6 476 238 159 119 95 79 68 60 53 48 43 40 37 34 32 30 28 26 25 24 23 22 21 20 19

This chart is based on SPT-3 wire and a maximum 0.63 voltage drop at the end of the run.

Exceeding the maximum secondary wire lengths noted in the chart above will cause the voltage to drop along the length of the wire.Lamps positioned closer to the transformer will burn at a higher color temperature than those farther from it because the lampsnearest the transformer are receiving greater voltage than those farther away.

When dimming low-voltage loads, use dimmers designed for low-voltage magnetic loads with magnetic transformers and dimmersdesigned for electronic low-voltage loads with electronic transformers.

Based on the Recommended Wire Size and Voltage Drop chart from Acme Electric Corporation Catalog ATD-01. Used withpermission from the Acme Electric Corporation Power Distribution Products Division.

260


TABLE 10

TRIGONOMETRIC FUNCTIONS: SINES AND COSINES OF ANGLES

θ° sin θ cos θ θ° sin θ cos θ θ° sin θ cos θ θ° sin θ cos θ

0 0.0000 1.000 22 .375 0.927 45 .707 .707 68 .927 .375

23 .391 .921 46 .719 .695 69 .934 .358

1 .0175 1.000 24 .407 .914 47 .731 .682 70 .940 .342

2 .0349 0.999 25 .423 .906 48 .743 .669

3 .0523 .999 26 .438 .899 49 .755 .656 71 .946 .326

4 .0698 .998 27 .454 .891 50 .766 .643 72 .951 .309

5 .0872 .996 28 .470 .833 73 .956 .292

6 .105 .995 29 .485 .875 51 .777 .629 74 .961 .276

7 .122 .993 30 .500 .866 52 .788 .616 75 .966 .259

8 .139 .990 53 .799 .602 76 .970 .242

9 .156 .988 31 .515 .857 54 .809 .588 77 .974 .225

10 .174 .985 32 .530 .848 55 .819 .574 78 .978 .208

33 .545 .839 56 .829 .559 79 .982 .191

11 .191 .982 34 .559 .829 57 .839 .545 80 .985 .174

12 .208 .978 35 .574 .819 58 .848 .530

13 .225 .974 36 .588 .809 59 .857 .515 81 .988 .156

14 .242 .970 37 .602 .799 60 .866 .500 82 .990 .139

15 .259 .966 38 .616 .788 83 .993 .122

16 .276 .961 39 .629 .777 61 .875 .485 84 .995 .105

17 .292 .956 40 .643 .766 62 .883 .470 85 .996 .0872

18 .309 .951 63 .891 .454 86 .9976 .0698

19 .326 .946 41 .656 .755 64 .899 .438 87 .9986 .0523

20 .342 .940 42 .669 .743 65 .906 .423 88 .9994 .0349

43 .682 .731 66 .914 .407 89 .9998 .0175

21 .358 .934 44 .695 .719 67 .921 .391 90 1.0000 0.0000

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TABLE 11

LAMP LUMEN DEPRECIATION FACTORS

Lamp Description Shape Nominal WattageLamp Lumen Depreciation

(LLD) Factors

Incandescent

Extended service A, PS 15–70 0.85

General service A, PS, S To 40 0.85

50–1,500 0.89

Projector PAR 38-64 75–1,000 0.84

Reflector R40 150–500 0.86

R52-57 500–1,000 0.81

Rough service A, PS 50–200 0.79

Showcase T10 25–40 0.78

Silver-bowl A, PS 200–500 0.75

Three-way A, T 30–150 0.85

PS 100–300 0.72

Tungsten-halogen T 200–1,500 0.96

Vibration A19 50 0.72

Fluorescent

Cool white T12 40 0.87

Cool white deluxe T12 40 0.82

Warm white T12 40 0.87

Warm white deluxe T12 40 0.82

Natural T12 40 0.89

Lite white T12 40 0.87

Daylight T12 40 0.87

Cool green T12 40 0.82

RE-700 series T8 40 0.90

RE-800 series T8 25–40 0.93

T12 30–40 0.90

Chroma 50 T12 40 0.87

Chroma 75 T12 40 0.86

262


Lamp Description Shape Nominal WattageLamp Lumen Depreciation

(LLD) Factors

Fluorescent, continued

Compact, twin-tube T4 5 0.84

Compact, twin-tube T4 7–13 0.85

Compact, quad-tube T4 13–26 0.85

Compact, triple-tube T4 18–70 0.85

Compact, long twin-tube T5 18–80 0.90

High-intensity discharge

Standard mercury clear E28 250 0.88

Mercury warm deluxe white E28 250 0.81

Mercury deluxe white E28 250 0.81

Standard clear metal halide E28 175 0.74*

0.69**

BT56 1,000 0.76

Standard coated metal halide E28 175 0.71*

0.65**

BT56 1,000 0.76

Ceramic metal halide T7 150 0.89

Ceramic metal halide T8 250 0.80

Ceramic metal halide T6½ 70 0.82

Deluxe high-pressure sodium B17 70 0.80

White high-pressure sodium B17 95 0.80

Low-pressure sodium T16 55 0.87

*Vertical lamp orientation

**Horizontal lamp orientation

263

A P P E N D I X

TABLE 12

LUMINAIRE MAINTENANCE CATEGORIES

PROCEDURE FOR DETERMINING LUMINAIRE MAINTENANCE CATEGORIES

To assist in determining luminaire dirt depreciation (LDD) factors, luminaires are separated into six maintenancecategories (I through VI). To arrive at categories, luminaires are arbitrarily divided into sections—a top enclosure and abottom enclosure—by drawing a horizontal line through the light center of the lamp or lamps. The characteristicslisted for the enclosures are then selected as best describing the luminaire. Only one characteristic for the topenclosure and one for the bottom enclosure are used in determining the category of a luminaire. Percentage ofuplight is based on 100% light output for the luminaire. The maintenance category is determined by thecharacteristics in both enclosure columns. If a luminaire falls into more than one category, the lower-numberedcategory is used.

Maintenance Category Top Enclosure Bottom Enclosure

I 1. None 1. None

II 1. None 1. None

2. Transparent with 15% or more uplightthrough apertures

2. Louvers or baffles

3. Translucent with 15% or more uplightthrough apertures

4. Opaque with 15% or more uplightthrough apertures

III 1. Transparent with less than 15% upwardlight through apertures

1. None

2. Translucent with less than 15% upwardlight through apertures

2. Louvers or baffles

3. Opaque with less than 15% upwardlight through apertures

IV 1. Transparent unapertured 1. None

2. Translucent unapertured 2. Louvers or baffles

3. Opaque unapertured

V 1. Transparent unapertured 1. Transparent unapertured

2. Translucent unapertured 2. Translucent unapertured


VI 1. None 1. Transparent unapertured

2. Transparent unapertured 2. Translucent unapertured

3. Translucent unapertured 3. Opaque unapertured


Reprinted from the IES Lighting Handbook, 9th Ed. Used with permission from the Illuminating Engineering Society ofNorth America.

264


265

Reprinted from the IES Lighting Handbook, 9th Ed. Used with permission from the Illuminating Engineering Society of NorthAmerica.

TABLE 13

LUMINAIRE DIRT DEPRECIATION (LDD) FACTORS FOR SIX LUMINAIRE CATEGORIES (ITHROUGH VI) AND FOR FIVE DEGREES OF DIRTINESS

TABLE 14

SAMPLE COEFFICIENT OF UTILIZATION TABLE

Note: the coefficient of utilization values in this table are based on relative photometry which assumes a ballastfactor of 1.0. Any calculations prepared from these data should include an appropriate ballast factor.

266


Coefficients of Utilization—Zonal Cavity Method Effective Floor Cavity Reflectance 0.20

RC 80 70 50 30 10 0

RW 70 50 30 10 70 50 30 10 50 30 10 50 30 10 50 30 10 0

0 86 86 86 86 84 84 84 84 80 80 80 77 77 77 74 74 74 72

1 82 80 78 76 80 78 76 75 75 74 72 72 71 70 70 69 68 67

2 77 74 71 68 76 72 70 67 70 68 66 68 66 64 66 64 63 62

3 73 68 64 61 71 67 63 60 65 62 59 63 61 58 61 59 58 56

4 69 63 58 55 67 62 58 55 60 57 54 59 56 53 57 55 53 51

5 64 58 53 49 63 57 52 49 55 52 49 54 51 48 53 50 48 47

6 60 53 48 44 59 52 48 44 51 47 44 50 46 44 49 46 43 42

7 56 48 43 39 55 48 43 39 47 42 39 46 42 39 45 41 39 38

8 52 44 39 35 51 43 38 35 42 38 35 42 38 35 41 37 34 33

9 48 39 34 31 47 39 34 31 38 34 31 38 33 31 37 33 30 29

10 44 36 30 27 43 35 30 27 35 30 27 34 30 27 33 29 27 26

TABLE 15

RECOMMENDED ILLUMINANCE VALUES

General Lighting Task Lighting

PublicSpaces

SimpleOrien-tation

Occa-sionalVisualTask

LargeVisualTask

SmallVisualTask

VerySmallVisualTask

Activity 3 fc 5 fc 10 fc 30 fc 50 fc 100 fc

GENERAL

Circulation

Corridors •

Elevators •

Lobbies •

Stairs •

Service

Toilets and washrooms •

Storage

Active •

Inactive •

HOSPITALITY FACILITIES

Bathrooms, for grooming •

Bedrooms, for reading •

Cleaning •

Dining •

Kitchen, critical seeing •

Laundry •

Sewing •

INDUSTRY

Assembly

Simple •

Moderately difficult •

Difficult •

Inspection

Simple •

Moderately difficult •

Difficult •

Locker rooms •

A P P E N D I X

267

General Lighting Task Lighting

PublicSpaces

SimpleOrien-tation

Occa-sionalVisualTask

LargeVisualTask

SmallVisualTask

VerySmallVisualTask

Activity 3 fc 5 fc 10 fc 30 fc 50 fc 100 fc

OFFICES

Accounting • *

Conference rooms •

Drafting, high contrast •

Drafting, low contrast •

General/private offices • **

Lounges and reception •

RESIDENCES

Bathrooms, for grooming •

Bedrooms, for reading •

Conversation areas •

Dining •

Kitchen, critical seeing •

Laundry •

Sewing •

SCHOOLS

Assembly

Auditoria •

Social activity •

Classrooms

General •

Lecture demonstration •

Science laboratories •

STORES

Circulation •

Feature displays •

Merchandise displays •

Sales transactions • ***

Wrapping and packaging •

*If #4 pencil or harder leads are used for handwritten tasks.**If tasks involve poor copies, photographs, maps, or 6 point type.

***If handwritten carbon copies.Based on the IESNA Lighting Design Guide, IES Lighting Handbook, 9th Ed. Used with permission from theIlluminating Engineering Society of North America.


268

TABLE 16

DETERMINATION OF ILLUMINANCE CATEGORIES

Orientation and simple visual tasks. Visual performance is largely unimportant. These tasks are found in publicspaces where reading and visual inspection are only occasionally performed. Higher levels are recommended fortasks where visual performance is occasionally important.

A Public spaces 3 fc

B Simple orientation for short visits 5 fc

C Working spaces where simple visual tasks are performed 10 fc

Common visual tasks. Visual performance is important. These tasks are found in commercial, industrial, andresidential applications. Recommended illuminance values differ because of the characteristics of the visual taskbeing lighted. Higher values are recommended for visual tasks with critical elements of low contrast or small size.

D Performance of visual tasks of high contrast and large size 30 fc

E Performance of visual tasks of high contrast and small size, or visual tasks oflow contrast and large size

50 fc

F Performance of visual tasks of low contract and small size 100 fc

Special visual tasks. Visual performance is of critical importance. These tasks are highly specialized, includingthose with very small or very low contrast critical elements. The recommended illuminance values are oftenachieved with supplementary task lighting. The higher recommended values are frequently achieved by moving thelight source closer to the task.

G Performance of the visual task near the threshold 300 to 1,000 fc

Based on the Determination of Illuminance Categories, IES Lighting Handbook, 9th Ed. Used with permission fromthe Illuminating Engineering Society of North America.

269

A P P E N D I X

References

Anderson, Bruce, with Michael Riordan. The SolarHome Book. Andover: Brick House Pub-lishing Co., 1976.

Arnheim, Rudolf. The Dynamics of ArchitecturalForm. Berkeley: University of CaliforniaPress, 1977.

Evans, Benjamin H., AIA. Daylight in Architecture.New York: McGraw-Hill Book Company,1981.

Flynn, John E. “A Study of Subjective Responsesto Low Energy and Nonuniform Lighting Sys-tems.” Lighting Design + Application Febru-ary 1977: 6–14.

——— . “The Psychology of Light.” ElectricalConsultant December 1972–August 1973.Series of 8 articles.

Flynn, John E., and Samuel M. Mills. ArchitecturalLighting Graphics. New York: Reinhold Pub-lishing Corporation, 1962.

Flynn, John E., and Arthur W. Segil. ArchitecturalInterior Systems. New York: Van NostrandReinhold Co., 1970.

Flynn, John E. and Terry J. Spencer. “The Effectsof Light Source Color on User Impression and

Satisfaction.” Journal of the IlluminatingEngineering Society April 1977: 167–179.

Flynn, John E., Terry J. Spencer, Osyp Martyniuk,and Clyde Hendrik. “Interim Study of Proce-dures for Investigating the Effect of Light onImpression and Behavior. Journal of the Illu-minating Engineering Society October 1993:87–94.

Gordon, Gary. “The Design Department.” Archi-tectural Lighting November 1986–May1987. Series of 6 articles.

———. “Specialty Lighting.” Encyclopedia ofArchitecture: Design, Engineering, and Con-struction. New York: John Wiley & Sons,1989.

Graham, Frank D. Audel’s Handy Book of Practi-cal Electricity. New York: Theo. Audel & Co.,1941.

Gregory, Richard L. Eye and Brain. 5th ed. Prince-ton: Princeton University Press, 1997.

Guide to Dimming Low Voltage Lighting.Coopersburg: Lutron Electronics Co., 1989.

Guide to Fluorescent Lamps. Somerset: PhilipsLighting Company, 1988.

271

Guide to High Intensity Discharge Lamps.Somerset: Philips Lighting Company, 1991.

Guide to Incandescent Lamps. Somerset: PhilipsLighting Company, 1986.

Hall, Edward T. The Hidden Dimension. GardenCity: Doubleday, 1966.

High Intensity Discharge Lamps. Cleveland: Gen-eral Electric Company, 1975.

Hurvich, Leo M., and Dorothea Jameson. ThePerception of Brightness and Darkness.Boston: Allyn and Bacon, Inc., 1966.

Incandescent Lamps. Cleveland: General ElectricCompany, 1984.

Kahn, Louis I. Light is the Theme. Fort Worth:Kimbell Art Foundation, 1975.

Lambert, Johann Heinrich. Photometry or On theMeasure and Gradations of Light, Colors andShade. Trans. David L DiLaura. New York:Illuminating Engineering Society of NorthAmerica, 2001.

Lamp and Ballast Product Catalog 2002.Danvers, MA: Osram Sylvania, 2002.

Lamp Products Catalog 2001–2002. Cleveland:General Electric Company, 2001.

Lamp Specification and Application Guide 2001/2002. Somerset: Philips Lighting Company,2001.

Light and Color. Cleveland: General Electric Com-pany, 1978.

Marsteller, John. “A Philosophy of Light: RecallingRichard Kelly’s Three Functional Elements.”Interior Design February 1987: 78–80.

MasterColor Metal Halide Lamps. Somerset:Philips Lighting Company, 1999.

Mehrabian, Albert. Public Spaces and PrivateSpaces. New York: Basic Books Inc., 1976.

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Moore, Fuller. Concepts and Practice of Architec-tural Daylighting. New York: Van NostrandReinhold Company, 1985.

Parker, Bertha Morris. Electricity. Evanston: Row,Peterson and Company, 1944.

Rea, Mark S., ed. Lighting Handbook. 9th ed.New York: Illuminating Engineering Societyof North America, 2000.

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Smith, Robert L. “Lessons in Luminance.”Lighting Design + Application August 1992:10–12.

Tanizaki, Jun’ichiro. In Praise of Shadows. NewHaven: Leete’s Island Books, 1977.

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Credits

COLOR PLATES

1 Courtesy of GE Lighting.2 Courtesy of GE Lighting.3 Courtesy of GE Lighting.4 Courtesy of GE Lighting.5 Gagosian Residence, Francois de Menil Architect. Photo by Paul Warchol.6 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.7 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.8 Gagosian Residence, Francois de Menil Architect. Photo by Paul Warchol.9 Courtesy of GE Lighting.7 Courtesy of GE Lighting.11 Courtesy of GE Lighting.12 Courtesy of GE Lighting.13 Courtesy of GE Lighting.14 Courtesy of Philips Lighting.15 Courtesy of Philips Lighting.16 Courtesy of Philips Lighting.17 Courtesy of Philips Lighting.18 Courtesy of GE Lighting.19 Courtesy of Philips Lighting.20 Courtesy of Philips Lighting.21 Courtesy of Philips Lighting.

273

22 Courtesy of Philips Lighting.23 Courtesy of Philips Lighting.24 Courtesy of Philips Lighting.25 Courtesy of Philips Lighting.26 Courtesy of GE Lighting.27 Courtesy of GE Lighting.28 Courtesy of GE Lighting.29 Courtesy of GE Lighting.30 Courtesy of GE Lighting.31 Courtesy of Philips Lighting.

LUMINAIRE DRAWINGSMany of the drawings in Chapter 12 are based on luminaires originally manufactured by Edison PriceIncorporated. The following illustrations are based on luminaires first designed by Edison Price:Figure 12.7 for the First Unitarian Church, Rochester, 1963.Figure 12.8 for the Hartford Fire Insurance Building, 1961.Figure 12.11 for the CIT Building Headquarters Lobby, 1958.Figure 12.13 for the Philadelphia Academy of Music, 1957.Figure 12.15 for the Knoll Chicago Showroom, 1954.Figure 12.17 the first parabolic, low-brightness, fluorescent downlight was designed for the Upjohn

Executive Headquarters Building, 1961.Figure 12.19 for the Chicago Civic Center, 1965.Figure 12.21 for the Munson-Williams-Proctor Museum, 1960.Figure 12.22 for the Museum of Modern Art, 1958.Figure 12.24 for the Munson-Williams-Proctor Museum, 1960.Figure 12.25 for the Lyndon Baines Johnson Library, 1971.Figure 12.26 for the Lyndon Baines Johnson Library, 1971.Figure 12.28 for 9 West 58 Street, New York City, 1971.Figure 12.31 for the Seagram Building Lobby,1957.Figure 12.47 for the Yale Art Gallery Building, 1953.Figure 12.49 for St. John’s College, 1965.

PHOTOGRAPHSThe lighting for all projects was designed by Gary Gordon LLC except figures 13.9, 13.33, 13.34, and13.35, as noted below.Figure 2.1 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.Figure 2.2 Armenian Evangelical Church, Lee H. Skolnick Architect. Photo by Stan Reiss.Figure 2.3 Offices for Gary Gordon LLC, Donna Selene Seftel Architect.Figure 2.4 One Fifth Avenue Restaurant, Pentagram Architectural Services. Photo by Peter Mauss/

Esto.Figure 2.5 Martinez Valero Shoe Store, Zivkovic Associates. Photo by Ashley Ranson.Figure 2.6 City Bakery, Turett Collaborative Architects. Photo by Paul Warchol.Figure 2.7 Australia Broadcasting Corporation, Zivkovic Associates Architects. Photo by Ashley

Ranson.

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Figure 2.8 Private Residence, Frank and Marcotullio Design Associates. Photo by Michael Gordon.Figure 2.15 Club Monaco, Deborah Berke Architect. Photo by Catherine Bogert.Figure 2.16 Marketplace at Newport, Turett Collaborative Architects. Photo by Paul Warchol.Figure 2.17 One Fifth Avenue Restaurant, Pentagram Architectural Services. Photo by Peter Mauss/

Esto.Figure 2.18 Tommy Boy Records, Turett Collaborative Architects. Photo by Paul Warchol.Figure 3.3 Private residence, Sidnam|Petrone Architect. Photo by Peter L. Goodman.Figure 3.5 Armenian Evangelical Church, Lee H. Skolnick Architect. Photo by Stan Reiss.Figure 3.7 Lillian Vernon Residence, Hardy Holzman Pfeiffer Associates. Photo by Gideon Louis.Figure 3.8 Sedona Store, Andaloro Associates. Photo by George Mott.Figure 3.10 Morton Productions, BumpZoid. Photo by Langdon Clay.Figure 3.12 Armenian Evangelical Church, Lee H. Skolnick Architect. Photo by Stan Reiss.Figure 3.14 Yale University School of Art, Deborah Berke Architect. Photo by Catherine Bogert.Figure 3.16 Offices for Omon Ltd., Zivkovic Associates Architects. Photo by Ashley Ranson.Figure 3.17 Lillian Vernon Residence, Hardy Holzman Pfeiffer Associates. Photo by Gideon Louis.Figure 3.18 Gagosian Residence, Francois de Menil Architect. Photo by Paul Warchol.Figure 3.19 Yale University School of Art, Deborah Berke Architect. Photo by Catherine BogertFigure 3.20 City Bakery, Turett Collaborative Architects. Photo by Paul Warchol.Figure 3.22 Photo by Photosphere.Figure 3.24 Photo by Photosphere.Figure 3.25 Photo by Photosphere.Figure 3.26 Photo by Photosphere.Figure 3.27 Photo courtesy of GE Lighting.Figure 3.28 Photo courtesy of GE Lighting.Figure 12.57 The New Gotham Lobby, Stephen Alton Architects. Photo by Eduard Hueber.Figure 12.58 Armenian Evangelical Church, Lee H. Skolnick Architect. Photo by Stan Reiss.Figure 12.59 Neuman and Bogdanoff, Pentagram Architectural Services. Photo by Peter Mauss/Esto.Figure 12.60 Findler Residence, Bruce Bierman Design. Photo by Andrew Bardwin.Figure 12.61 The New Gotham Lobby, Stephen Alton Architects. Photo by Eduard Hueber.Figure 13.1 Offices for Gary Gordon LLC, Donna Selene Seftel Architect.Figure 13.2 Club Monaco, Deborah Berke Architect. Photo by Catherine Bogert.Figure 13.3 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.Figure 13.7 Gagosian Residence, Francois de Menil Architect. Photo by Paul Warchol.Figure 13.8 Residence for Adam R. Rose and Peter R. McQuillan, Stuart Mager Incorporated. Photo by

David Mager.Figure 13.9 Photo courtesy of Halo Lighting.Figure 13.11 Findler Residence, Bruce Bierman Design. Photo by Andrew Bardwin.Figure 13.22 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.Figure 13.27 Gagosian Residence, Francois de Menil Architect. Photo by Paul Warchol.Figure 13.28 Lillian Vernon Residence, Hardy Holzman Pfeiffer Associates. Photo by Gideon Louis.Figure 13.29 Martinez Valero Shoe Store, Zivkovic Associates. Photo by Ashley Ranson.Figure 13.30 Club Monaco, Deborah Berke Architect. Photo by Catherine Bogert.Figure 13.31 Martinez Valero Shoe Store, Zivkovic Associates. Photo by Ashley Ranson.Figure 13.32 St. Mark’s Bookshop, Zivkovic Associates Architects. Photo by Ashley Ranson.

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C R E D I T S

Figure 13.33 Four Seasons Restaurant, Philip Johnson Architect. Lighting design by Richard Kelly.Photo courtesy of GE Lighting.



Figure 13.37 Club Monaco, Deborah Berke Architect. Photo by Catherine Bogert.Figure 13.38 The New Gotham Lobby, Stephen Alton Architects. Photo by Eduard Hueber.Figure 13.39 Tommy Boy Records, Turett Collaborative Architects. Photo by Paul Warchol.Figure 13.40 Tommy Boy Records, Turett Collaborative Architects. Photo by Paul Warchol.Figure 13.41 The New Gotham Lobby, Stephen Alton Architects. Photo by Eduard Hueber.Figure 13.42 Club Monaco, Deborah Berke Architect. Photo by Catherine Bogert.Figure 13.43 St. Mark’s Bookshop, Zivkovic Associates Architects. Photo by Ashley Ranson.Figure 13.44 Prudential Insurance Company of America, Grad Associates. Photo by Peter L. Goodman.Figure 13.45 Marketplace at Newport, Turett Collaborative Architects. Photo by Paul Warchol.

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Glossary

“Accent” light: an advertising term misapplied toadjustable, directional luminaires that areproperly termed object lights. See object light.

Accommodation: the automatic adjustment ofthe eye for seeing at varied distances,accomplished by changes in focus.

Acuity (also called visual acuity): the ability ofthe eye to make out fine detail.

Adaptation: the change in the sensitivity of thevisual system based on the amount of lightthe retina has been exposed to in the recentpast. Dark adaptation is an increase in visualsensitivity that occurs over time in darkness.

Ambient light: general or background illumina-tion.

Ampere: measurement of the rate of flow of anelectric current; it is equivalent to the steadycurrent produced by one volt applied acrossa resistance of one ohm.

Anodize: to coat a metal (usually aluminum) witha protective film by subjecting it to electro-lytic action.

Aperture (of a luminaire): the diameter of theopening of a recessed luminaire.

Apparent color temperature: See correlatedcolor temperature.

Axial (filament): a filament situated in the direc-tion of the lamp axis.

Baffle: a single opaque or translucent element toshield glare at normal viewing angles in onedirection, along a single axis. For small-aper-ture luminaires, a baffle around the perime-ter provides shielding from all directions. Seealso louvers.

Ballast: an auxiliary device for an electric dis-charge source that provides the proper start-ing voltage and regulates the lamp operatingcurrent. All fluorescent and HID lampsrequire a ballast for proper operation.

Ballast factor: the ratio of light output producedby lamps operated by a commercially-avail-able ballast to light output produced by lampspowered by a laboratory-reference ballast.

Beam angle: the angle between the two direc-tions for which the intensity is 50% of themaximum, as measured in a plane throughthe beam centerline. See also field angle.

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Beam-spread: the angular cone of light createdby the distribution of the lamp or luminaire,in the plane of the beam axis. See also beamangle and field angle.

Borosilicate: a silicate glass containing oxide ofboron that has high heat-resistance.

Brightness: a subjective experience that occursin the consciousness of a human observer, aresult of the intensity of light falling on agiven region of the retina at a certain time,the intensity of light that the retina has beensubject to in the recent past, and the intensi-ties of light falling on other regions of theretina. See also luminance.

Bulb: the outer hard, soft, or quartz glass enve-lope of an electric lamp, which may contain avacuum, elemental inert gas, or metal, and ameans of light generation. Also, the lay-man’s term for an electric lamp.

Candela (cd): the unit of luminous intensityemitted in a specific direction by a source,equal to one lumen per steradian.

Candlepower: a vernacular term for luminousintensity expressed in candelas.

Candlepower distribution curve: properly calleda luminous intensity distribution curve, itdepicts the amount of luminous intensity(expressed in candelas) generated in eachdirection by a light source in a plane throughthe center of the source.

Capacitive: the part of an electric circuit thatexhibits the ability to store charge.

Capacitor: an electric circuit element included insome magnetic ballasts that consists of twometallic plates, separated and insulatedfrom each other, used for storing chargetemporarily.

Cathode: one of two electron-emitting elec-trodes hermetically sealed into a fluorescentlamp, consisting of metal cylinders (coldcathode) or coiled tungsten wire (hot cath-ode), and usually coated with an electron-emissive material.

Clerestory: a window located in the upper por-tion of a wall that admits natural light into thecenter of a room.

Coefficient of utilization: the ratio of thenumber of lumens expected to reach thework plane divided by the number of lumensgenerated by the bare lamps of a specificluminaire in a specific room.

Color constancy: knowledge of the normal colorof objects. We tend to see surface andobject colors as the same despite changesto the color of light illuminating the surfaceor object.

Color rendering index (CRI): the comparisonbetween the color-rendering ability of a givenlight source and a reference light source,expressed as an Ra factor on a scale of 1 to100.

Color rendition: how surface and object colorsappear under a given light source, in com-parison with their color appearance under areference light source.

Color spectrum: the continuum of color formedwhen a beam of white light is dispersed (asby a prism) so that its component wave-lengths are arranged in order.

Color temperature: the color appearance of thelight that emanates from a source, mea-sured in Kelvin (K). Not a measure of the sur-face temperature of a lamp, it is the absolutetemperature of a laboratory blackbody radia-tor when its visible radiation matches thecolor of the light source.

Contrast: the relationship between the intensi-ties of an object and its surrounding areas;the degree of difference between light anddark. See also luminance contrast.

Correlated color temperature (CCT): the colorappearance of the light that emanates froman electric light source with a discontinuousspectrum, measured in Kelvin (K).

Cove: a concave or canted interior corner ormolding, especially at the transition fromwall to ceiling; sometimes used to shieldlight sources that distribute light across theceiling plane.

Current: the flow of electricity in a circuit; the rateof flow of an electric current is measured inamperes (amps, A).

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Cutoff: measured up from nadir, the angle of thefirst line of sight at which the bare lightsource is not visible.

Daylighting: the illumination of indoor spaces bynatural light.

Dichroic: the property of transmitting certainwavelengths of light while reflecting thosenot transmitted, usually with little absorp-tion.

Diffraction grating: a glass or polished metalsurface that has a large number of very fineparallel grooves or slits, used to change thedirections and intensities of a group of wave-lengths of reflected or transmitted light.

Diffuse light: a distribution of light that is dis-persed in a wide pattern and not incidentfrom any particular direction.

Diffuser: a glass or plastic material that dis-perses light from a source in all directions,eliminating the directional quality of thebeam; in fluorescent downlights, used toredirect light from the glare zone downtoward work surfaces.

Dimmer: a device that provides variation in theintensity of a luminaire by controlling thevoltage or current available.

Direct glare: excessive light misdirected towardthe eye. It refers to glare from the direct viewof luminaries or bare lamps. See alsoreflected glare.

Direct/indirect: light emitted in a downward andupward direction, with little or no light emit-ted at angles near the horizontal.

Direct (light): a distribution of light emitted in adownward direction.

Downlight: a recessed, surface-mounted, orpendant-mounted luminaire which emitslight in a downward direction with no upwardcomponent of light.

Downlighting: a distribution of light emitted in adownward direction.

Discharge source: a lamp that produces light bythe passage of an electric current through avapor or gas, rather than through a tungstenwire as in incandescent lamps. (Theseinclude cold-cathode, fluorescent, high-

pressure sodium, low-pressure sodium, mer-cury vapor, metal halide, and neon lamps.)

Efficacy: the ratio of lumens produced to elec-tricity consumed when referring to a lightsource, expressed in lumens per watt.

Efficiency: the ratio of lumens emitted by aluminaire to that emitted by the lamp(s) con-tained within it, expressed as a percentage.

Ellipsoidal: in the shape of an ellipse, which hastwo focal points. In a reflecting contour, a rayof light originating at one focal point isreflected through the second focus.

Emissive material: in electric lamps, a sub-stance that discharges electrons, usuallyapplied as a coating to the cathode of a dis-charge source.

Energy-effective: when referring to electriclighting, using the available watts to supplylight where it is needed and when it isneeded, and limit light from where it isunwanted.

Exitance: the total quantity of light emitted,reflected, or transmitted in all directionsfrom a surface. Properly defined as density offlux leaving a surface, it is measured inlumens per square foot (lm/ft2) or lumens persquare meter (lm/m2).

Fenestration: The arrangement, proportioning,and design of windows and doors in a build-ing for the admission of daylight.

Fiber optics: thin, flexible fibers of glass or plas-tic that are enclosed by a material of a lowerindex of refraction, transmitting lightthroughout their length by internal reflection.

Field angle: the angle between the two direc-tions for which the intensity is 10% of themaximum, as measured in a plane throughthe beam centerline. See also beam angle.

Filament: the fine tungsten wire in an electriclamp, which acts as a conductor andbecomes incandescent by the passage of anelectric current.

Filter: a transparent material that modifies thecolor or quantity of light by transmission orreflection.

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G L O S S A R Y

“Fixture”: layman’s term for a luminaire. Seeluminaire.

“Floor lamp”: layman’s term for a torchère. Seetorchère.

Fluoresce: the emission of visible light caused bythe absorption of radiation of shorter wave-lengths followed by a nearly immediate re-radiation at a longer wavelength.

Fluorescent lamp: a low-pressure, mercury-vapor, electric-discharge lamp having aphosphor coating on its inner surface thattransforms the ultraviolet energy generatedby the discharge into visible light.

Flux: see luminous flux.

Focused light or focal glow: concentrated lightof greater intensity on a particular area orobject, compared to its backgroundilluminance, intentionally establishing a hier-archy between foreground and background.

Footcandle (fc): the unit measurement ofilluminance equal to one lumen per squarefoot, originally defined with reference to astandardized candle burning at one foot froma given surface.

Footlambert (fL): unit measurement of reflectedlight from a perfectly diffusing surface thatemits or reflects one lumen per square foot;equal to 1/π candela per square foot; nowdeprecated.

Fresnel (pronounced fra-nel/) lens: a thin, opti-cal lens that consists of a series of concen-tric lens sections regressed into a planararray; in luminaires, it produces a concen-trated beam of light while also reducing thebrightness of the source.

General diffuse: a multidirectional lighting distri-bution produced by luminaires that deliverboth upward and downward components oflight.

Glare: the sensation produced by an extremeluminance within the normal field of viewthat is sufficiently greater than the lumi-nance to which the eyes are adapted.

High-bay lighting: interior lighting where mount-ing height is greater than approximately 25 ftabove the floor.

High contrast: a lighting condition characterizedby a large proportion of focused light (on anobject or the foreground) and a smallamount of diffuse light (the background).

High load: an elevated degree of psychologicalstimulation or arousal, caused by activitiesor environments that are complex, crowded,asymmetrical, novel, unfamiliar, surprising,or random.

High-pressure sodium: a high-intensity dis-charge lamp in which light is produced byradiation from the combined vapors of mer-cury and sodium, with the latter dominatingthe yellow-amber color.

Hue: spectral color; light of a specific wavelength.

Hydroform: a method of machine-forming metalthat consists of a draw ring, flexible die,punch, and a pressurized forming cavity. (Inluminaires, it is used to form reflectors fromaluminum.)

Illuminance: the density of light received at apoint on a surface. Properly defined as den-sity of flux incident on a surface measuredperpendicular to the surface, it is measuredin footcandles (fc).

Incandescence: the emission of light from anobject as a result of its being heated.

Incandescent lamp: an electric lamp in which afilament produces light when heated toincandescence by an electric current.

Incident: light rays falling upon or striking a sur-face.

Included angle: formed between or within twointersecting straight lines.

Indirect: an upward distribution of light whichproduces illumination on the horizontalworkplane via reflection from the ceiling andupper walls.

Inductive: the property of an electric circuit inwhich an electromagnetic charge is inducedin it as the result of a changing magnetic flux.

Infrared: wavelengths in the region of the elec-tromagnetic spectrum immediately abovethe visible spectrum, from 770 to 106 nm.

Intensity: the physical energy of light emitted in aspecific direction by a source. Properly called

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luminous intensity and defined as flux persolid angle in a given direction, it is mea-sured in candelas (cd).

Interreflection: the multiple reflection of light bythe various room surfaces before it reachesthe workplane.

Iodide: a salt of hydriodic acid, a compound ofiodine; used in metal halide lamps.

Ionize: to convert into ions; a group of atoms thatcarry a positive or negative electrical chargeas a result of having lost or gained one ormore electrons.

Isofootcandle plot: a computer-generated dia-gram on the Cartesian coordinate systemshowing contour lines of varying illuminancevalues from a specific luminaire in a specificapplication; a shaded plan with gray scalesrepresenting the range of illuminancevalues.

Kelvin: the unit of absolute temperature used todesignate the color temperature of a lightsource.

Kilowatt: a unit of power equal to 1,000 watts.

Lamp: a source that converts electricity into light;it is the technical word for what is commonlyreferred to as a “light bulb.”

Lampholder: the component of a luminaire thataccepts the lamp base and supplies it withelectricity; it is the technical word for what iscommonly referred to as a “socket.”

Laser: acronym for light amplification by stimu-lated emission of radiation; most lasers areoscillators (generators or sources of light)not amplifiers, producing a monochromaticbeam of radiation by steady oscillation main-tained in a resonator.

LED: acronym for light-emitting diode; a semi-conductor diode that emits light when volt-age is applied to it.

Lens: a glass or plastic element used inluminaires to control the direction and distri-bution of transmitted light by refraction.

Light: a narrow band of electromagnetic energy,ranging from approximately 380 nanometers(nm) to 760 nm, which stimulates receptorsin the eye that enable vision.

Lime glass: glass with a high calcium oxide con-tent consisting of silica, alumina, and ironthat has greenish hue.

Louver: a series of baffles or shielding elementsused to shield glare at normal viewingangles, usually arranged in a geometric pat-tern to provide shielding from many direc-tions with minimum interference to thedesired beam distribution.

Low contrast: a lighting condition characterizedby a large proportion of diffuse light and asmall amount of focused light.

Low load: a small amount of psychological stim-ulation or arousal, resulting from activities orenvironments that are simple, uncrowded,symmetrical, conventional, familiar, unsur-prising, or organized.

Low-pressure sodium: a discharge lamp inwhich light is produced by radiation fromsodium vapor, with a monochromatic yellowcolor.

Lumen (lm): the unit measurement of luminousflux equal to the light emitted in a solid angleby a uniform point source of one candelaintensity.

Luminaire: a complete lighting unit consisting ofa housing; lamp(s); light controlling ele-ments; brightness controlling element;lampholder(s); auxiliary equipment, such asballast or transformer, if required; and a con-nection to the power supply.

Luminance: the objective measurement of inten-sity of light entering the eye, per unit of pro-jected area. It is the accepted term for lightthat is reflected from a surface in a givendirection (back towards the eyes). Properlydefined as intensity of flux leaving a surfacein a given direction, it is measured in cande-las per square foot (cd/ft2) or candelas persquare meter (cd/m2).

Luminance contrast: the ratio of the luminanceof an object or the foreground to the lumi-nance of its immediate background or sur-round.

Luminous: emitting or reflecting energy in thevisible portion of the electromagnetic spec-trum.

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G L O S S A R Y

Luminous flux: light emitted in all directions by asource. Properly defined as time rate flow oflight, it is measured in lumens (lm).

Matte: a dull finish or surface lacking in luster,gloss, shine, or highlights.

Mercury lamp (properly called a mercury vaporlamp): a high-intensity discharge lamp inwhich light is produced by an electric dis-charge through mercury vapor.

Metal halide: a high-intensity discharge lamp inwhich light is produced by an electric dis-charge through the combined vapors of mer-cury and metal halides, which are introducedinto the arc tube as compound iodides.

milliAmpere: a unit of electric current equal toone thousandth of an ampere.

Monochromatic: having or consisting of only onecolor or hue, or radiation of a single wave-length or very small range of wavelengths.

Motion sensor: see occupancy sensor.Nadir: straight down (0-degree angle).Nanometer: a unit of wavelength equal to one

billionth (10-9) of a meter.Object light: an adjustable, directional luminaire

that provides an asymmetric distribution oflight aimed at one or several objects. Alsocalled “spot lights,” they are used to providefocal glow and add contrast to a setting.

Occupancy sensor: a device that provides on-offcontrol of luminaires in response to the pres-ence or absence of occupants in a space,sensed by audio, ultrasonic, passive infra-red, or optical means.

Ohm: the standard unit of electrical resistance ofa conductor, such that a current of oneampere in its circuit produces a decrease involtage across it of one volt.

Opaque: blocking the passage of light; neithertransparent nor translucent.

Parabolic: having the form of a parabola, a planecurve generated by the intersection of thesurface of a cone with a plane parallel to oneof its sides.

Pendant (luminaire): a luminaire that is sus-pended from the ceiling by a support cable,chain, cord, rod, or stem.

Phosphor: a chemical substance that convertsinvisible ultraviolet radiation into visible light.

Photometer: an instrument for measuring lumi-nous intensity, luminous flux, illuminance, orluminance.

Photometry: the science that measures light.

Photosensor: a light-sensing device used tocontrol luminaires and dimmers in responseto detected illuminance values.

Photopic: vision, using the cones of the retina,under relatively high illuminance values.

Prism: a transparent body with three rectangularplane faces, or sides, and two equal and par-allel triangular ends or bases, used to refractor disperse a beam of light.

Quad-phosphor: a combination of four narrowspectra, rare-earth phosphors used in fluo-rescent lamps to produce a wide-rangespectrum of visible light. The individual phos-phors correspond to the short-, middle-, andlong-wavelength regions of the visible spec-trum.

Reflected glare: excessive uncontrolled lumi-nance reflected from objects or surfaces inthe field of view.

Reflection: the return of light from a surface.Specular reflection occurs when the surfacealters the direction of a beam of light withoutchanging its form; the angle of reflection isequal to the angle of incidence. Spreadreflection partially disperses this reflectedbeam. Diffuse reflection occurs when an inci-dent ray of light is reflected in all directions.

Refraction: the deflection of a light ray when itpasses obliquely from one medium (such asair) into another (such as water) in which ittravels at a different speed.

Relamp: to replace a lamp or lamps.

Restrike: after a high-intensity discharge lamp isextinguished, it must cool sufficiently toreduce the vapor pressure to a point wherethe arc can be reignited.

Scotopic: vision, using the rods of the retina,under relatively dim light.

Semi-specular: an irregular surface that partiallydisperses or spreads the reflected beam,

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with the greatest intensity of light reflected atan angle near the angle of incidence.

Shielding angle: the zone within which shielding(baffles or louvers) conceals the light sourceand controls glare.

Sight line: the line extending from an observer’seye to the point at which a bare light sourcefirst becomes visible.

Skylight: 1. the diffused and reflected light of thesky; it is light from the sun redirected by theatmosphere. 2. an opening in the roof of abuilding, glazed with a transparent or trans-lucent material, that is designed to admitnatural light.

Slimline: a linear fluorescent lamp with a single-pin base that is capable of being operated atmore than one current and wattage.

Soffit: the exposed underside of any overheadcomponent of a building, such as an arch,balcony, beam, cornice, lintel, or vault.

Spacing criterion (SC) or spacing-to-mount-ing-height ratio (S/MH): an estimated max-imum ratio of luminaire spacing to luminairemounting height above the workplane, nec-essary to achieve uniform, horizontalilluminance.

Spectral: of, relating to, or made by the colorspectrum or electromagnetic spectrum.

Specular: having the reflecting properties of amirror; a smooth reflecting surface. Theangle of reflection is equal to the angle ofincidence.

Splice: the electrical connection of luminairewires to the building branch circuit wires.

Stroboscopic: when rapidly moving objects areobserved under discharge sources, blurred“ghost” images are sometimes observedthat cause the objects to appear slowed,stopped, or moving in reverse.

Torchère: a portable luminaire suitable for stand-ing on the floor, which directs most, or all, ofits light upward.

Toroidal: doughnut-shaped.

Total internal reflection: occurs when lightpasses into a transparent medium, such asglass or plastic, at an appropriate angle so

that it travels inside the medium repeatedlyreflecting from side to side.

Transformer: a device with two or more coupledwindings, used to convert the supply of elec-tric power at one voltage in a primary circuitto a lower voltage in a secondary circuit.

Translucent: having the property of transmittingdiffused light but obscuring vision, so thatobjects beyond cannot be seen clearly.

Transmission: the passage of light throughspace or a medium; it is altered by the reflec-tions at each surface of the medium, and bythe absorption and reflection within themedium.

Transparent: having the property of transmittinglight without altering its distribution, so thatobjects beyond are seen clearly.

Triphosphor: a combination of three narrowspectra, rare-earth phosphors used in fluo-rescent lamps to produce a wide-rangespectrum of visible light. The individual phos-phors correspond to the peak spectral sensi-tivities of human vision: blue-violet, puregreen, and orange-red.

“Troffer”: layman’s term for a recessed, rectilin-ear fluorescent downlight; perhaps derivedfrom “trough” and “coffer.”

Trough: a long, narrow opening, usually in theceiling plane; sometimes called a slot.

Tungsten-halogen: an incandescent lamp with aselected gas of the halogen family sealedinto it to stop evaporated tungsten fromdepositing on the bulb wall.

Ultraviolet (UV): radiant energy having a wave-length shorter than wavelengths of visiblelight and longer than those of x-rays; withinthe range of 10 nanometers (nm) to 380nm.

Uplight: a luminaire that emits light in an upwarddirection toward the ceiling, with no down-ward component of light.

Uplighting: a distribution of light emitted in anupward direction.

Valance: a longitudinal shielding panel mountedover a window with draperies to conceal light

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G L O S S A R Y

sources that provide both uplight anddownlight.

Veiling reflection: a reflection of incident lightthat partially or completely obscures thedetails on a surface by reducing its contrast.See also reflected glare.

Visual comfort: the degree of visual satisfactionproduced by the luminous environment,resulting from the reduction of glare and dis-tracting luminance in the field of view.

Visible spectrum: wavelengths of electromag-netic energy, ranging from approximately380 nanometers (nm) to 760 nm.

Volt: the standard unit of measurement for elec-trical potential; when applied across a resis-tance of one ohm, it will result in a currentflow of one ampere.

Wall-washer: a luminaire with an asymmetricdistribution used for illuminating vertical sur-faces from ceiling to floor without noticeablevariation in intensity.

Watt: the unit of electrical power; it is equal tothe power produced by a current of oneampere across a potential difference of onevolt.

Wattage: the amount of power expressed inwatts.

Wavelength: the distance between one peak orcrest of a wave of light, heat, or other energy,and the next corresponding peak or crest.

Workplane: the plane on which visual tasks areusually done; a horizontal plane 2 ft 6 in.above the floor, unless otherwise indicated.

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Index

AAdaptation, brightness, 8Age level, recommended illuminance values, 125–

126Air-conditioning load, ballast systems, 103Alternating current, electrical circuits, 136Aluminum, reflector materials, 109Aluminum reflector (AR) lamp, 76Ambient light:

design, 220–224light elements, 14, 16, 17–18

American National Standards Institute (ANSI), 94Amperes, electricity, 135Aperture, recessed housings, 149Aperture lamps, fluorescent lamps, 87–88Architectural coves, ceiling plane wash lights, 184–

186, 187, 190–193Architectural surfaces, lighting design, 213–218Architecture/light integration, design, 240–242Artwork, lighting design, 224–229Astigmatic vision, 5Asymmetric wash lights, 169–178

downlight/wall-washer, 169–171reflector wall-washers, 171–178

Autotransformer dimmers, 142Auxiliary equipment, 99–104

ballast systems, 100–104transformers, 99–100

Awnings, shading devices, 58, 59

BBaffles, glare control, 116, 118–119Balance of brightness, design, 229–237. See also

BrightnessBallast systems, 100–104

air-conditioning load, 103efficiency, 102–103electromagnetic, 101

electronic, 103energy-saving, 104fluorescent dimming ballasts, 103–104fluorescent heater-cutout ballasts, 104fluorescent lamps, 83–86generally, 100–101high-intensity discharge (HID) lamps, 96power factor, 101–102

Bases, incandescent lamps, 64, 67Beam-spread, luminaires, 25Black light fluorescent lamps, 92Brain:

color perception, 9–10perception, 6

Branch circuit, electric distribution, 138Brightness, 25–42. See also Contrast

color, 9degrees of, 12–14design, balance, 229–237direction and distribution of light, 25–31emotional impact, 11glare, 35–41luminance compared, 25perception, 6, 8photometrics, 122–123relative brightness for equal attraction, table, 259sparkle, 41–42subjective impressions, 18surface finishes and reflectance, 31three-dimensional form, 31, 33–35

Brilliants, sparkle, 16–17BX, electrical wiring, 136

CCartesian graph, luminous intensity distribution curve,

123–124Ceiling plane, wash lights, 182–193Central lighting control systems, 146–148

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Ceramic metal halide lamps:color, 49–50described, 94

Circuit(s), electricity, 135, 136–137Circuit breaker, electrical circuits, 137Circular contour reflector, described, 107–108Clerestories, daylight design, 54–55Coefficient of utilization (CU):

illuminance calculations, 130–131table of, 266

Cold-cathode fluorescent lamp, 81–82Color, 43–50

brightness, 31, 32daylight, 51light, 4light sources, 46–50

fluorescent, 48–49high-intensity discharge (HID) light, 49–50, 94incandescent, 47–48

perception, 9–10rendering, 45–46spectral distribution, 43–45subjective impressions, 46temperature, 45

Color constancy, defined, 10Colored light:

fluorescent lamps, 92incandescent lamps, 77–80relative output table, 258

Color Rendering Index (CRI), 45–46, 244–245Color vision, eye, 5Compact fluorescent lamps, 88–91Complete circuit, electricity, 135Compound contour reflector, described, 107–108Computer assistance, illuminance calculations, 132–

133. See also Video display terminals (VDTs)Concave lens, refraction, 113, 115Concentrated distribution, light, 25, 26–27, 28Conductors, electrical wiring, 136Cones, eye, 5, 8, 9Conservation of materials, artwork lighting design,

227–229Contours, reflection, 106–108. See also ReflectionContrast. See also Brightness

brightness, 8emotional impact, 11

Control station, central lighting control systems, 146–148

Convex lens, refraction, 113, 114–115Correlated color temperature, 45Costs, life cycle, electricity, 138–139. See also

Energy efficiencyCoves. See Architectural covesCross-baffles, object lights, 197Cube-cell louvers, object lights, 197

Current, electric, 135Cutoff angle:

luminaires, 26vertical surface illumination, 216

DDaylight, 51–62

artwork lighting design, 227–229design for, 52–56energy control, 62glazing materials, 60overview, 51–52quantity, 60, 62shading devices, 56–60, 61

Debuzzing coil, dimming control, 144Decorative multidirectional luminaires, 202, 204–208Deep-cell open parabolic louvers, rectilinear

fluorescent downlights, 168Degrees of stimulation, psychology, 11–12Design, 209–241

ambient lighting, 220–224architectural surfaces, 213–218architecture/light integration, 239–241artwork, 224–229balance of brightness, 229–237energy-effective, 237–240integration in, 209task lights, 218–220visual clarity, 209–213

Diffuse light:distribution, 25–26, 27, 29low-contrast environment, 12three-dimensional form, 34

Diffuse reflection, described, 105–106Diffuse reflector, described, 109, 110Diffuse transmission, light control, 111Dimming control and systems, 141–146

autotransformer dimmers, 142daylight energy control, 62fluorescent dimming ballasts, 103–104fluorescent lamps, 145–146high-intensity discharge (HID) lamps, 97, 146incandescent lamps, 143–145resistance dimmers, 141–142solid-state dimmers, 142square law dimming curve, 143

Direct current, electrical circuits, 136Direct distribution, light, 25Direct glare, described, 36–38Direct/indirect luminaires, 27, 30Direct-indirect multidirectional luminaires, 198, 202Directional incandescent lamps, 71–72Directional-source downlights, point source

downlights, 158–159, 164

286


Direct light, three-dimensional form, 34Direct sparkle, described, 41Direct transmission, light control, 109, 111Discharge lamps, 81–98. See also Fluorescent lamps;

High-intensity discharge (HID) lampsfluorescent lamps, 81–92high-intensity discharge (HID) lamps, 45, 49–50,

92–97low-pressure sodium (LPS) lamps, 97–98

Double-pole, single-throw switch, 140Downlights, 154–169

ambient light design, 220–221, 224brightness, 25–26, 27luminous ceilings, 168–169point source, 154–166rectilinear fluorescent downlights, 166–168spacing criterion, 168

Downlight/wall-washer, asymmetric wash lights, 169–171

EEfficiency, ballast systems, 102–103, 104Egg-crate louvers, rectilinear fluorescent downlights,

168Elderly, recommended illuminance values, 125–126Electricity, 135–148

central lighting control systems, 146–148circuits, 136–137dimming control, 141–146

autotransformer dimmers, 142fluorescent lamps, 145–146high-intensity discharge (HID) lamps, 146incandescent lamps, 143–145resistance dimmers, 141–142solid-state dimmers, 142square law dimming curve, 143

distribution, 138life cycle costs, 138–139physics of, 135–136power consumption, 138switch control, 139–141

manual, 139–140occupancy sensors, 140photosensors, 140–141timers, 140wireless remote, 141

wire size and length recommendations, table, 260wiring, 136

Electromagnetic ballast systems, 101Electromagnetic radiation, visible light, 3–4Electronic ballast systems, 103Electronic transformers, described, 100Ellipsoidal downlights, point source downlights, 154,

158, 161

Elliptical contour reflector, described, 107Emotional impact, light, 11EMT conduit, electrical wiring, 136Energy efficiency:

ballast systems, 102–103, 104daylight, 62design, 237–239energy management controls, 147–148fluorescent lamps, 87photosensor switch control, 140power consumption, 138

Energy Policy Act of 1992 (EPACT):fluorescent lamps, 91–92incandescent lamps, 72–73

Exitance, photometrics, 121, 122Extended service, incandescent lamps, 69Eye:

age level, recommended illuminance values, 125–126

brightness, 8perception, 4–6photometrics, 123

Eyeglasses, 5

FFeeder circuit, electric distribution, 138Fenestration. See Daylight; WindowsFiber optics, total internal reflection, 115, 118Filaments, incandescent lamps, 64, 68Filters, colored incandescent lamps, 78Five-way switch, 140Fixed controls, shading devices, 58–60, 61Flicker, fluorescent lamps, 92Fluorescent lamps, 81–92

asymmetric wash lights, 176, 178–179cold-cathode, 81–82color, 45, 46, 48–49colored lamps, 92compact, 88–91comparative luminance table, 256–257designations and properties, table, 254dimming ballasts, 103–104dimming control, 145–146Energy Policy Act of 1992 (EPACT), 91–92flicker, 92heater-cutout ballasts, 104hot-cathode, 82–83lamp-ballast circuits, 83–86lamp life, 91light output, 91linear wash lights, 179–180, 182operation, 81rare-earth phosphores, 86–87rectilinear fluorescent downlights, 166–168

287

I N D E X

Fluorescent lamps (continued)stroboscopic effect, 92variations of, 87–88

Flux, photometrics, 121Flynn, John, 18, 23, 46Focal glow, light elements, 14, 16, 17, 18. See also

Task lightsFocused light, low-contrast environment, 12Footcandle values. See PhotometricsFour-way switch, 140Fresnel lens, refraction, 113, 114, 115Fuse, electrical circuits, 137

GGlare. See also Luminaire(s)

brightness, 35–41control of, 118–120upward light, 27

Glazing materials, windows, 60Glitter. See SparkleGrazing light:

linear wash lights, 180texture, 33–34

Greenfield conduit, electrical wiring, 136

HHalogen infrared (IR) lamp, 75. See also Tungsten-

halogen lampsHeat gain, daylight design, 56Hertz unit, electrical circuits, 136High brackets, multidirectional luminaires, 202, 203High-contrast environment, 14, 15High-intensity discharge (HID) lamps, 92–97

bulb shapes, 94–96color, 45, 46, 49–50dimming, 97dimming control, 146lamp life, 97light output, 97operation, 96types of, 92–94

High-load degree of stimulation, 11–12High-output (HO) lamps, fluorescent lamps, 87High-pressure sodium (HPS) lamps, high-intensity

discharge (HID) light, 49, 93, 94Hot-cathode fluorescent lamp, 82–83Housings, luminaires, 149–154Hue:

color perception, 9defined, 4

Hyperopic vision, 5

IIlluminance:

calculations of, photometrics, 126–133photometrics, 121, 123recommended values, photometrics, 124–126

Illuminance categories, determination of, table, 269Illuminance values:

age level recommendation, 125–126photometric recommendation, 124–126table of recommended, 267–268

Illuminating Engineering Society of North America(IESNA), 122, 125–126

Illusion, perception, 6, 7Incandescent lamps, 63–80

bases of, 64, 67color, 45, 47–48colored light, 77–80comparative luminance table, 256–257designations and properties, table, 246–253dimming control, 143–145Energy Policy Act of 1992 (EPACT), 72–73filaments, 64, 68lamp efficacy and life, 68light output, 68–69linear wash lights, 179low-voltage lamps, 75–77tungsten-halogen lamps, 73–75types of, 63–64, 65–66, 69–73

directional, 71–72nondirectional, 69, 70, 71semi-directional, 69, 71

Infrared light, halogen infrared (IR) lamp, 75. See alsoTungsten-halogen lamps

Infrared present wireless remote switch control, 141Instant-start ballast circuits, fluorescent lamps, 84–85Insulators, electrical wiring, 136Integration, in design, 209Intensity, photometrics, 121Inverse-square method, illuminance calculations,

126–129Iris, eye, 5

JJunction box:

pendant-mounted housings, 154, 155recessed housings, 149, 150semi-recessed housings, 151surface-mounted housings, 149, 152, 153

KKelly, Richard, 14, 16Kerosene lamps, subjective impressions, 46

LLambert, Johann Heinrich, 123Lambertian surfaces, photometrics, 122–123

288


Lamp-ballast circuits, fluorescent lamps, 83–86. Seealso Ballast systems

Lamp efficacy, summary table, 255Lamp life:

fluorescent lamps, 91high-intensity discharge (HID) lamps, 97incandescent lamps, 68

Lamp lumen depreciation (LLD):illuminance calculations, 130table, 262–263

Lens:eye, 4–6refraction, 113, 114–115

Lensed wall-washers, asymmetric wash lights, 171,172–175, 176

Life cycle costs, electricity, 138–139Light:

direction and distribution of, 25–31elements of, psychology, 14, 16–18emotional impact, 11visible, perception, 3–6

Light control, 105–120glare, 118–120reflection, 105–109 (See also Reflection)refraction, 111–118 (See also Refraction)transmission, 109, 111

Light loss factor (LLF), illuminance calculations, 130Light measurement. See PhotometricsLight output:

fluorescent lamps, 91high-intensity discharge (HID) lamps, 97incandescent lamps, 68–69

Linear wall-wash lights, 179–182Louvers:

glare control, 116, 119object lights, 197rectilinear fluorescent downlights, 168shading devices, 58–59

Low-contrast environment, 12–13, 14Low-load degree of stimulation, 11–12Low-pressure sodium (LPS) lamps, described, 97–98Low-voltage control systems, 147Low-voltage incandescent lamps:

described, 75–77dimming control, 144–145

Lumen-maintenance controls, energy managementcontrols, 148

Luminaire(s), 149–208downlights:

luminous ceilings, 168–169point source, 154–166rectilinear fluorescent downlights, 166–168spacing criterion, 168

housings, 149–154light direction and distribution, 25–31

luminous intensity distribution curve, 123–124multidirectional, 198, 202–208

decorative, 202, 204–208direct-indirect, 198, 202

object lights, 186–197, 194–197task lights, 197–201visual clarity, 210–213wash lights, 169–193

asymmetric, 169–178ceiling plane, 182–193linear, 179–182

Luminaire dirt depreciation (LDD):illuminance calculations, 130table, 265

Luminaire maintenance categories, table, 264Luminance:

brightness, 6, 8brightness compared, 25photometrics, 121

Luminance ratios, design, balance of brightness, 234,236

Luminous ceilings, downlights, 168–169Luminous intensity distribution curve, photometrics,

123–124

MMagnetic transformer, described, 99–100Magnetic-transformer low-voltage dimmer, 145Manual switch control, 139–140Matte vertical surface illumination, design, 216–218Measurement. See PhotometricsMercury switch, 139Mercury vapor, high-intensity discharge (HID) light,

49, 93Mesopic vision, 5Metal halide lamps:

color, 49high-intensity discharge (HID) lamps, 93–94

Motorized controls, shading devices, 57–58Movable controls, shading devices, 57–58Multidirectional light, 25, 27, 29–30Multidirectional luminaires, 198, 202–208

decorative, 202, 204–208direct-indirect, 198–202

Multifaceted mirror-reflector (MR) lamp, 76–77Myopic vision, 5

NNeon, cold-cathode fluorescent lamp, 82Nondirectional incandescent lamps, 69, 70, 71

OObject lights, 186–197, 194–197

289

I N D E X

Open-reflector downlight, point source downlights,154, 157

Open-reflector wall-washers, asymmetric wash lights,171, 176–177

Overhangs, shading devices, 58, 59

PPaintings, artwork lighting design, 224–227Paper-based tasks, task lights, 220Parabolic aluminized reflector (PAR) incandescent

lamps, 71, 72Parabolic contour reflector, described, 107Parabolic louvers, rectilinear fluorescent downlights,

168Parallel circuit, described, 136–137Pendant-mounted housings, luminaires, 154, 155Perception, 3–10. See also Psychology

brain, 6brightness, 6, 8color, 9–10, 43–44eye, 4–6sight, 10three-dimensional form, 35, 224visible light, 3–6

Perceptual clarity, subjective impressions, 20–22Photometers, 8Photometrics, 121–134

illuminance calculations, 126–133limitations of, 121–123luminous intensity distribution curve, 123–124recommended illuminance values, 124–126surface reflectance, 133–134terms in, 121

Photopic vision, 5Photosensors:

daylight energy control, 62energy management controls, 147–148switch control, 140–141

Pinhole, image formation, 4–5Pleasantness, subjective impressions, 22Point source downlights, 154–166Polar graph, luminous intensity distribution curve,

122, 123–124Power factor, ballast systems, 101–102Power line carrier systems, 147Pre-heat ballast circuits, fluorescent lamps, 83–84Presbyopia, 5Prismatic lenses, rectilinear fluorescent downlights,

168Prisms:

refraction, 114visible light, 3–4

Private space, perceptual clarity, 22Psychology, 11–23. See also Perception

brightness contrast, 12–14degrees of stimulation, 11–12emotional impact, 11light elements, 14, 16–18subjective impressions, 18–23, 46, 122, 123three-dimensional form, 35variation, 23

Public space, perceptual clarity, 20–22Pulse-start metal halide lamps, 93–94Pupil, eye, 5Purkinje shift, 9

QQuartz, tungsten-halogen lamps, 74

RRadio-controlled wireless remote switch control, 141Rapid-start ballast circuits, fluorescent lamps, 85–86Rare-earth fluorescent light:

color, 48–49types of, 86–87

Recessed housings, luminaires, 149, 150Recommended illuminance values:

age level, 125–126photometrics, 124–126table of, 267–268

Rectilinear fluorescent downlights, 166–168Rectilinear graph, luminous intensity distribution

curve, 123–124Reflectance, surface finishes and, brightness, 31Reflected glare, described, 39–41Reflected sparkle, described, 41Reflection, 105–109

contours, 106–108circular, 107–108elliptical, 107parabolic, 107

diffuse, 105–106reflector types, 108–109

diffuse, 109, 110materials, 109semi-specular, 108specular, 108

semi-specular (spread), 105specular, 105total internal reflection, light control, 115, 118upward light, 26

Reflector(s):glare control, 119–120point source downlights, 164–166

Reflector (R) fluorescent lamps, 87–88Reflector (R) incandescent lamps, 71, 72, 73Reflector wall-washers, asymmetric wash lights, 171–

178

290


Refraction, 111–118baffles, 116lenses, 113, 114–115louvers, 116mechanics of, 111–112prisms, 112, 114solutions, 117total internal reflection, 115, 118

Relative brightness for equal attraction table,259

Relative lamp watts for equal quantity of light table,259

Rendering, color, 45–46Resistance, electricity, 135–136Resistance dimmers, 141–142Resistor, electricity, 135Retina, eye, 5, 7Rheostat, 141–142Rods, eye, 5, 8, 9Romex, electrical wiring, 136Room cavity ratio, illuminance calculations, 131

SScallop patterns, vertical surface illumination, 214–

216Scintillation, sparkle, 17Scotopic vision, 5Seasonal change, shading, 61Secondary light source, surface finishes and

reflectance, 31Semi-diffuse (spread) transmission, light control, 111Semi-directional incandescent lamps, 69, 71Semi-recessed housings, luminaires, 149, 151Semi-specular reflector, described, 108Semi-specular (spread) reflection, described, 105Series circuit, described, 136Service panel, electric distribution, 138Shading devices, 56–60, 61

movable controls, 57–58stationary controls, 58–60, 61

Shadows, design, balance of brightness, 236–237Shallow-contour downlights, point source downlights,

158, 162Shieldings, rectilinear fluorescent downlights, 167–

168Sight, perception, 10Silicon-controlled switch (SCS), solid-state dimmers,

142Silver-bowl incandescent lamps, 69, 71Sines and cosines of angles:

refraction, 112table, 261

Single-pole, double-throw switch, 139–140Single-pole, single-throw switch, 139

Skylights. See also Daylightdefined, 51design, 53–54, 55–56shading devices, 59, 60

Small-cell parabolic louvers, rectilinear fluorescentdownlights, 168

Sodium, high-intensity discharge (HID) light, 49, 93,94

Soffits, task lights, 197–201Solid-state dimmers, 142Spacing criterion, downlights, 168Spaciousness, subjective impressions, 18, 20Sparkle:

brightness, 41–42light elements, 14, 16–17, 18

Spectral distribution, color, 43–45Specular reflection, described, 105Specular reflector, described, 108Specular surfaces, reflected glare, 39Specular vertical surface illumination, design, 218Speed of light, 3Spread reflection. See Semi-specular (spread)

reflectionSquare law dimming curve, dimming control, 143Stationary controls, shading devices, 58–60, 61Stimulation, degrees of, psychology, 11–12Stroboscopic effect, fluorescent lamps, 92Subjective impressions:

brightness, 122, 123color, 46psychology, 18–23three-dimensional form, 35

Sunlight, defined, 51. See also DaylightSurface-mounted housings, luminaires, 149, 152–

154Surface reflectance:

brightness, 31photometrics, 133–134

Suspended ceiling system, rectilinear fluorescentdownlights, 167

Switch control, 139–141manual, 139–140occupancy sensors, 140photosensors, 140–141timers, 140wireless remote, 141

TTask lights:

design, 218–220light elements, 14, 16, 17, 18luminaires, 197–201

T8 fluorescent lamps, rare-earth phosphores, 86–87.See also Fluorescent lamps

291

I N D E X

Temperature, color, 45Texture, grazing light, 33–34T5 fluorescent lamps, rare-earth phosphores, 86–87.

See also Fluorescent lampsThree-dimensional form:

artwork lighting design, 224brightness, 31, 33–35

Three-way switch, 140Timers, switch control, 140Toggle switch, 139Total internal reflection, 115, 118Track-mounted luminaires, described, 154Transformers, described, 99–100Transmission, light control, 109, 111Transmitted sparkle, described, 41–42Trigger-start ballast circuits, fluorescent lamps, 86Trigonometric functions:

refraction, 112sines and cosines of angles, table, 261

Tubular skylights, daylight design, 55–56Tungsten, incandescent lamp filaments, 64, 68Tungsten-halogen lamps:

described, 73–75open-reflector downlight, 154

UUltraviolet lights, artwork lighting design, 227–229Uplights:

ambient light design, 221–224brightness, 25, 26–27, 28, 29ceiling plane wash lights, 183–184

VValences, multidirectional luminaires, 198, 202Variation:

daylight, 51psychology, 23reflected glare, 41

Vegetation, shading devices, 59–60Venetian blinds, shading devices, 57

Vertical surface illumination:artwork lighting design, 225brightness, 31design, 214–218subjective impressions, 23

Very-high output (VHO) lamps, fluorescent lamps, 87Video display terminals (VDTs):

ambient light, 221, 223–224luminance ratios, 236reflected glare, 39–41task lights, 219–220

Visible light, perception, 3–6Visual clarity, design, 209–213Visual comfort probability (VCP), defined, 39

WWall lighting:

brightness, 31subjective impressions, 23

Wash lights, 169–186asymmetric, 169–178ceiling plane, 182–193linear, 179–182matte vertical surface illumination, 216–218texture, 34

Wattage:incandescent lamps, 69power consumption, 138relative lamp watts for equal quantity of light, table,

259Watts per square foot calculations, 138Wavelengths:

color perception, 9, 43visible light, 3–4

Windows. See also Daylightdaylight design, 52–53glazing materials, 60

Wireless remote switch control, 141Wire size and length recommendations, table, 260Wiring, electricity, 136Workplane, brightness contrast, 11

292


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Interior Lighting