Lighting and Human Performance Lighting and Human Performance -- an an Overview

P R P R Boyce PhDPhDThe objective of this The objective of this

presentation is to show presentation is to show what we know and what what we know and what we do not know about we do not know about lighting and human lighting and human performance, as well as performance, as well as some interesting some interesting questions for researchquestions for research

Human Human Performance

Human Human PerformanceHuman performance is governed by many factors, lighting Human performance is governed by many factors, lighting

conditions being just one of themconditions being just one of them

Most visual tasks have at least three components: visual, Most visual tasks have at least three components: visual, cognitive and motor. Different visual tasks will have cognitive and motor. Different visual tasks will have different balances between these componentsdifferent balances between these components

We know something about visual performance in We know something about visual performance in photopic photopic conditionsconditions

We know less about visual performance in We know less about visual performance in mesopic mesopic conditionsconditions

We know very little about how lighting operates through We know very little about how lighting operates through mood or through the circadian system, other than that mood or through the circadian system, other than that it canit can

Visual Visual performance (Beutell / Weston 1935)

Visual performance is theVisual performance is thestudy of the effect ofstudy of the effect oflighting on the visuallighting on the visualcomponent of taskscomponent of tasks

Weston devised theWeston devised theLandolt Landolt Ring task andRing task andexplored the effects ofexplored the effects ofilluminanceilluminance, size and, size andcontrast contrast

He maximized the visualHe maximized the visualcomponentcomponent

Basic visual performance (Weston, 1945)

Principles of visual performanceWeston’s data showed four qualitative principles ofWeston’s data showed four qualitative principles ofvisual performance:visual performance:

1.1. Increasing Increasing illuminance illuminance shows a law of diminishing shows a law of diminishing returnsreturns

2.2. Saturation of performance occurs at lower Saturation of performance occurs at lower illuminances illuminances for large size, high contrast tasksfor large size, high contrast tasks

3.3. Increasing size and contrast is more effective than Increasing size and contrast is more effective than increasing increasing illuminanceilluminance

4.4. You cannot make the performance of a small size, low You cannot make the performance of a small size, low contrast task the same as a large size, high contrast contrast task the same as a large size, high contrast task by increasing the task by increasing the illuminanceilluminance

Numerical Verification Results (Rea, 1986)

Relative Visual Performance model (Rea, 1986)

RVP model (Rea, 1986)

The RVP model shows a nonThe RVP model shows a non--linear relationship between a task variable linear relationship between a task variable (contrast), a lighting variable (luminance) and relative visual (contrast), a lighting variable (luminance) and relative visual performance. performance.

This relationship is described as the plateau and escarpment of This relationship is described as the plateau and escarpment of visual visual performance performance

The RVP model was later refined, using reaction time to the onseThe RVP model was later refined, using reaction time to the onset of a t of a square stimulus as the measure (Rea and Ouellette, 1988, 1991)square stimulus as the measure (Rea and Ouellette, 1988, 1991)

These data were consistent with the earlier model, and showed thThese data were consistent with the earlier model, and showed the e effect of size as welleffect of size as well

This model has been independently validated (This model has been independently validated (Eklund Eklund et al, 2001)et al, 2001)

Limitations of the RVP model

The RVP model is valid for achromatic, onThe RVP model is valid for achromatic, on--axis visual tasks axis visual tasks seen in seen in photopic photopic conditionsconditions

Where the task containsWhere the task contains colour colour differences,performance will differences,performance will be maintained as luminance contrast tends to zerobe maintained as luminance contrast tends to zero

For offFor off--axis visual tasks, the trends will be the same but axis visual tasks, the trends will be the same but much exaggeratedmuch exaggerated

For For mesopic mesopic conditions, the effect of luminance will be conditions, the effect of luminance will be different for offdifferent for off--axis tasks done under different light axis tasks done under different light sources because the spectral sensitivity of the sources because the spectral sensitivity of the peripheral retina changesperipheral retina changes

Mesopic visionThe visual system has threeThe visual system has threeoperating states; operating states; photopicphotopic,,mesopic mesopic and and scotopicscotopic

In In photopic photopic vision, conevision, conephotoreceptors are dominantphotoreceptors are dominant

In In scotopic scotopic vision, rodvision, rodphotoreceptors are dominantphotoreceptors are dominant

In In mesopic mesopic vision, conevision, conephotoreceptors are active in thephotoreceptors are active in thefovea but both rod and conefovea but both rod and conephotoreceptors are active in thephotoreceptors are active in theperipheryperiphery

Mesopic visionThe spectral sensitivity of the visualThe spectral sensitivity of the visualsystem changes as the operatingsystem changes as the operatingstate changesstate changes

However, all photometricHowever, all photometricmeasurements are based on themeasurements are based on thespectral sensitivity of the conespectral sensitivity of the conephotoreceptors photoreceptors

This means that photometricThis means that photometricmeasurements may not accuratelymeasurements may not accuratelyreflect the effectiveness of differentreflect the effectiveness of differentlight sources in light sources in mesopic mesopic conditionsconditions

Much exterior lighting andMuch exterior lighting andemergency interior lighting provideemergency interior lighting providemesopic mesopic conditionsconditions

Mesopic Vision - laboratory studies (Lewis, 1999)

Mesopic vision - field studies (Akashi and Rea, 2001)

Measurements of Measurements of reaction time for the reaction time for the onset of offonset of off--axis reflecting axis reflecting targets while driving targets while driving under HPS and MH road under HPS and MH road lighting, with headlights lighting, with headlights turned on or offturned on or off

Reaction time is shorter Reaction time is shorter for MH road lightingfor MH road lighting

Models of mesopic photometry

Recently two models of Recently two models of mesopic mesopic photometry based on photometry based on performance have been publishedperformance have been published

Rea et al (2004) use reaction time for offRea et al (2004) use reaction time for off--axis detection axis detection as a basis. This model reaches as a basis. This model reaches photopic photopic photometry at photometry at 0.6 0.6 cdcd/m/m22

MOVE use the performance of a series of tasks related MOVE use the performance of a series of tasks related to driving as a basis. This model reaches to driving as a basis. This model reaches photopic photopic photometry at 10 photometry at 10 cdcd/m/m22

Unfortunately, much exterior lighting provides Unfortunately, much exterior lighting provides luminances luminances around 1 around 1 cdcd/m/m22. Work to determine the value . Work to determine the value of each model is urgently needed.of each model is urgently needed.

Predictions of modelsAt 1 At 1 cdcd/m/m22 ((photopicphotopic), the Rea et al (2004) ), the Rea et al (2004) model predicts no difference between HPS and model predicts no difference between HPS and MH. The MOVE model predicts that the HPS will MH. The MOVE model predicts that the HPS will produce 0.94 produce 0.94 cdcd/m/m22 and MH will produce 1.10 and MH will produce 1.10 cdcd/m/m22..

At 0.1 At 0.1 cdcd/m/m22 ((photopicphotopic) the Rea et al (2004) ) the Rea et al (2004) model predicts HPS will produce 0.074 model predicts HPS will produce 0.074 cdcd/m/m22

and MH will produce 0.127 and MH will produce 0.127 cdcd/m/m22. The MOVE . The MOVE model predicts that the HPS will produce 0.085 model predicts that the HPS will produce 0.085 cdcd/m/m22 and the MH will produce 0.125 and the MH will produce 0.125 cdcd/m/m22..

What is needed

Current road lighting standards suggest that Current road lighting standards suggest that photopic photopic measurements are adequate for major roads with average measurements are adequate for major roads with average luminances luminances greater than 1 greater than 1 cdcd/m/m22 but design for minor roads with but design for minor roads with lower average lower average luminances luminances would be better done using would be better done using mesopic mesopic luminancesluminances

For roads without lighting, where headlights are the source of For roads without lighting, where headlights are the source of illumination, light sources that more effectively stimulate the illumination, light sources that more effectively stimulate the rod rod photoreceptors should enable detection of targets at a greater photoreceptors should enable detection of targets at a greater distancedistance

The ability of the two models of The ability of the two models of mesopic mesopic photometry to predict photometry to predict performance in performance in mesopic mesopic conditions needs to be tested, particularly conditions needs to be tested, particularly at the at the mesopic mesopic / / photopic photopic boundary boundary

MoodMood depends on context and expectationsMood depends on context and expectations

Lighting the space and performance

Several attempts have beenSeveral attempts have beenmade in laboratory settingsmade in laboratory settings((Eklund Eklund et al, 2000, 2001;et al, 2000, 2001;Boyce et al, 2003)Boyce et al, 2003)

In these studies, the lightingIn these studies, the lightingconditions provided the sameconditions provided the sameilluminance illuminance on the task,on the task,without discomfort, butwithout discomfort, butdifferent lighting of the spacedifferent lighting of the space

No changes in taskNo changes in taskperformance were found,performance were found,except when size of detail wasexcept when size of detail waschangedchanged

Lighting the space and performance

This means that:This means that:

Only lighting conditions Only lighting conditions that change task visibility that change task visibility can be relied upon to can be relied upon to change performancechange performance

Lighting the space in Lighting the space in different ways may change different ways may change mood but so can many mood but so can many other things and lighting other things and lighting the space may be much the space may be much less potent than theseless potent than these

Base Case Best Practice

Best Practice + Switchable Control Dimming Control

Do people see a difference? (Boyce et al, 2006)

Lighting the space changes the percentage satisfied (Boyce et al, 2006)

Percentage considering the lighting comfortable:Percentage considering the lighting comfortable:

Regular array of parabolic Regular array of parabolic luminaires luminaires = 71%= 71%Regular array of prismatic Regular array of prismatic luminaires luminaires = 69%= 69%Linear array of direct/indirect Linear array of direct/indirect luminaires luminaires plus wall washing = 85%plus wall washing = 85%One direct/indirect One direct/indirect luminaire luminaire with individual control over each cubiclewith individual control over each cubicleplus wall washing = 91%plus wall washing = 91%

Percentage considering the lighting better than usual for an offPercentage considering the lighting better than usual for an office: ice:

Regular array of parabolic Regular array of parabolic luminaires luminaires = 24%= 24%Regular array of prismatic Regular array of prismatic luminaires luminaires = 21%= 21%Linear array of direct/indirect Linear array of direct/indirect luminaires luminaires plus wall washing = 53%plus wall washing = 53%One direct/indirect One direct/indirect luminaire luminaire with individual control over each cubiclewith individual control over each cubicleplus wall washing = 50%plus wall washing = 50%

Linked mechanism map found (Boyce et al, 2003)

ResultsResults

Personal Control

Luminous Conditions

Non-task Surface Brightness

Appraisal Visual Comfort Visual Capabilities

Preference

Mood (Affect)

Competence

Motivation

Health and Well-Being

Task Performance

What does this mean?It means that, in this and similar studies, changes in the visibIt means that, in this and similar studies, changes in the visibilityilityof the task change task performance but the lighting of the spacof the task change task performance but the lighting of the spaceedoes notdoes not

Task performance is governed by what happens in the task areaTask performance is governed by what happens in the task area

Lighting outside the task area may affect how people feel but noLighting outside the task area may affect how people feel but nottwhat they dowhat they do

This conclusion is based on a study done in a simulated office This conclusion is based on a study done in a simulated office with work done by people working for one day only. Given thewith work done by people working for one day only. Given thehigh level of motivation associated with taking part in anhigh level of motivation associated with taking part in anexperiment, such studies emphasize what people can do rather experiment, such studies emphasize what people can do rather than what they choose to dothan what they choose to do

What is needed?

To examine what people To examine what people choosechooseto do rather than what they to do rather than what they cancando. For working spaces, it isdo. For working spaces, it isnecessary to examine thenecessary to examine thebehavior of people behavior of people

doing their normal jobdoing their normal job

over several monthsover several months

in different visual in different visual environmentsenvironments

and measuring organizational and measuring organizational efficiencyefficiency

Light operating through the circadian system

The circadian The circadian system provides system provides timing of the sleep timing of the sleep / wake cycle and / wake cycle and many other many other physiological physiological functionsfunctions

Exposure to a light Exposure to a light / dark cycle / dark cycle entrains the entrains the circadian systemcircadian system

Light operating through the circadian system

Spectral sensitivity of the Spectral sensitivity of the circadian system is not the circadian system is not the same as the visual system same as the visual system ((Brainard Brainard et al, 2001; et al, 2001; Thapan Thapan et al, 2001)et al, 2001)

There is a new There is a new photoreceptor in the retina photoreceptor in the retina for the circadian systemfor the circadian system

There is evidence for There is evidence for opponency opponency (Rea et al, (Rea et al, 2005) This suggests that 2005) This suggests that cones interact with the new cones interact with the new photoreceptorphotoreceptor

Light operating through the circadian system (Jewett et al, 1997)

Exposure to light at Exposure to light at the right time can the right time can advance or delay advance or delay the phase of the the phase of the sleep / wake cyclesleep / wake cycle

Exposure to bright Exposure to bright light at night can light at night can increase alertnessincrease alertness

Light operating through the circadian system

Exposure to light at the Exposure to light at the appropriate time can be appropriate time can be used to make faster used to make faster adjustments when the sleep adjustments when the sleep / wake cycle is misaligned, / wake cycle is misaligned, e.g., starting night shift work e.g., starting night shift work or after crossing multiple or after crossing multiple time zonestime zones

To be effective it is To be effective it is necessary to have control of necessary to have control of light exposure over the light exposure over the whole 24 hourswhole 24 hours

Light operating through the circadian system

Exposure to light at night Exposure to light at night can be used to increase can be used to increase alertness (alertness (Cajochen Cajochen et al, et al, 2000)2000)

But exposure to light at night But exposure to light at night has also been shown to has also been shown to increase the rate of growth increase the rate of growth of breast cancer of breast cancer tumours tumours ((Blask Blask et al, 2005) et al, 2005)

What is needed

There is still much to learn about the nonThere is still much to learn about the non--visual effects of visual effects of light, including possible side effects, so more research is light, including possible side effects, so more research is definitely neededdefinitely needed

The possibility of long term side effects suggests we The possibility of long term side effects suggests we should be careful how we apply light for nonshould be careful how we apply light for non--visual visual purposespurposes

The $64,000,000 question is whether or not there is a The $64,000,000 question is whether or not there is a beneficial effect of light exposure on healthy people during beneficial effect of light exposure on healthy people during the daythe day

Conclusion

The field of lighting and human performance is slowly The field of lighting and human performance is slowly being extended away from the certain effects of lighting on being extended away from the certain effects of lighting on vision, but in two different directionsvision, but in two different directions

In one direction lies the effects of lighting on mood, where In one direction lies the effects of lighting on mood, where any effect on performance will always be a matter of any effect on performance will always be a matter of probability rather than certaintyprobability rather than certainty

In the other direction lies the effects of light on the In the other direction lies the effects of light on the underlying human physiology that sets the platform from underlying human physiology that sets the platform from which we operatewhich we operate

We still have much to learnWe still have much to learn