OCULAR LIGHTING EFFECTSON HUMAN PHYSIOLOGY,MOOD AND BEHAVIOUR

CIE 15x:2003

UDC: 612.014.481-06 Descriptor: Optical radiation effects on human

ISBN 3 901 906 xx x

Deadline for BA and D6 votes:

11.09.2003

THE INTERNATIONAL COMMISSION ON ILLUMINATION

The International Commission on Illumination (CIE) is an organisation devoted to international co-operation and exchange ofinformation among its member countries on all matters relating to the art and science of lighting. Its membership consists ofthe National Committees in 37 countries and one geographical area and of 5 associate members.

The objectives of the CIE are :1. To provide an international forum for the discussion of all matters relating to the science, technology and art in the fields

of light and lighting and for the interchange of information in these fields between countries.2. To develop basic standards and procedures of metrology in the fields of light and lighting.3. To provide guidance in the application of principles and procedures in the development of international and national

standards in the fields of light and lighting.4. To prepare and publish standards, reports and other publications concerned with all matters relating to the science,

technology and art in the fields of light and lighting.5. To maintain liaison and technical interaction with other international organisations concerned with matters related to the

science, technology, standardisation and art in the fields of light and lighting.The work of the CIE is carried on by seven Divisions each with about 20 Technical Committees. This work covers subjectsranging from fundamental matters to all types of lighting applications. The standards and technical reports developed by theseinternational Divisions of the CIE are accepted throughout the world.A plenary session is held every four years at which the work of the Divisions and Technical Committees is reviewed, reportedand plans are made for the future. The CIE is recognised as the authority on all aspects of light and lighting. As such itoccupies an important position among international organisations.

LA COMMISSION INTERNATIONALE DE L'ÉCLAIRAGE

La Commission Internationale de l'Éclairage (CIE) est une organisation qui se donne pour but la coopération internationale etl'échange d'informations entre les Pays membres sur toutes les questions relatives à l'art et à la science de l'éclairage. Elleest composée de Comités Nationaux représentant 37 pays plus un territoire géographique, et de 5 membres associés.

Les objectifs de la CIE sont :6. De constituer un centre d'étude international pour toute matière relevant de la science, de la technologie et de l'art de la

lumière et de l'éclairage et pour l'échange entre pays d'informations dans ces domaines.7. D'élaborer des normes et des méthodes de base pour la métrologie dans les domaines de la lumière et de l'éclairage.8. De donner des directives pour l'application des principes et des méthodes d'élaboration de normes internationales et

nationales dans les domaines de la lumière et de l'éclairage.9. De préparer et publier des normes, rapports et autres textes, concernant toutes matières relatives à la science, la

technologie et l'art dans les domaines de la lumière et de l'éclairage.10. De maintenir une liaison et une collaboration technique avec les autres organisations internationales concernées par des

sujets relatifs à la science, la technologie, la normalisation et l'art dans les domaines de la lumière et de l'éclairage.Les travaux de la CIE sont effectués par 7 Divisions, ayant chacune environ 20 Comités Techniques. Les sujets d'étudess'étendent des questions fondamentales, à tous les types d'applications de l'éclairage. Les normes et les rapports techniquesélaborés par ces Divisions Internationales de la CIE sont reconnus dans le monde entier.Tous les quatre ans, une Session plénière passe en revue le travail des Divisions et des Comités Techniques, en fait rapportet établit les projets de travaux pour l'avenir. La CIE est reconnue comme la plus haute autorité en ce qui concerne tous lesaspects de la lumière et de l'éclairage. Elle occupe comme telle une position importante parmi les organisationsinternationales.

DIE INTERNATIONALE BELEUCHTUNGSKOMMISSION

Die Internationale Beleuchtungskommission (CIE) ist eine Organisation, die sich der internationalen Zusammenarbeit unddem Austausch von Informationen zwischen ihren Mitgliedsländern bezüglich der Kunst und Wissenschaft der Lichttechnikwidmet. Die Mitgliedschaft besteht aus den Nationalen Komitees in 37 Ländern und einem geographischen Gebiet und aus 5assoziierten Mitgliedern.

Die Ziele der CIE sind :11. Ein internationaler Mittelpunkt für Diskussionen aller Fragen auf dem Gebiet der Wissenschaft, Technik und Kunst der

Lichttechnik und für den Informationsaustausch auf diesen Gebieten zwischen den einzelnen Ländern zu sein.12. Grundnormen und Verfahren der Meßtechnik auf dem Gebiet der Lichttechnik zu entwickeln.13. Richtlinien für die Anwendung von Prinzipien und Vorgängen in der Entwicklung internationaler und nationaler Normen

auf dem Gebiet der Lichttechnik zu erstellen.14. Normen, Berichte und andere Publikationen zu erstellen und zu veröffentlichen, die alle Fragen auf dem Gebiet der

Wissenschaft, Technik und Kunst der Lichttechnik betreffen.15. Liaison und technische Zusammenarbeit mit anderen internationalen Organisationen zu unterhalten, die mit Fragen der

Wissenschaft, Technik, Normung und Kunst auf dem Gebiet der Lichttechnik zu tun haben.Die Arbeit der CIE wird in 7 Divisionen, jede mit etwa 20 Technischen Komitees, geleistet. Diese Arbeit betrifft Gebiete mitgrundlegendem Inhalt bis zu allen Arten der Lichtanwendung. Die Normen und Technischen Berichte, die von dieseninternational zusammengesetzten Divisionen ausgearbeitet werden, sind von der ganzen Welt anerkannt.Tagungen werden alle vier Jahre abgehalten, in der die Arbeiten der Divisionen überprüft und berichtet und neue Pläne für dieZukunft ausgearbeitet werden. Die CIE wird als höchste Autorität für alle Aspekte des Lichtes und der Beleuchtungangesehen. Auf diese Weise unterhält sie eine bedeutende Stellung unter den internationalen Organisationen.

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Tel: +43(01)714 31 87 0, Fax: +43(01)713 08 38 18e-mail: ciecb@ping.at

WWW: http://www.cie.co.at/cie/ CIE 2003 – All rights reserved

OCULAR LIGHTING EFFECTSON HUMAN PHYSIOLOGY,MOOD AND BEHAVIOUR

CIE 15x:2003

UDC: 612.014.481-06 Descriptor: Optical radiation effects on human

ISBN 3 902 906 xx x

CIE 15x:2003

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This Technical Report has been prepared by CIE Technical Committee 6-11 of Division 6“Photobiology and Photochemistry” and has been approved by the Board of Administration ofthe Commission Internationale de l'Eclairage for study and application. The document reportson current knowledge and experience within the specific field of light and lighting described,and is intended to be used by the CIE membership and other interested parties. It should benoted, however, that the status of this document is advisory and not mandatory. The latestCIE proceedings or CIE NEWS should be consulted regarding possible subsequentamendments.

Ce rapport technique a été élaboré par le Comité Technique CIE 6-11 de la Division 6“Photobiologie et Photochimie” et a été approuvé par le Bureau de la CommissionInternationale de l'Eclairage, pour étude et emploi. Le document expose les connaissances etl'expérience courantes dans le domaine particulier de la lumière et de l'éclairage décrit ici. Ilest destiné à être utilisé par les membres de la CIE et par tout les intéressés. Il fautcependant noter que ce document est indicatif et non obligatoire. Il faut consulter les plusrécents comptes rendus de la CIE, ou le CIE NEWS, en ce qui concerne des amendementsnouveaux éventuels.

Dieser Technische Bericht ist vom CIE Technischen Komitee 6-11 der Division 6“Photobiologie und Photochemie” ausgearbeitet und vom Vorstand der CommissionInternationale de l'Eclairage gebilligt worden. Das Dokument berichtet über den derzeitigenStand des Wissens und Erfahrung in dem behandelten Gebiet von Licht und Beleuchtung; esist zur Verwendung durch CIE-Mitglieder und durch andere Interessierte bestimmt. Es solltejedoch beachtet werden, daß das Dokument eine Empfehlung und keine Vorschrift ist. Dieneuesten CIE-Tagungsberichte oder das CIE NEWS sollten im Hinblick auf mögliche spätereÄnderungen zu Rate gezogen werden.

Any mention of organisations or products does not imply endorsement by the CIE. Whilstevery care has been taken in the compilation of any lists, up to the time of going to press,these may not be comprehensive.

Toute mention d'organisme ou de produit n'implique pas une préférence de la CIE. Malgré lesoin apporté à la compilation de tous les documents jusqu'à la mise sous presse, ce travail nesaurait être exhaustif.

Die Erwähnung von Organisationen oder Erzeugnissen bedeutet keine Billigung durch dieCIE. Obgleich große Sorgfalt bei der Erstellung von Verzeichnissen bis zum Zeitpunkt derDrucklegung angewendet wurde, ist es möglich, daß diese nicht vollständig sind.

CIE 2003– All rights reserved

CIE 15x:2003

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The following members of TC 6-11, “Systemic Effects of Optical Radiation on the Human” tookpart in the preparation of this technical report. The committee comes under Division 6“Photobiology and Photochemistry”.

Members:

Jennifer A. Veitch (Chair) Canada

Gerrit van den Beld the Netherlands

George Brainard USA

Joan E. Roberts USA

Acknowledgements:

The committee would like to thank those who, although not members of the committee,contributed or reviewed sections of this report: D. Blask, S. W. Lockley, I. Provencio, and A.Wiechmann. Illustrations were provided by: G. Franche, D. Hobbs, C. Reinhart, D. Skene, andK. Voss.

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CONTENTS

SUMMARY VI

RESUME VI

ZUSAMMENFASSUNG VI

1. INTRODUCTION 1

1.1 Biological, psychological and architectural issues 1

1.2 Terms of reference 1

2. NEUROPHYSIOLOGY OF LIGHT AND DARK 2

2.1 Rhythms of activity 2

2.2 Circadian rhythms 2

2.2.1 Brain structures controlling circadian rhythms 3

2.2.2 Light and circadian rhythms 4

2.3 Melatonin 4

2.3.1 Melatonin circadian rhythms 4

2.3.2 Acute light suppression 5

2.3.3 Health and melatonin cycles 6

2.4 Cortisol 7

2.5 Other biological functions 7

2.6 Photoimmune responses 8

3. OCULAR ANATOMY AND PHYSIOLOGY 9

3.1 The visual system 9

3.2 Nonvisual photoperception 10

3.2.1 Location of nonvisual photoreceptors 10

3.2.2 Ocular photoreceptors 10

3.2.3 Retinal location of nonvisual photoreceptors 12

3.3 Circadian rhythms of ocular sensitivity 13

3.4 Age and ocular sensitivity 13

4. BEHAVIOURAL EFFECTS IN HEALTHY PEOPLE 14

4.1 Circadian rhythms of behaviour 14

4.2 Effects of daytime light exposure 14

4.2.1 Activation and arousal 14

4.2.2 Performance 15

4.2.3 Mood and comfort 16

4.3 Effects of night-time light exposure 17

4.3.1 Alertness 17

4.3.2 Performance 17

4.3.2 Mood 18

4.4 Circadian phase shifting 18

4.4.1 Jet lag 18

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4.4.2 Shift work 19

4.5 Luminous modulation 20

5. THERAPEUTIC EFFECTS OF LIGHT 21

5.1 Mood disorders 21

5.1.1 Seasonal mood disorders 21

5.1.2 Other mood disorders 23

5.2 Sleep disorders 23

5.3 Circadian rhythms and medical treatment 24

5.4 Neurological disorders: Alzheimer and related dementias 24

6. RESEARCH METHODS IN LIGHTING 25

6.1 Measuring light 25

6.1.1 Stimulus specification 25

6.1.2 Photometric measurement 25

6.2 Light exposure and light dose 26

6.3 Research design issues 27

6.3.1 Placebo effects 27

6.3.2 Eliminating alternative explanations 27

6.3.3 Size and composition of research samples 28

7. ARCHITECTURAL AND LIFE-STYLE APPLICATIONS 28

7.1 General principles 28

7.1.1 Principles for healthy lighting 28

7.1.2 Fundamentals of lighting quality 29

7.2 Lighting for daytime activity 30

7.3 Lighting for night shifts 31

8. CONCLUSION 31

9. REFERENCES 32

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OCULAR LIGHTING EFFECTS ON HUMAN PHYSIOLOGY, MOOD AND BEHAVIOUR

SUMMARY

The nonvisual biological and behavioural effects of light in animals and humans are mediatedby specific neuroanatomical pathways. Controlled empirical studies have shown that light canbe used to treat some clinical disorders and may have broader, nonclinical applications forproblems of shift work and jet lag. Studies are testing how lighting may be incorporated intoarchitectural designs that are optimal for vision as well as physiological and behaviouralstimulation.

FRENCH TITLE

RESUME

Translation requested

GERMAN TITLE

ZUSAMMENFASSUNG

Translation requested

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1. INTRODUCTION

1.1 Biological, psychological and architectural issues

In the late 1990s, CIE began to shift its emphasis from lighting for visibility to a more broaddefinition of lighting quality, encompassing human needs, architectural integration, andeconomic constraints (including energy) (Veitch, 1998; Veitch, Julian, & Slater, 1998) (Figure1). Human needs, as defined here, include lighting that is appropriate to maintain good health,as well as lighting for visibility, task performance, interpersonal communication, and aestheticappreciation.

Figure 1. Lighting quality model. From Veitch (1998), courtesy of the National ResearchCouncil of Canada.

Among other developments, this definition reflects the many demonstrations thatthere are nonvisual, systemic effects of light in humans. Specifically, controlled laboratory andclinical studies have demonstrated that light processed through the eye can influence humanphysiology, mood and behaviour (Aschoff, 1981; Lam, 1998; Society for Research onBiological Rhythms, 1988; Society for Research on Biological Rhythms, 1995; Wetterberg,1993; Wurtman, Baum, & Potts, 1985). These findings may provide the basis for majorchanges in future architectural lighting strategies.

At least five characteristics of light are known to be implicated in these effects:intensity, spectrum, timing, duration, and pattern of exposure. The importance of timing isunderscored in this report by treating daytime and night-time exposures separately. Theeffects of varying light intensities are discussed throughout. Much of what is known aboutspectral effects concerns photodetection, and is discussed under that heading.

1.2 Terms of reference

Interest in the biological and psychological effects of light, apart from vision, has dramaticallyincreased since the 1980s (Lavie, 2001). This interest both stimulated the formation of severalCIE technical committees concerned with such topics, and complicated the task of writingdefinitive reports. The science continues to evolve. When, after many years of existence, thecommittee had not completed its work because of the rapid development in the field ofphotobiology, this technical committee set a more modest goal. The following terms ofreference adopted at the 1995 CIE Session in New Delhi, India:

TERMS OF REFERENCE: Provide the CIE with a concise summary document on thesystemic effects of ocularly detected optical radiation with the relevant, key scientificreferences. Specifically the document will introduce the controlled laboratory and clinicalstudies on the effects of light on human physiology, mood and behaviour. Studies on useof ocular light therapy for clinical disorders as well as for improving human adaptation to

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shift work and intercontinental jet travel will be discussed. How these new findings maychange future architectural lighting strategies will be considered.

The report is based on an invited address by Brainard and Bernecker at the CIEsession in New Delhi (Brainard & Bernecker, 1996), updated and expanded in some areas.For example, expansion of interest in the new area of photoimmunology (Roberts, 1995;Roberts, 2000) has led the committee to add this area to its report. This report is based onpublished work up to February 2002, when it was written.

Another CIE technical committee report that relates to this topic is TC 6-16,"Psychobiological effects of lighting", which has produced an extensive annotated bibliography(CIE, 2001a). CIE Technical Committee TC 3-16, "Psychological Aspects of Lighting" alsoconcerns related research. At time of writing this committee had produced a draft report buthad not completed final editing or division balloting, and it is not known when the report will bepublicly available. These reports should be read together for a complete picture of the state ofknowledge in this area as of the late 1990s/early 2000s.

2. NEUROPHYSIOLOGY OF LIGHT AND DARK

2.1 Rhythms of activity

Many biological functions are rhythmic, increasing and decreasing in level following a constantcyclic pattern. Different processes cycle at different rates, characterised by the frequency withwhich they complete a cycle (i.e., the period of the oscillation, for example from peak to peak).Four rhythms have specific definitions in terms of their frequency, as follows:

• ultradian: a rhythm with a period shorter than one day, but longer than one hour (e.g., thenon-rapid eye movement (NREM) – rapid eye movement (REM) sleep cycle occursapproximately every 90 minutes during sleep)

• circadian: a rhythm with a period of approximately 24 hours (e.g., hormonal melatoninrhythm, core body temperature, sleeping and waking - discussed further below)

• infradian: a rhythm with a period longer than a day (e.g., menstrual cycles occurapproximately every four weeks)

• circannual: a rhythm with a period of approximately one year (e.g., seasonal changes inhormone secretion (e.g., Wehr, 1991))

Biological rhythms also differ in amplitude, or the degree of difference between thepeak level and the mesor. Some show dramatic changes over the period of the cycle; a well-known example is the infradian rhythm of estrogen secretion in adult women. Circannualchanges in hormone secretion in humans, by contrast, have low amplitude.

2.2 Circadian rhythms

For the purposes of this report, the major focus is on circadian rhythms. In general, thecircadian system is responsible for controlling daily rhythms such as sleep and wakefulness,body temperature, hormonal secretion, and other physiological parameters including cognitivefunction and immune responses. The human circadian rhythm has an average period close to24 (24,2 h), with a range in sighted, healthy subjects from ~23,9 to 24,5 h (Czeisler et al.,1999). Light detected by the eyes is the primary environmental stimulus for regulating thecircadian system, although other external stimuli such as sound, temperature, social cues,caffeine, and meal times may also influence the body's timing functions (Aschoff, 1981;Binkley, 1990; Klein, Moore, & Reppert, 1991; Klerman et al., 1998; Lakin-Thomas, 1997;Wetterberg, 1993). Age might modify circadian amplitude (Arendt, 1998a; Jean-Louis et al.,2000) but does not appear to change the period of the cycle (Czeisler, Duffy et al., 1999).

Figure 2 shows four important circadian rhythms schematically, to illustrate theconcurrent biological rhythms over each day. It shows two full cycles (48 hours) of peaks andnadirs. Alertness is shown peaking at approximately 13H00, with its nadir at approximately04H00. Conversely, secretion of the hormone melatonin is lowest during the day, and peakswhen alertness is lowest. Core body temperature peaks ahead of melatonin secretion and

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reaches its nadir shortly after the melatonin peak. Secretion of cortisol, another endocrinehormone, peaks approximately four hours after melatonin. Later sections discuss thesepatterns and hormones in greater detail.

Figure 2. Schematic diagram of four circadian rhythms shows the rise and fall of alertnessand core body temperature, and the secretion rates of two hormones, cortisol and melatonin.The diagram does not show absolute levels, but illustrates the differences in the timing ofpeaks and valleys against clock time and the different shapes of the rhythms. © PhilipsLighting, ALC, 2001, courtesy of Philips Lighting.

2.2.1 Brain structures controlling circadian rhythms

As shown in Figure 3, a neural pathway called the retinohypothalamic tract (RHT), projectsfrom the retina into a non-visual part of the brain called the hypothalamus (Aschoff, 1981;Card, 1994; Klein et al., 1991; Klein et al., 1983; Moore & Lenn, 1972; Pickard & Silverman,1981). The hypothalamus is a complex neural region that controls many basic functions of thebody including hormonal secretion, core temperature, metabolism and reproduction as well ashigher neural functions such as memory and emotion (Morgane & Panksepp, 1979). A pair ofspecific hypothalamic nuclei, the suprachiasmatic nuclei (SCN), are the principal terminationof the RHT (Klein et al., 1991; Moore & Lenn, 1972; Pickard & Silverman, 1981). Thesebilateral nuclei are considered to be fundamental parts of the "biological clock", or circadiansystem, which regulates the body's physiological rhythms (Aschoff, 1981). Advances ingenetics have begun to unravel the circadian clock mechanism in the SCN at the molecularlevel (Devlin & Kay, 2001; Reppert & Weaver, 2001).

Figure 3. Schematic diagram of eye-brain pathways. Light received by the eye is converted toneural signals that pass via the optic nerve to two pathways, one visual and one non-visual.RHT = Retino-hypothalamic tract. IGL = Intergeniculate leaflet. SCN = Suprachiasmaticnucleus of the hypothalamus. PVN = Paraventricular nucleus of the hypothalamus.IMLCC = Intermediolateral cell column. SCG = Superior cervical ganglion.CRH = Corticotropic releasing hormone. ACTH = adrenocorticotropic hormone.

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The SCN relay photic and non-photic information to various control centres in thenervous system including other hypothalamic nuclei, the septal nuclei, the thalamus, themidbrain and the spinal cord (Klein et al., 1991). These systems regulate the production ofalmost all hormones, including cortisol, thyroid-stimulating hormone, and melatonin (whichhave large-amplitude circadian rhythms), and insulin, growth hormone, prolactin andluteinizing hormone (which have smaller-amplitude daily rhythms, some of which differbetween men and women) (Czeisler & Klerman, 1999; Wehr, 1998). Thus, light exposureinfluences a wide variety of physiological functions, in relationships that are not entirely well-understood as yet but that are under active investigation (Buijs, Hermes, & Kalsbeek, 1998;Morin, 1999; Partonen, 2000).

The neural pathway responsible for vision is anatomically separate from the pathwayresponsible for circadian regulation. There is, however, a functional connection between theprimary visual pathway and the circadian neuroanatomy by way of the intergeniculate leaflets(IGL) (Horvath, 1998; Morin, 1994). Although the retinohypothalamic tract has its densestprojection in or around the suprachiasmatic nuclei, this pathway has diffuse projections toother hypothalamic nuclei (preoptic nuclei, anterior and lateral hypothalamic areas,retrochiasmatic area and dorsal nuclei) as well as nuclei outside the hypothalamus (thalamicIGL, midbrain periaqueductal grey) (Card, 1994; Klein et al., 1991). The functional roles ofthese and other nonvisual projections from the retina are under active investigation.

2.2.2 Light and circadian rhythms

Numerous studies on biological responses of humans to bright artificial light have confirmedthat light entering the eyes is a potent stimulus for controlling circadian rhythms (Brainard etal., 1988; Czeisler et al., 1986; Czeisler et al., 1990; Lam, 1998; Lewy, Sack, Miller, & Hoban,1987; Minors , Waterhouse, & Wirz-Justice, 1991; Shanahan & Czeisler, 1991; Wetterberg,1993; Wurtman et al., 1985). The effect of light exposure differs depending on the timing inrelation to the endogenous circadian phase (Czeisler et al., 1986; Czeisler et al., 1989; Jewett,Kronauer, & Czeisler, 1994; Jewett et al., 1997; Minors et al., 1991; Shanahan & Czeisler,1991). Light exposure after the nadir of the body temperature cycle (i.e., in the morning)advances the phase of the body temperature cycle and the melatonin rhythm (so that the newcycles peak earlier); light exposure in the evening delays both the body temperature andmelatonin cycles (so that these cycles peak later than they would have) (Czeisler & Klerman,1999). Light exposure close to the core body temperature minimum may also directly suppresscircadian amplitude (Jewett et al., 1994).

The general principles of phase-shifting are well accepted, but the molecularmechanism underlying this physiology is under intensive investigation (Czeisler & Klerman,1999; Lakin-Thomas, 1997; Menaker, 1997; Reppert & Weaver, 2001). Much of ourknowledge about light input to the circadian system comes from studies of acute melatoninsuppression during night-time exposures, which are discussed below.

2.3 Melatonin

2.3.1 Melatonin circadian rhythms

In all vertebrate species studied to date, including humans, high levels of melatonin aresecreted during the dark phase of the photoperiod (night) and low levels are secreted duringthe light phase (day) (Aschoff, 1981; Wetterberg, 1993; Wurtman et al., 1985). Melatonin issynthesised from tryptophan, an amino acid, in a series of four enzymatic steps that includethe neurotransmitter serotonin as an intermediate step (Wiechmann, 1986). The activity of therate-limiting enzyme in the chain is higher at night than during the day, in response to neuralinformation about external light stimulation (Klein et al., 1997). The activity of the enzymes ateach step varies depending on the state of the circadian clock mechanism (Gillette &Tischkau, 1999). Thus, the system regulates rhythmic activity both by directly relayinginformation about the state of external stimulation and by circadian changes in sensitivity toincoming external signals.

Melatonin’s main role is to reflect environmental photoperiod via its secretion profileand can be considered a humoral signal of darkness. This function of melatonin persists

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regardless of whether the species are diurnal or nocturnal, making inferences for a directphysiological role of melatonin difficult. Endogenous melatonin may help to modulate circadianrhythmicity through feedback mechanisms via melatonin receptors on the SCN. It has beenproposed to influence sleep-wake timing and thermoregulation based mainly on extrapolationfrom studies of exogenous melatonin administration, although there is little direct evidence foran endogenous role in circadian regulation (Arendt, 1998b; Arendt, Middleton, Stone, &Skene, 1999; Czeisler, 1997; Korf, Schomerus, & Stehle, 1998). Melatonin also synchronizesthe responses of fetus and mother to environmental conditions (Menaker, 1997). Its most well-defined physiological role is the control of seasonal reproduction in some species, in which thecritical photoperiods controlling reproductive development and function are signalled humorallythrough the melatonin profile (Arendt, 1998b; Menaker, 1997; Wehr, 1991). Pinealectomyabolished such responses.

Melatonin is present in the gastrointestinal tract (Huether, 1993), retina (Gern &Ralph, 1979) ciliary body of the eye (Martin, Malina, Brennan, Hendrickson, & Lichter, 1992)and in the aqueous humour which bathes the iris of the eye (Abramson, Senft, Servodidio,Ellsworth, & Gamache, 1993; Martin et al., 1992). However, the principal source of circulatingmelatonin is its secretion by the pineal gland (Arendt, 1998b). As shown in Figure 3, one well-defined neural pathway that carries non-visual information about light extends from the SCN tothe pineal gland via a multisynaptic pathway with connections being made sequentially in theparaventricular hypothalamus, the upper thoracic intermediolateral cell column, and thesuperior cervical ganglion (Card, 1994; Klein et al., 1991; Klein et al., 1983; Moore & Lenn,1972; Pickard & Silverman, 1981). By way of this neuroanatomy, cycles of light and darknesswhich are perceived through the eyes entrain SCN neural activity which, in turn, entrains therhythmic production and secretion of melatonin from the pineal gland. Confirmation of thispathway in humans has been demonstrated in para- and tetraplegic patients (Zeitzer, Ayas,Shea, Brown, & Czeisler, 2000).

2.3.2 Acute light suppression

Light can have an acute suppressive effect on high levels of melatonin during the night. Thisacute light-induced suppression of nocturnal melatonin synthesis was first observed in rats(Klein & Weller, 1972) and has been used in numerous animal studies to help determine theneural and biochemical mechanisms of melatonin regulation (Brainard et al., 1994; Brainard,Rollag, & Hanifin, 1997; Bronstein, Jacobs, Haak, Neitz, & Lytle, 1987; Nelson & Takahashi,1991). In 1980, it was demonstrated that exposure of the eyes of normal human volunteers to2500 lux of white light during the night induced a strong decrease in circulating melatoninwithin one hour. In contrast, volunteers exposed to 500 lux of white light appeared to exhibitno significant melatonin suppression (Lewy, Wehr , Goodwin, Newsome, & Markey, 1980).

Early attempts to suppress melatonin in humans failed when investigators used typicalindoor light levels reported to be between 100 and 800 lux (Jimerson, Lynch, Post, Wurtman,& Bunney, 1977; Lynch et al., 1978; Vaughan et al., 1976; Wetterberg, 1978). At first, itappeared to take much more light to suppress melatonin in humans than is required forhuman vision. However, on closer examination, these findings were the result of poorexperimental controls (discussed below). Further evidence for differences between thesensitivities of the circadian and visual systems was shown in the demonstration of acutemelatonin suppression in three totally blind patients (Czeisler et al., 1995). At its extreme,under experimental conditions, dose-dependent melatonin suppression and phase shifts inhumans has been observed at much lower illuminance levels (Boivin, Duffy, Kronauer, &Czeisler, 1996; Brainard et al., 1988; Cajochen, Zeitzer, Ayas et al., 2000; Wright, Hughes,Kronauer, Dijk, & Czeisler, 2001). In one study, a single exposure to a simulated dawn signal(from 0,01 lx to 1000 lx over 90 min in the early morning) resulted in a small shift of circadianrhythm, as marked by the timing of dim light melatonin secretion the following night (Danilenkoet al., 2000).

Zeitzer, Dijk, Kronauer, Brown. and Czeisler (2000) found a non-linear relationship inwhich response to a single 6,5-hr episode in the early biological night of 100 lx resulted in 50%of the maximal response compared to 9000 lx, both in terms of circadian phase shifting andmelatonin secretion. It now appears that the circadian system is very sensitive to light

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exposure. However, the same study found that melatonin secretion and melatonin circadianphase-shifting responses do not show identical responses to interior light. Melatoninsuppression saturated (90% of maximal response) at 200 lx; melatonin circadian phaseshifting saturated at 550 lx. Thus, even modest changes in interior light exposures might haveprofound influences on circadian regulation and melatonin secretion, and light as dim ascandle light may be adequate to maintain entrainment to 24 hours in combination with weaknon-photic time cues (Wright et al., 2001). However, there remains much to be learned aboutthe effects of timing of exposure and the contrast of light exposure against background light.

Melatonin’s influence on sleep is complex (Arendt et al., 1999). The best sleep occurswhen core body temperature is dropping and melatonin production is rising (Arendt, 1998a);propensity for sleep (the "sleep gate") has been associated with onset of melatoninproduction. Blind individuals with free-running circadian rhythms (Lockley, Skene, Arendt etal., 1997) note the greatest sleep propensity around the peak of melatonin secretion and thetrough of core body temperature (Arendt, Middleton et al., 1999; Lockley, Skene, Butler, &Arendt, 1999; Lockley, Skene, Tabandeh et al., 1997; Sack, Lewy, Blood, Keith, & Nakagawa,1992). However, melatonin alone does not control sleep; it is possible to sleep out of phasewith melatonin secretion, and whether or not one experiences sleepiness following a dose ofexogenous melatonin depends on posture and activity (Arendt et al., 1999) and environmentallighting (Roberts, 2001).

Conversely, suppression of night-time melatonin secretion by bright light exposure iscoincident with increased self-reported alertness and increased cortical arousal (as assessedby electroencephalogaph [EEG] readings) (Badia, Myers, Boecker, & Culpepper, 1991;Cajochen, Krauchi, Danilenko, & Wirz-Justice, 1998; Cajochen et al., 2000; Daurat et al.,1993; French, Hannon, & Brainard, 1990), although a causal relation has not beenestablished. Cajochen et al. (2000) found that these effects followed the expected logarithmicdose-response curve. Two experiments found that bright light at night suppressed melatoninbut did not influence concurrent self-reported sleepiness (Dollins, Lynch, Wurtman, Deng, &Lieberman, 1993; Leproult, Reeth, Byrne, Sturis, & Cauter, 1997). Methodological differencesmight explain the null findings: In the case of Leproult et al. (1997), the onset times for lightexposure varied, which one would expect to add to the variability in sleepiness scoresimmediately following the exposure, whereas the initial sleep-wake states of the participants inDollins et al. (1993) appear not to have been controlled. In both cases the sensitivity of self-report measures of sleepiness would be reduced. (The effects of behavioural consequencesnot directly linked to melatonin are discussed below.)

2.3.3 Health and melatonin cycles

Wehr (1991; 1997; 1998; Wehr, Giesen, Moul, Turner, & Schwartz, 1995) published datasuggesting that urban environments offer biological darkness by day (in interiors with relativelylow illuminances) and unnatural brightness by night (electric lighting extending apparent daylength, producing apparently constant day length over the seasons), with unknown healthconsequences. One consequence of the apparently longer day is a decrease in the totalmelatonin release because of melatonin suppression during light exposure. Another possibilityis that daytime light exposures (which are relatively low) might influence subsequent melatoninrelease, as was observed in the laboratory by Wehr (1991). Total melatonin production isunknown for any population, but the possibility of systematic reductions, in quantity or cyclicamplitude, concerns some scientists.

For example, studies show that physiological nocturnal levels of melatonin inhibitsMCF-7 human breast cancer growth in vitro by suppressing the estrogen response pathway(Hill & Blask, 1988; Hill, Spriggs, Simon, Muraoka, & Blask, 1992; Molis, Walters, & Hill, 1993).There is also in vitro evidence that physiological nocturnal melatonin concentrations inhibit thegrowth of melanoma cells through mechanisms that remain uncertain (Hu, McCormick, &Roberts, 1998; Roberts, Wiechmann, & Hu, 2000), raising the possibility that reducedmelatonin levels in Western societies could contribute to both breast and skin cancerdevelopment.

Evidence is mounting that melatonin suppression might increase cancer risk, and inparticular, breast cancer (Hansen, 2001; Stevens, Wilson, & Anderson, 1997). The causal

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chain in this hypothesis is light exposure at night and the consequent suppression ofmelatonin. Among the indicators cited in the development of this hypothesis is the observationthat breast cancer incidence is highest in developed countries, where electric lighting isubiquitous (Brainard, Kavet, & Kheifets, 1999). Breast cancer is associated with high estrogenlevels. Although the nocturnal melatonin signal inhibits estrogen production in certainseasonally-breeding species, there is no evidence linking nocturnal melatonin levels with asuppression of estrogen production in humans (Reiter, 1998). Furthermore, no acute changesin circulating estrogen levels are associated with light-induced suppression of nocturnalmelatonin in healthy women at any menstrual cycle stage (Graham, Cook, Gerkovich, &Sastre, 2001). However, nocturnal melatonin concentrations block the ability of estrogen tostimulate the growth of MCF-7 human breast cancer cells in vitro (Hill et al., 1992). Dim light(0,25 lx) at night suppressed melatonin release by the pineal gland and increased tumourgrowth in a strain of rats with transplanted liver tumours (Dauchy, Blask, Sauer, Brainard, &Krause, 1999; Dauchy, Sauer, Blask, & Vaughan, 1997). Removing the pineal gland alsostimulated tumour growth (Blask et al., 1999). In addition, three epidemiological studies withdiffering methodologies have observed increased breast cancer risk among women who workat night or who have other light exposure at night (Davis, Mirick, & Stevens, 2001; Hansen,2001; Schernhammer et al., 2001), although these investigations could not entirely excludeother possible risk factors (e.g., sleep disruption, diet, other toxic exposures). Despite thislogical evidentiary sequence, much remains unknown, particularly as regards the intensity,spectrum and timing of light exposures that might lead to a higher incidence of breast andother cancers in humans.

2.4 Cortisol

Cortisol is secreted principally by the cortex of the adrenal gland, at the end of a sequence ofneurohormonal events. A current model for its circadian regulation holds that the SCN signalsto cells in the paraventricular nucleus (PVN) of the hypothalamus to secrete corticotropicreleasing hormone, which in turn stimulates the posterior pituitary to releaseadrenocorticotropic releasing hormone, which acts on the adrenal cortex to secrete cortisol(Buijs et al., 1998). Cortisol secretion shows a marked circadian pattern, peaking close tohabitual waketime (~08h00) and reaching its trough close to habitual bedtime (~midnight)(Figure 2), superimposed on a distinct pulsatile (ultradian) profile. The amplitude of this rhythmmight differ in people who report morning versus evening chronotypes (“larks” versus “owls”)(Bailey & Heitkemper, 2001), and for people with some mental disorders (AmericanPsychiatric Association, 1994). However, cortisol is also secreted in pulses over the day, andacutely in response to strong external stimulation (Baum & Grunberg, 1997). Cortisol’sprincipal functions are to regulate glucose production from protein and to facilitate fatmetabolism (Baum & Grunberg, 1997). Thus, its secretion in response to stressful eventshelps to release the energy needed to respond to threat. Its daily rhythm corresponds to theusual patterns of daily activity in humans.

Because of its association to sleep-wake cycles and activity, and strong circadianrhythmicity, cortisol has been a target of photobiologists interested in determining whichcircadian rhythms respond to light. Two studies have found that morning light exposure caninfluence cortisol secretion, whereas evening light has no effect on cortisol levels (Lemmer etal., 1994; Scheer & Buijs, 1999). Lemmer et al. (1994) found that six days of bright lightexposure in the morning, before the daily cortisol peak, advanced the phase of the cortisolrhythm, whereas six days of bright light exposure in the evening, before the daily cortisolnadir, had no effect on cortisol circadian rhythms. Scheer and Buijs (Scheer & Buijs, 1999)found an acute increase in salivary cortisol following morning light exposure, but no acuteeffect following evening light exposure.

2.5 Other biological functions

Many biological functions show circadian rhythms and are the targets of photobiologicalresearch, although melatonin, core body temperature, and (to a lesser extent) cortisoldominate research efforts at present, as they are considered to be the strongest endogenousoutputs or markers of the circadian system. Control of the circadian rhythm of heart rate isamong the other functions actively under investigation. There exists a circadian rhythm for

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heart rate independent of sleep, in which heart rate peaks around midday and is lowestaround midnight (Scheer, van Doornen, & Buijs, 1999), with an amplitude of approximately 6,5beats per minute. Heart rate increased in a dose-dependent manner in response to acutebright light exposure during the night and early morning, but not during the day. This pattern ofresults suggests that one pathway for influencing heart rate is via the nonvisual receptorpathway and the SCN.

Reproductive hormones such as prolactin and luteinizing hormone also showcircadian rhythms (Waldstreicher et al., 1996; Wehr, 1998). Studies of these hormones’circadian patterns have been complicated by the strong influence of sleep on their secretion(Czeisler & Klerman, 1999) and by the fact that these hormones differ in level and secretionpattern between the sexes. The seasonal patterns that have been observed in thesehormones are believed to be responses to changes in day length; both men and womenrespond to changes in apparent day length with changes in both the amplitude and pattern ofhormone production (Wehr, 1998).

A complete catalogue of all known SCN-controlled circadian rhythms is beyond thescope of this report. The inter-relationships between hormones and neurotransmitters, andtheir circadian, infradian, and circannual rhythms, are likely to be the target of future reports asour knowledge increases.

2.6 Photoimmune responses

Among the physiological processes that the pineal gland mediates, immune response hasattracted attention because of its obvious relation to disease processes. However, thesemechanisms are poorly understood as yet, and there is recognition that the neurohormonalmechanisms involved are complex and interactive (Brainard, Hanifin, Barker, Sanford, &Stetson, 2001; Maestroni, 1999; Maestroni, 1993; Roberts, 1995; Roberts, 2000). Theoperation of the immune system shows its own circadian rhythms (Levi, Canon, Dipalma,Florentin, & Misset, 1991), with parameters relating to fighting the initial exposure to apathogen being more active when the organism is active (i.e., during the day for diurnalanimals, and nocturnally for animals active at night), and more energetic infection-fightingmechanisms being more active when the animal is at rest (Plytycz & Seljelid, 1997).Circannual rhythms of immunity are also known; for instance, seasonal changes in immunefunction might be a marker for Seasonal Affective Disorder (Avissar et al., 1999). As ourknowledge of these rhythms expands, it might become possible to optimise the effectivenessof drug administration and medical treatment by linking it to circadian or circannual phasestates, although at present such protocols are in their infancy.

Melatonin, produced by the pineal gland, influences the activity of several componentsof the immune system (Cardinali, Brusco, Cutrera, Castrillon, & Esquifino, 1999; Maestroni,1993; Molinero, Soutto, Benot, Hmadcha, & Guerrero, 2000; Park & Tokura, 1999). Forexample, following exposure to 5000 lx of white light during the day, night-time melatoninsecretion increased in comparison to secretion levels following 200 lx during the day (thebright light exposure, in effect, increased the amplitude of the circadian rhythm) (Park &Tokura, 1999). During the daytime hours, secretion of salivary immunoglobulin A, an antibody,increased in bright light in comparison to dim. The overall melatonin secretion correlatedhighly with the overall salivary immunoglobulin A secretion. Circadian rhythms, apparentlymediated by melatonin, were observed to influence blood concentrations of some cytokines,which are chemicals released by immune cells that regulate immune cell interactions (Lissoni,Rovelli, Brivio, Brivio, & Fumagalli, 1998). Melatonin activity on the thymus gland also appearsto contribute to the regulation of immune functions (Molinero et al., 2000).

One challenge to this area of research is the separation between correlation andcausation. Current knowledge offers few certainties but this: Researchers working in thisrealm will continue to provide insight into this complex system for many years to come.

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3. OCULAR ANATOMY AND PHYSIOLOGY

3.1 The visual system

Scientists are generally agreed that separate systems process light information for vision andlight detection for co-ordinating physiological responses to environmental conditions (Devlin &Kay, 2001; Foster, 1998; Moore, Speh, & Card, 1995). However, the two systems share acommon anatomical starting point: the eye. The eye is a complex organ consisting of opticalstructures for admitting and focusing light onto the receptor tissue, the retina (Figure 4).

Detailed descriptions of the visual system are available from a lighting perspective inseveral sources (e.g., Illuminating Engineering Society of North America (IESNA), 2000). Lightfalling on the retina is detected by two types of visual photoreceptors, rods and cones. Cones,which predominate at the centre of the retina (the fovea), are responsible for the detection offine detail and colour vision. They are most sensitive at relatively high light levels. The overallspectral sensitivity of cones leads to the V(λ) curve, established by the CIE as the photopicsensitivity function (Figure 5) (CIE, 1978). Rods are most numerous in the peripheral areas ofthe retina. They are less able to detect fine detail but are most active at low light levels. Therod spectral sensitivity function is known as V’(λ), the scotopic sensitivity function (Figure 5)(CIE, 1978). Both types of photoreceptors contain photopigments that convert light energy toelectrochemical signals. Photoreceptor cells provide input to bipolar and ganglion cells, whichsum information from overlapping circular receptive fields before transmitting the information,through the optic nerve, to the visual cortex.

Figure 4. A section of the eye, showing major structures. Source: IESNA Lighting Handbook,9th Edition, 2000, courtesy of the Illuminating Engineering Society of North America.

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Figure 5. The photopic V(λ) and scotopic V’(λ) visual sensitivity functions. Source: IESNALighting Handbook, 9th Edition, 2000, courtesy of the Illuminating Engineering Society ofNorth America.

3.2 Nonvisual photoperception

3.2.1 Location of nonvisual photoreceptors

There is considerable evidence from human and animal studies that the biological,behavioural and therapeutic effects of light apart from vision are mediated via aphotoreceptive mechanism in the eye as opposed to a photoreceptive mechanism in the skinor some other part of the body (Aschoff, 1981; Binkley, 1990; Klein et al., 1991; Wehr,Skwerer, Jacobsen, Sack, & Rosenthal, 1987; Wetterberg, 1993). Nonetheless, the possibilitythat mammals might also exhibit nonocular photodetection remains controversial. One studyfound that congenitally anophthalmic rats exhibited entrained circadian rhythms of pineal glandactivity, which suggests a non-ocular mechanism of some kind (Jagota, Olcese, Rao, &Gupta, 1999). Mole rats also show this ability (Pevet, Heth, Hiam, & Nevo, 1984). In somehumans with complete visual blindness, melatonin suppression can be induced by exposingthe eyes to bright white light (Czeisler et al., 1995). In that study, blind subjects with loss ofpupillary reflex, no conscious perception of the light stimuli, and no outer retinal functioning asdetermined by electroretinographic testing, still exhibited neuroendocrine sensitivity to light.

Campbell and Murphy (1998) elicited great interest with observations that lightexposure to the popliteal region (behind the knee) caused circadian phase shifts. However,this finding has been challenged on methodological and theoretical grounds (Czeisler &Klerman, 1999; Foster, 1998), and has failed attempts at independent replication (Eastman,Martin, & Hebert, 2000; Hebert, Martin, & Eastman, 1999; Koorengevel et al., 2001; Lockley etal., 1998). In a comparison of blind subjects with some light perception, no light perception, orwhose eyes had been removed altogether (Skene, Lockley, Thapan, & Arendt, 1999), thesubjects without light perception had abnormal circadian rhythms compared to those who hadsome light perception, and those without eyes had free-running circadian rhythms formelatonin and cortisol. One hypothesis that can be ruled out is an influence of internal mentalrepresentations of light on circadian rhythms (Byrne, Rollag, Hanifin, Reed, & Brainard, 2000).

3.2.2 Ocular photoreceptors

Data from animal and human studies raise the possibility that neither the rods nor the conesused for vision participate in regulating the circadian and neuroendocrine systems. Forexample, rats with total or near-total destruction of retinal photoreceptors due to prolongedconstant light exposure still entrain their melatonin rhythms normally to the ambient light:dark

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cycle and exhibit acute light-induced suppression of nocturnal melatonin (Webb, Champney,Lewinski, & Reiter, 1985). Additional studies showed that retinally degenerate mice (rd/rd)exhibit normal circadian responses to 515 nm light pulses despite a nearly total loss ofclassical visual photoreceptors (Argamaso et al., 1995; Foster et al., 1993; Foster et al.,1991). Mice lacking either rod or cone photodetectors show circadian phase shifts in responseto bright light (Freedman et al., 1999).

One way to determine the nature of the photoreceptors involved in circadian andneuroendocrine regulation is to study whether a deficiency in the colour perceptual systemaffects light-mediated melatonin suppression. Volunteers were screened for colour visiondefects using the Ishihara, Farnsworth-Munsell, and Nagel anomaloscope tests, and thosewith deficiencies were compared to volunteers with normal colour vision (Ruberg et al., 1996).Colour vision deficient subjects had either protanopia (functionally lacking the "red" conepigment), or deuteranopia (functionally lacking the "green" cone pigment), or they weredeuteranomalous (having a deficiency in the "green" cone system) or unspecified indeficiency. Light suppressed melatonin secretion both in subjects with normal colour visionand subjects with colour vision deficiencies, with no significant difference in the degree ofmelatonin suppression between the two groups. These findings suggest that a normaltrichromatic photopic system is not necessary for light regulation of the human pineal gland.Furthermore, in humans with normal colour vision, monochromatic light at 555 nm is not aseffective at melatonin suppression as 505 nm, as would be expected if the three-comephotopic visual system were the mediator of this response (Brainard et al., 2001b).

Although it is not known which photoreceptors and photopigments transduce lightstimuli for the non-visual biological and therapeutic effects in humans, evidence for theexistence of a novel non-rod, non-cone photoreceptive system is mounting. Nearly allresearchers acknowledge that the peak sensitivity of the circadian and neuroendocrinesystems is in the blue-green portion of the visible spectrum (Brainard et al., 1988; Brainard,Richardson, King, & Reiter, 1984; Bronstein et al., 1987; Foster et al., 1993; Nelson &Takahashi, 1991; Podolin, Rollag, & Brainard, 1987; Takahashi, DeCoursey, Bauman, &Menaker, 1984; Thiele & Meissl, 1987). In Siberian hamsters, 15-minute pulses of near-ultraviolet radiation as short as 320 nm regulated photoperiodic reproductive and immuneresponses, as did visible light at 500 nm. However, visible light at 750 nm did not affect theseresponses (Brainard et al., 2001). This is consistent with the pattern of evidence suggestingthat the photoreceptors involved in nonvisual processing are not the same as the visualsystem photoreceptors. Some researchers have called this the "non-image-forming"photoreceptive system (e.g., Hattar, Liao, Takao, Berson, & Yau, 2002).

Two independent teams have proposed action spectra for melatonin suppression inhumans (Brainard et al., 2001a; Thapan, Arendt, & Skene, 2001). The spectra are similar toone another but do not correspond to either the photopic or scotopic sensitivity curves (seeFigure 6). The action spectrum data suggest that the photoreceptor is a vitamin A-basedopsin molecule (Brainard et al., 2001a; Thapan et al., 2001).

Melanopsin, a novel putative photopigment, has been localised to very few widelydistributed retinal ganglion cells that are identical in number and distribution to ganglion cellsthat project to the suprachiasmatic nucleus (SCN) (Provencio et al., 2000; von Schantz,Provencio, & Foster, 2000). The ganglion cells that project to the SCN have been shown to bedirectly photosensitive (Berson, Dunn, & Takao, 2002). Berson et al. (2002) observed anaction spectrum with a peak at 484 nm for their rat ganglion cells. Hattar et al. (2002)demonstrated that melanopsin is present in these photosensitive retinal ganglion cells in therat, and that these retinal ganglion cells project to the SCN in the mouse. Taken together, thedata suggest that melanopsin-containing cells form the basis for the transmission ofinformation about external light conditions to the SCN. The generation of melanopsin-null micewill allow investigators to probe melanopsin’s role in nonvisual photoreception.

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Figure 6. Two proposed action spectra for melatonin suppression.

6A. Results from Brainard et al. (2001a). The circles are the obtained data for normalisedmelatonin suppression by wavelength. The curve is the best-fit template for vitamin A1

retinaldehyde pigment with predicted peak spectral response at 464 nm, which shows a verygood fit to the data, R2=0,91. © 2001 by the Society for Neuroscience, courtesy of the Societyfor Neuroscience and the authors.

6B. Results from Thapan et al. (2001). The circles are obtained data for log relative melatoninsuppression, corrected for lens filtering, showing good agreement (R2=0,74) with an opsintemplate having a peak at 459 nm. © 2001 by The Physiological Society, courtesy of ThePhysiological Society and the authors.

It is also possible that vitamin B2-based cryptochromes mediate circadianphotoreception in mammals, as they are known to do in plants and insects (Devlin & Kay,1999). Cryptochromes have also been located in ganglion cells (Miyamoto & Sancar, 1998),and mice deficient in cryptochrome CRY2 show abnormalities in circadian rhythm entrainment(Thresher et al., 1998). The role of cryptochromes in photoreception remains controversial.Some authors have suggested that their role is as a regulator, but not a photoreceptor (Griffin,Staknis, & Weitz, 1999; von Schantz et al., 2000). This argument is strengthened by theaction spectrum data, which is not consistent with known cryptochrome absorption spectra.Others have argued that cryptochromes might act in both roles, as photoreceptors and ascircadian regulators (Devlin & Kay, 2001; Horst et al., 1999), perhaps in addition to otherphotoreceptors.

In addition to the intrinsic importance of understanding the physiology of nonvisualphotodetection, and its possible consequences for the design or selection of light sources forlight treatments, the receptor mechanism has important implications for light measurementand research design. These are discussed below.

3.2.3 Retinal location of nonvisual photoreceptors

The location of the nonvisual photoreceptors is also under debate. Some argue that nonvisualphotoperception is stronger in the nasal area of the retina than the lateral area (Visser,Beersma, & Daan, 1999); others have observed that the upper visual field is more sensitivethan the lower (Lasko, Kripke, & Elliot, 1999). Others have found that the system involves veryfew ganglion cells that are widely distributed across the retina (Card, 2000; Moore et al., 1995;Provencio, Cooper, & Foster, 1998). This would be consistent with early evidence that centraland peripheral light exposure are equally effective at suppressing melatonin secretion (Adler,Kripke, Loving, & Berga, 1992). Resolution of this issue could have implications for thedevelopment of devices to target delivery of biologically-active light.

6A. 6B.

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3.3 Circadian rhythms of ocular sensitivity

Separately from the research programs into the secretion and functions of pineal melatonin,investigators have also observed diurnal rhythms of melatonin release in the eye, where itappears in the retina (Gern & Ralph, 1979; Tosini, 2000) and ciliary body of the eye (Martin etal., 1992) and in the aqueous humour (Martin et al., 1992). Circadian rhythms of ocularfunctions have also been observed (Tuunainen, Kripke, Cress, & Youngstedt, 2001). As withpineal melatonin, secretion increases in darkness and decreases with light exposure. Thefunctions of ocular melatonin are as yet unknown, but appear to be interconnected to theactions of other neurotransmitters, particularly dopamine (Tosini, 2000).

One intriguing possibility is that melatonin might influence retinal sensitivity to light.Melatonin increases the degree of light-induced photoreceptor cell death in albino rats(Wiechmann & O’Steen, 1992), Also, a melatonin receptor antagonist protects photoreceptorsfrom such light-induced damage, thus demonstrating that the effect of melatonin is mediatedthrough a retinal melatonin receptor (Sugawara, Sieving, Iuvone, & Bush, 1998). Thus theremight be an interplay between the visual and nonvisual photoreceptor systems.

Melatonin also influences intraocular pressure (McLaren, Brubaker, & FitzSimon,1996). The discovery of a melatonin receptor in human uveal melanocytes (Roberts et al.,2000) suggests that the control of the circadian changes in intraocular pressure may bedirected, as least in part, by the presence and absence of melatonin in the aqueous humor ofthe eye (Martin et al., 1992).

3.4 Age and ocular sensitivity

Age-related changes in vision are well known (Dillon, 1991). The crystalline lens thickens andbecomes more opaque, so that accommodative power is reduced and less light reaches theretina (cf., Illuminating Engineering Society of North America (IESNA), 2000). In addition, thelens transmittance changes selectively across wavelengths, becoming less able to transmitshort wavelengths (Brainard et al., 1997) (Figure 7). Thus, not only is less light transmitted,but the loss is greatest in what appears to be the area of high circadian photoreceptorsensitivity. This might account in part for age-related reductions in the amplitude of circadianrhythms (Arendt, 1998a).

Figure 7. Average human lens transmittance by wavelength, in relation to age. Values areexpressed as a percentage of the 560 nm point for newborns. Source: Brainard et al. (1997),courtesy of the authors.

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4. BEHAVIOURAL EFFECTS IN HEALTHY PEOPLE

4.1 Circadian rhythms of behaviour

Daily rhythms are observed in behaviour as well as in the physiological functions that underliethem. Performance rhythms have been recognised for nearly a century, and early studiesaimed at identifying the best time of day to teach academic subjects (Carrier & Monk, 2000).Carrier and Monk reviewed the literature, observing that the study of such rhythms over theworking day has been complicated by the need to separate endogenous rhythms from thehomeostatic effects of the time since waking. Moreover, many studies find that effects differfor different tasks. Under conditions of forced desynchrony, when subjects are not sleep-deprived but are tested at all circadian periods, there appears to be a consistency between thedaily temperature rhythm (which is lowest in the early morning and peaks in the lateafternoon). However, this pattern is modified by the effects of waking time, personality, andage, so that to observe this pattern requires extensive experimental controls.

There also exists an ultradian rhythm of performance, known as the "post-lunch dip"(Carrier & Monk, 2000), in which performance declines in the early afternoon and sleeppropensity increases. However, not all individuals show this phenomenon; morningness-eveningness has been suggested as one potent individual difference, with morning typesshowing a larger post-lunch dip than evening types (Carrier & Monk, 2000).

Mood, as well as activity, shows circadian variation, but such effects are difficult todetect because of the stronger effects of activity and social setting (Stone, Smyth, Pickering,& Schwartz, 1996). Among the mood constructs that most appear to show circadian patternsare feeling rushed, tired, and sad. Feeling rushed tended to decline over the waking day;feeling tired and sad tended to increase. Stone et al. (1996) speculated that this effect mightrelate to known physiological cycles, such as cortisol rhythms, but to date there appear to beno interdisciplinary attempts between psychologists and physiologists to examine thisquestion. Many of the same considerations as discussed with reference to the performancecycle data (Carrier & Monk, 2000) would apply here.

4.2 Effects of daytime light exposure

4.2.1 Activation and arousal

Waking is characterized by an increase in activity in the ascending reticular activating system,a diffuse section of the midbrain with connections to the thalamus and hypothalamus (Kalat,1984). The role of light in entraining sleep-wake cycles was revealed in part by studiesshowing changes in the circadian phase of temperature and hormone release (Lavie, 2001).Bright light exposure just after the morning temperature nadir shows a strong melatoninsuppression response and can advance the circadian phase of melatonin (so that the followingnight’s peak will occur earlier); an evening exposure can delay the circadian phase (Czeisler &Klerman, 1999; Reppert & Weaver, 2001). Light exposure during the day, however, does notadjust the circadian phase, because the clock mechanism is sensitive only a specified pointsin the cycle (Gillette & Tischkau, 1999). In addition, melatonin has a feedback effect on theSCN that appears to modulate the activity of the circadian clock (Gillette & Tischkau, 1999).

Arousal is a general state of mental and physical activation in response to externalstimulation, generally involving increased sympathetic nervous system activity andsubjectively reported intensity of emotional response (Kalat, 1984). Arousal is popularly usedas an explanatory, intervening variable, it is not a unidimensional construct (Lacey, 1984).Inferences about arousal require that simultaneous observations of all the elements in thesystem occur as predicted (Blascovich & Kelsey, 1990; Venables, 1984). Physiologicalindicators include heart rate, skin conductance, muscle tension, and endocrine hormonerelease (e.g., increased cortisol levels). External stimulation influences arousal, but in complexways depending on the state of the organism and the level of all the stimuli. The effects ofvarious stimuli are not additive (Wilkinson, 1969).

The selective circadian sensitivity to light exposure is at odds with a commonassumption about light: that more light always increases activation levels. It probably explains,

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however, the difficulty in observing the expected effects. Badia et al. (1991), for example,found that bright light exposure at night had behavioural and physiological effects; there wereno differences in body temperature, EEG readings, or psychomotor and cognitive taskperformance, between bright and dim light exposures (5000 lx and 50 lx) in 90-min blocksduring daytime. Küller and Wetterberg (1993) hypothesized (as have many researchers) thatincreased room illuminance would increase physiological arousal. Their participantsexperienced 450 or 1700 lx mean horizontal illuminance, from one of two lamp types, for a dayat a time. Under the higher illuminance they observed some effects in EEG readings, but notthe consistent pattern that would provide a clear result: There were lower delta rhythms(indicating less sleep propensity), but no effects on theta rhythms, which characterise a stateof sleepiness. There were inconsistent interactions of lamp type x illuminance x hemisphere(left and right) in alpha rhythms, and a contrary interaction for beta rhythms. Heart rate,cortisol, and melatonin measurements showed no effects of lamp type or illuminance.

Begemann, Beld and Tenner (1997) collected illuminance level and colourtemperature preferences in relation to time of day and external weather conditions.Participants in their study added approximately 1000 lx of electric light to daylight in the rangeof 1000-4000 lx on the desk surface. They speculated that the changes they observed inilluminance preferences over the course of the working day (small peaks in the morning andearly afternoon) relate to differences in alertness. That is, that individuals prefer higherilluminances at the time of day when the circadian cycle dips, so that illuminance maintains anacceptable alertness level. They speculated that this could be an attempt to counteract thepost-lunch dip with an acute increase in light exposure, but lacked the physiological data totest this hypothesis. To date, there appear to have been no attempts to replicate this effectwith a complete battery of measures.

Grünberger, Linzmayer, Dietzel, and Saletu (1993) exposed participants to thirty-minute periods of 2500 lx or 500 lx light on four occasions over an 8-hour day. Theirphysiological measurements were limited to visual functions (pupil response) andelectrodermal measures. They interpreted the pattern of findings as indicative of increasedarousal in response to bright light, particularly around midday and shortly after. It is not clearthat the changes in visual functions were not predictable responses to visual stimulation.Moreover, there were statistically significant effects of light exposure on fewer than half of thephysiological measures, and these effects were small.

4.2.2 Performance

Arousal is a popular explanatory concept in psychology, often used imprecisely as a symbolicconstruct rather than measured physiologically (Blascovich & Kelsey, 1990). The term is oftenused to refer to the state of activation of an organism, although sometimes an acute responseto a stimulus is to be inferred. This lack of precision is among the problems with the literaturein this area.

Arousal theory holds that there is an inverted-U function between arousal levels andbehaviours, with an optimal arousal level for each behaviour (Yerkes & Dodson, 1908). Fortask performance, the curve is believed to shift up for simple tasks (that is, the optimal arousallevel is higher if the task is easier) (Kantowitz & Sorkin, 1983; Landy, 1985). Thus, even ifmore light were better light, the best light (in arousal terms) would depend on the task. Twodemonstrations are needed to support this theory: first, that higher illuminance increasesarousal; and second, that the increased arousal leads to predictable changes in taskperformance following the inverted-U function. However, arousal research in general suffersfrom a logical flaw in that the optimal arousal levels for a given task are defined post hoc aswhatever level led to the best performance of that task. This prevents a test of the hypothesisthat the achieved arousal level is equal to the optimal arousal level.

As applied to lighting, the general assumption has always been that more light willincrease arousal and that this increase will improve performance; consistent with this belief,illuminance recommendations increased throughout the 20th century, until energy became adominant issue in the 1970s (Mills & Borg, 1999). Evidence is weak for illuminance leveleffects on generalised arousal, and the research evidence for illuminance effects on taskperformance is mixed (Veitch, 2001). Part of the problem is that many variables influence

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performance of any task, so that very sensitive experimental designs are required to detect aneffect of lighting beyond simple visual performance effects. In addition, one needs more thantwo points (dim and bright) to determine whether the outcomes follow the curvilinear pathpredicted by arousal theory. If arousal is the intervening mechanism, then one would expectthe illuminance-performance relationship to follow the inverted-U function, and that lowerilluminances would be favoured for more complex tasks. Overall, the literature does notsupport this prediction (Veitch, 2001).

The use of different measures of arousal in each study adds to the interpretativedifficulty of this pattern of results; few researchers combine a set of physiological measureswith subjective and objective behavioural measures. In addition, the range of illuminances hasvaried widely from one study to another. However, meta-analytic techniques are a recentstatistical development that allow the results of several independent research studies to bequantitatively and systematically combined to reach a general conclusion about a specifichypothesis. Gifford, Hine, and Veitch (1997) applied this technique to the literature onilluminance effects on office task performance. The meta-analysis was limited by the quality ofthe published reports on this topic: many investigations that were candidates could not beincluded because they included too few statistical details to allow effect sizes to be calculated(only 11 studies were found that provided all necessary information). Overall, Gifford et al.(1997) found that contrasts between low (average 70 lx) and medium (average 486 lx)illuminance levels did not produce significant effects on task performance; however, contrastsbetween low and high illuminance (average 1962 lx) produced a (statistically significant)average correlation of 0,25 between illuminance and task performance. Closer analysisrevealed that this relationship might be moderated by the adaptation time. Studies thatallowed more than 15 minutes to adapt to the new lighting level showed a smaller relationshipbetween illuminance and task performance. Thus, it is likely that any relationship betweenthese variables is transitory. People adapt to new lighting levels, and can perform well over abroad range.

4.2.3 Mood and comfort

In the industrialised world, total daily light exposure (from all sources) is low (Espiritu et al.,1994; Koller, Kundi, Stidl, Zidek, & Haider, 1993). Espiritu et al. found that the median personspent 4% of each 24 hr in illumination greater than 1000 lx, and more than 50% of the time inilluminance levels from 0,1 to 100 lx (an additional 38,6% of the time was below 0,1 lx,consistent with sleeping, driving at night, etc.). Their results suggested that inadequate lightexposure is associated with depressed mood, although they were unable to demonstrate aclear causal link (Espiritu et al., 1994; Kripke et al., 1994; Wehr, 1991). In addition, peoplebelieve strongly that natural daylight is more conducive to good health (Veitch & Gifford, 1996;Veitch, Hine, & Gifford, 1993).

Laboratory and field evidences points to a possible effect of light exposure on mood.In a 24-hour constant routine, Daurat et al. (1993) found that participants reported betterdaytime mood under 2000 lx than under 300 lx. Partonen and Lönnqvist (2000) enrolledhealthy Finnish volunteers in a test of bright light exposure (using light boxes commonly usedfor therapy) during the winter months, and observed increases in vitality and mood. Vitalityand mood also increased when people participated in an exercise programme (1 hr 2-3 timesper week, for 8 weeks) under bright light (2500 - 4000 lx), as compared to a relaxationprogramme or to an exercise program under ordinary light levels (400 - 600 lx) (Partonen,Leppämäki, Hurme, & Lönnqvist, 1998). Workplace use of a light box to increase lightexposure for two hours in either the morning or evening successfully improved mood, energyand alertness ratings of a group of people with sub-syndromal Seasonal Affective Disorder(Avery, Kizer, Bolte, & Hellekson, 2001). These findings point to possibilities for application toarchitectural lighting, a topic we discuss below.

If higher illuminance does improve mood, people do not uniformly self-select it. Thereis contradictory evidence concerning preferred illuminance levels in interiors (Veitch, 2001),with some investigators finding higher levels (1000 lx and greater) being more desirable(Begemann et al., 1997; Collins et al., 1999) and others finding that lower levels, consistentwith codes and standards, are preferred (Veitch & Newsham, 2000). Integrating the literature

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in this area is difficult because illuminance preferences are linked to tasks, which differ widelyacross studies and historical time. If, as appears likely, individual differences moderate theeffects of light on human behaviour and physiology (Bailey & Heitkemper, 2001; Begemann etal., 1997; Carrier & Monk, 2000; Küller & Laike, 1998), this might explain the variability infindings, but it will make the determination of optimal general lighting solutions more difficult.

4.3 Effects of night-time light exposure

4.3.1 Alertness

Overnight protocols, with light exposure during times when people are normally asleep, havebeen the predominant tool to study the effects of light on circadian rhythms, particularlymelatonin secretion. Photobiologists often use multiple measures to study the effects of lightexposure, and these are the basis for much of what is known about melatonin's effects onactivation, discussed above. Similarly, in studies simulating night work settings, bright lightexposure at night acutely suppressed melatonin secretion, and increased self-reportedalertness (or decreased self-reported sleepiness) (Bernecker et al., 1994; Boyce, Beckstead,Eklund, Strobel, & Rea, 1997; Daurat et al., 1993).

4.3.2 Performance

Several investigations have found that bright light during overnight simulated work sessionscan improve performance in comparison to dim light. These findings have implications for thedesign of settings where night work is a necessity. In one study, healthy young malevolunteers stayed awake and worked continuously at a computer for 30 hours, taking onlyshort breaks to eat or go to the bathroom (French et al., 1990). When working under 3000 luxof white fluorescent light during 18:00 to 06:00 hours (6:00 PM to 6:00 AM) the volunteersexhibited significantly improved behavioural and mental performance (reaction time,mathematical ability, complex problem solving) compared to their own performance on aseparate occasion under 100 lux. There were also significant differences in the bodytemperatures and blood hormone levels in these volunteers under the bright versus dim lightcondition (Brainard, French et al., 1991). Similarly, Badia, Myers, Boecker and Culpepper(1991) observed that bright light exposure overnight could improve performance onpsychomotor and simple cognitive tasks in comparison to dim light (5000 vs 50 lx). Daurat etal. (1993) found that participants in a 24-hr constant routine of bright (2000 lx) or dim light(300 lx) performed better on both simple and complex cognitive tasks.

Performance effects of night-time bright light exposure are, however, difficult todetect, requiring careful attention to research design and statistical analysis. In twoexperiments, male participants have shown melatonin suppression in response to bright lightexposure, but no improvements in clerical task performance associated with light exposure(Dollins et al., 1993; Leproult et al., 1997). One reason for these null findings on taskperformance could be that the tasks were too easy to be sufficiently affected by a short periodof sleep deprivation, or improved by light exposure during the sleepless night.

One study systematically examined task complexity, in a procedure designed to mimicthe fast-rotating 3-night shift cycle used in industry. Boyce, Beckstead, Eklund, Strobel, andRea (1997) examined the effects of using a daylight-simulating skylight in a mock office overthe night shift. When the skylight was either at a constant 2800 lx and 4050 K correlatedcolour temperature, or followed a slow ramp from 2800 lx to 200 lx and 4050 K to 2800 K,(simulating midday to dusk changes over 8 hours), male participants showed improvedperformance on complex cognitive tasks, but not on simple tasks. Perhaps simple tasks canbe performed adequately despite overnight sleepiness (without bright light exposure);alternatively, if one accepts arousal theory, perhaps bright light exposure shifts arousal pastthe optimal level for simple tasks, so that performance on these tasks, at night, is at the samelevel under either bright or dim light. Further investigation of this question is required;additionally, the optimal degree of light exposures for various jobs and their specific tasksremains unknown.

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4.3.2 Mood

Interestingly, bright light overnight does not appear to have the same effect on mood as duringthe day. Fewer investigators have included mood measures among their dependentmeasures, but in these instances there were no immediate benefits of bright light overnight onmood ratings of pleasantness or positive affect (Boyce et al., 1997; Daurat et al., 1993). It ispossible that in these experimental settings, being in a regimented routine overnight has itsown effects on mood that are unlikely to be altered by a short-term light exposure.

One team has investigated the effects of light dose on mood in permanent night shiftworkers. Koller et al. (1993) observed that the effect of a higher overall light dose on thecircadian rhythm in mood differed for day- and night-shift workers. For day-shift workers, thosewith higher light doses showed a peak in mood later in the morning, instead of early in themorning (a positive correlation); for night-shift workers, higher light doses were associatedwith peak mood in the late afternoon instead of the late evening (a negative correlation).However, the report did not discuss the absolute levels of the mood scores in either group.

4.4 Circadian phase shifting

4.4.1 Jet lag

In 1931, a pioneer named Wiley Post was the first to fly an airplane around the planet. Heaccomplished this feat in an eight day eastward flight (Winfree, 1987). He was also the first todescribe a phenomenon now familiar to many modern transcontinental travellers: jet lag.Today, jet lag is understood as a condition which results from rapid transport over several timezones. Jet travel over 5 or more time zones appears to cause greater problems than shorterflights. While readjusting the biological clock to a new geophysical time zone, many peopleexperience uncomfortable symptoms such as daytime sleepiness, night-time insomnia, gastro-intestinal distress, irritability, mild depression and confusion (Boulos et al., 1995; Winget,DeRoshia, Markley, & Holley, 1984). Such symptoms can pose serious problems for thebusiness traveller and can certainly limit the enjoyment of a vacation for the leisure traveller.Depending on the direction of travel (eastward or westward) and the number of time zonescrossed (5 to 11), the typical human circadian system re-adjusts to such a challenge withinthree to twelve days (Boulos et al., 1995).

Studies indicate that properly timed bright light exposure (and bright light avoidance)may prevent or ameliorate jet lag (Boulos et al., 1995; Daan & Lewy, 1984; Wever, 1985).These initial findings suggest that light can be a useful tool for quickly resetting the traveller’sbiological clock and overcoming some of the problems associated with jet travel. There are noset recommendations concerning how best to use light for this modern malady (Society forLight Treatment and Biological Rhythms, 1991), but some guidelines have emerged, andsoftware to facilitate the timing of light exposure has been developed (Boulos et al., 1995;Houpt, Boulos, & Moore-Ede, 1996).

Adjusting the circadian rhythm to a new time zone requires either an advance (afteran eastward flight) or a delay (after a westward flight, or after an eastward flight of more than 9hours) of the cycle (Waterhouse, 1999). Because the circadian clock is more easily delayedthan advanced (Eastman & Martin, 1999), most people find it easier to adapt after a westwardflight than an eastward one. Advancing the circadian rhythm can be accomplished by brightlight exposure during the hours after the minimum body temperature and by avoiding light inthe hours before the temperature minimum (Czeisler & Klerman, 1999; Eastman & Martin,1999; Waterhouse, 1999), which might be achieved by bright light exposure in the morning atthe destination after eastward travel (Chesson et al., 1999). Delay in the circadian rhythmrequires bright light exposure in the hours before the temperature minimum, and lightavoidance in the hours after the minimum body temperature (Czeisler & Klerman, 1999;Eastman & Martin, 1999; Waterhouse, 1999), using bright light treatment in the evening at thedestination following westward travel (Chesson et al., 1999). From a practical standpoint thesegeneral guidelines are difficult to implement: Travellers generally have little control over theavailability of light or darkness at the critical times, which might conflict with the requirementsof the itinerary (e.g., during stopovers, or while waiting to board the aircraft). More seriously, it

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is difficult to assess circadian phase (Arendt, 1999), making it difficult for an individual tocorrectly identify the appropriate times for light and dark exposure.

Another approach to modifying circadian rhythms is the administration of exogenousmelatonin, usually orally. Arendt et al. (1999) reviewed the trials where this had beenattempted and reported that melatonin can successfully shift circadian rhythms, but that thereare many unanswered questions. Individual responses differ widely, so that it is impossible atpresent to recommend an optimal dose; moreover, there is little data concerning possible sideeffects or adverse interactions with other medications. Simple clinical recommendations for itsuse await advances in our understanding of its many physiological functions and itspharmacokinetics.

4.4.2 Shift work

Shift workers, like intercontinental travellers, also suddenly change their sleep and wakingtimes. Currently, it is estimated that approximately 20% of the workers in industrialised nationsare shift workers (Eastman et al., 1995; United States Congress - Office of TechnologyAssessment, 1991). It is clear that some industries such as telecommunications, police, healthcare, military and transportation, must operate on a continuous twenty-four hour day, sevenday week schedule. To participate in the global marketplace, many companies are discoveringthat to stay competitive, they must consider adding some shift work to their company scheduleor move towards continuous operation. While strong economic incentives encouragebusinesses to adopt shift work, its use has drawbacks such as decreased production,increased accidents and increased health problems (Eastman et al., 1995; United StatesCongress - Office of Technology Assessment, 1991). With health issues alone, it has beenobserved that shift workers have higher risk of cardiovascular disease and gastro-intestinaldistress, as well as cognitive and emotional problems (Akerstedt, Knuttson, Alfredsson, &Theorell, 1984; Eastman et al., 1995; Moore-Ede, 1993; United States Congress - Office ofTechnology Assessment, 1991). Researchers believe that poor chronobiological adjustment toa permanent night shift or a rotating schedule may contribute to some of these ailments(Arendt, 1998a; Eastman et al., 1995; Moore-Ede, 1993; United States Congress - Office ofTechnology Assessment, 1991) .

As with treating jet lag, studies have indicated that properly timed exposure to brightlight exposure together with avoidance of bright light at the proper time can enhance theadaptation of the circadian system to changing shift schedules (Czeisler et al., 1990; Dawson& Campbell, 1991; Eastman, 1990a; Eastman, 1992; Eastman et al., 1995; Eastman & Martin,1999; Horowitz, Cade, Wolfe, & Czeisler, 2001; Lewy et al., 1987; Minors et al., 1991; Moore-Ede, 1993). Eastman and Martin (1999) have proposed a weekly schedule for permanentnight shift workers (11:00 – 07:00 shifts), using nightly three-hour exposures to approximately1200 lx white light starting at day 1 at 00:00 and advancing in start time one hour for five days.The worker should wear dark glasses and minimise time outdoors on the way home, thensleep from 08:00 to 15:00. On days off, the schedule assumes that there will be no night-timelight exposure, and the worker should delay sleep as late as possible (ideally, to 04:00 through12:00). On this schedule, the worker should maintain an adequate phase shift to maintainalertness at work, and should also be able to achieve sufficient sleep, which is possible whensleep is within the window of +/- 6 hours around the temperature minimum. For workers onvarying shifts, the problem is more complex, in that the state of the circadian phase dependson the history of shift rotations so that the calculation of appropriate light and dark exposuresis more difficult, as it is in the case of jet-lag. The principles of timing of light and dark relativeto minimum body temperature hold, but because circadian phase shifting is slow it may beimpossible to keep sleep and wake in the proper relation to this minimum (Eastman & Martin,1999).

Not all of the problems associated with shift work are solely the consequence of amaladapted biological clock. Shift workers generally have a tendency to be chronically sleep-deprived and experience domestic stresses that are independent of circadian adaptation(Eastman et al., 1995; Folkard & Monk, 1985; Reeth, 1998). Hence, there is no single solutionto the problems associated with shift work. A permanent night shift schedule, for example,might result in better circadian phase-shifting but will not resolve the problems of domestic life

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with people who are on a day shift schedule (Reeth, 1998). The application of light treatmentfor shift work problems remains in an experimental stage (Society for Light Treatment andBiological Rhythms, 1991), although general guidance exists for shift workers: Use brighterlight during the night shift; avoid conflicting light, such as bright light on the drive home; and,strictly use a regular daytime dark period for sleeping (Eastman et al., 1995; Eastman &Martin, 1999; Horowitz et al., 2001; Moore-Ede, 1993). As we learn more about the responseof the circadian system to night-time light exposures of varying durations, intensities, andtimes, we can expect practical recommendations to become more precise. For example, theknowledge that the circadian pacemaker is more sensitive to light exposure early in thebiological night than was previously thought might change illuminance recommendations forcircadian phase shifting (Zeitzer, Dijk et al., 2000).

4.5 Luminous modulation

The effects discussed above relate primarily to the spectral properties and intensity of lightexposure, and of course to the timing of the exposure. Separately from these variables, acharacteristic of some electric lighting systems might also influence health and performance.This is its rate of luminous modulation, or flicker. Flicker is a characteristic of discharge lamps(e.g., fluorescent lamps, HID lamps) when run on conventional, magnetic core-coil ballasts. Ingeneral, such lamps oscillate at a rate of twice the AC supply rate (i.e., 100 Hz in Europe, withits 50 Hz supply; 120 Hz in North America, with its 60 Hz supply). Although not perceived asvariable light sources, the human nervous system appears to operate in phase with thismodulation, up to approximately 145 Hz (Berman, Greenhouse, Bailey, Clear, & Raasch,1991). Electronic ballasts operate at 40 kHz, effectively making them continuous sources tothe human nervous system.

Low-frequency flicker might constitute a stressor, at least for some people. Kuller andLaike (1998) found that for individuals showing a high critical flicker fusion (CFF, the rate atwhich a flickering light is perceived as continuous), fluorescent lamps run on conventionalballasts reduced EEG alpha activity in comparison to electronic ballasts, although flicker ratedid not affect beta activity, heart rate or cardiac arrhythmia.

Several investigators, using a variety of methods, have found that flicker rates affecttask performance. Wilkins (1986) found that low-frequency (100 Hz) flicker detrimentallyaffected saccadic eye movements in reading, in comparison to 40 kHz. Veitch and McColl(1995) found, similarly, that low-frequency flicker reduced visual performance. Veitch andNewsham (1998) observed that participants working under magnetic ballasts (120 Hz)performed more poorly on creative writing and psychomotor performance tasks than thoseworking under electronic ballasts (40 kHz). However, these effects might be moderated byindividual differences in sensitivity: Küller and Laike (1998) found flicker effects on proof-reading task performance only for a subset of their participants, people having high CFFvalues.

Luminous modulation also appears to influence physical comfort and possibly health.In a field study in which ballasts in fluorescent luminaires were changed out overnight, so thatflicker rates changed without the participants' knowledge, while all other lighting conditionswere constant, rates of headache and eyestrain were lower when high-frequency electronicballasts were used (Wilkins, Nimmo-Smith, Slater, & Bedocs, 1989). The effects of suchmodulation on neuroendocrine function, if any, remain unknown.

Taken overall, the experimental results regarding the effects of low-frequencyluminous modulation add to the arguments for the adoption of energy-efficient electronicballasts for fluorescent lighting systems.

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5. THERAPEUTIC EFFECTS OF LIGHT

5.1 Mood disorders

5.1.1 Seasonal mood disorders

Suicide rates in the winter months are predicted by the hours of sunshine in the previousmonth, but not in the warmer, summer months (Egashira & Abe, 1994); in addition,seasonality of suicide rates in developed countries dropped during the 20th century, whenelectric lighting became prevalent.

Since the early 1980s, the medical community has recognised the existence of mooddisorders that recur seasonally (Lewy, Wehr, Goodwin, Newsome, & Rosenthal, 1981;Rosenthal et al., 1984). The most common of these is Seasonal Affective Disorder (SAD), alsoknown as seasonal depression, winter depression, or major depression with a seasonalpattern (Lam & Levitt, 1999). Lewy et al. (1981) sparked interest with their dramatic report ofpatient who experienced depression annually during the fall and winter months who wasobserved to improve from daily treatment with bright light exposure (Kern & Lewy, 1990; Lewy,Kern, Rosenthal, & Wehr, 1982)

Individuals who suffer from SAD experience recurrent episodes, usually during the falland winter months, with typical depressive symptoms such as emotional depression, a desireto withdraw socially, and a drop in physical energy, and additional cluster of symptoms that arenot typical of nonseasonal depression. These are an increased need for sleep, increasedappetite, unacceptable weight gain, and cravings for carbohydrates and sweets (Lam & Levitt,1999). Estimates of the occurrence of the syndrome range from 0,8% and 9,7% in NorthAmerica, but a consensus has formed that the true incidence lies between 1 and 3 % of thepopulation, with women more likely to suffer from SAD than men (Lam & Levitt, 1999).Approximately 8-9 % of the population might experience a milder form of mood disturbance,called sub-syndromal SAD (Mersch, Middendorp, Bouhuys, Beersma, & van den Hoofdakker,1999b).

Some surveys have found that people at northerly latitudes report a higher incidenceof depressive symptoms, particularly during the winter months, in comparison to moreequatorial locations (Hill, 1992; Küller, Ballal, Laike, & Mikellides, 1999). However, others haveargued that improved research designs eliminate these apparent latitude effects (Lam &Levitt, 1999). Indeed, there is stronger evidence for cultural or social differences betweenNorth America and Europe than for latitudinal differences (Mersch, Middendorp, Bouhuys,Beersma, & van den Hoofdakker, 1999a).

Patients with depression, both seasonal and non-seasonal, often show reducedimmune system activity. In one study, Seasonal Affective Disorder patients were successfullytreated with light therapy and also displayed a return to normal levels of a blood protein linkedto white blood cell activity (Avissar et al., 1999). In the summer, these patients wereasymptomatic and showed the same levels of this protein as did healthy people. The authorssuggested that this pattern of immune system activity might be a biological marker for SAD.Consistent with this hypothesis is evidence that seasonally breeding animals have seasonalrhythms of immunological competence (Nelson, Demas, Klein, & Kriegsfeld, 1995; Nelson,Demas, & Klein, 1998; Vriend & Lauber, 1973).

Considerable controlled research has examined the specific lighting parameters andexposure techniques for light treatment of winter depression (Lam, 1998; Rosenthal & Blehar,1989; Rosenthal, Sack, Skwerer, Jacobsen, & Wehr, 1988; Tam, Lam, & Levitt, 1995; Termanet al., 1989). Consensus has emerged in favour of 10000 lx for 30-45 minutes in the earlymorning as the standard treatment (Lam & Levitt, 1999).

Among those diagnosed with SAD, an estimated 65% respond favourably to daily lighttreatment, and there is a general consensus that this therapy is effective (Lam & Levitt, 1999;Rosenthal, 1993; Society for Light Treatment and Biological Rhythms, 1991). There are fewside-effects, and few patients for whom it is contraindicated (Lam & Levitt, 1999) (e.g.,patients with existing ophthalmological disorders, or who are taking photosensitizingmedications including antidepressant prescription or herbal medications (Lam & Levitt, 1999;

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Roberts, 1996; Roberts, Reme, Dillon, & Terman, 1992; Schey et al., 2000)). Drug treatments,particularly the selective serotonin reuptake inhibitors, are also effective, and sometimes arethe treatment of choice, particularly if the patient cannot or will not comply with the lighttreatment regimen (Lam & Levitt, 1999). Recurrence of the symptoms occurs rapidly if thepatient stops daily light therapy sessions during the winter months.

As with neuroendocrine and circadian regulation by light in healthy humans, lighttherapy appears to require exposure of the patients’ eyes versus their skin (Koorengevel et al.,2001; Lam & Levitt, 1999; Wehr et al., 1987). Currently, a variety of portable and semi-portable light devices are available for SAD therapy (Avery et al., 1993; Brainard & Bernecker,1991; Rosenthal et al., 1993; Stewart et al., 1990; Terman et al., 1990). Head-mounted visorsystems, shining closer to the eye, are a promising treatment modality that would allow thepatient more mobility and reduced energy costs (Rosenthal et al., 1993). The dominant form isa light box containing several fluorescent lamps, placed on a table top in front of the seatedpatient. The patient may read, knit, or do other sedentary activities, while glancing up at thelight every few moments (Lam & Levitt, 1999). Fluorescent lamps are most often usedbecause they are energy-efficient and because they do not produce as much unwanted heatas incandescent lamps. The colour properties of the white light are not important to thetreatment effect (Lee, Chan, Paterson, Janzen, & Blashko, 1997). Ultraviolet radiation is notnecessary to the treatment effect (Lam, Buchanan, Clark, & Remick, 1991; Lam, Buchanan,Mador, Corral, & Remick, 1992), and should be avoided because of its other harmful effects(Lam & Levitt, 1999).

The action spectrum for light therapy is unknown as yet, although evidence for thefeasibility of determining an action spectrum for light treatment exists of SAD exists. Brainardet al. (1990) treated patients with an equal photon dose (2,3 x 1015 photons/cm2/sec) of white,blue or red appearing light for one week, a photon density equivalent to a dosage of white lightknown to be therapeutically effective (Rosenthal et al., 1988; Terman et al., 1989). The photondensity emitted from the white light source elicited a significantly stronger clinical response ascompared to the results obtained from an equal photon density from the blue and red light.That result implied that light sources for SAD light therapy could not be improved bysubstituting narrower bandwidths of blue or red light in place of broadband white light. Asecond study was then done to compare restricted bandwidths of green light to red light at2,3 x 1015 photons/cm2/sec for treating winter depression (Oren et al., 1991). One week oflight treatment with green light produced a statistically-significant improvement of 51% lowermean Hamilton Depression Rating Scores (HDRS) scores. A 30% reduction in HDRS scoresfor the red-light group was not statistically significant. Therefore, at this photon density, greenlight was significantly stronger than the red light for treating winter depression. Consideredtogether, the results of these two experiments suggest that broad spectrum white light andnarrower band green light are equivalent in their capacity to reduce symptoms of SAD andform the basis for determining an action spectrum for light therapy of winter depression. Thetraditional approach to defining a complete action spectrum, however, requires testing withnarrower bandwidth light stimuli and more tightly controlled light exposures than is feasible inoutpatient clinical trials.

The origins and mechanisms underlying SAD and related seasonal mood disordersremain unknown. Initially, it appeared to involved a disruption in melatonin metabolismbecause of the known melatonin-suppressing effects of bright light; however, this hypothesishas been rejected (Lam & Levitt, 1999; Lee, Blashko, Janzen, Paterson, & Chan, 1997;Partonen & Lönnqvist, 1998). Other hypotheses that have attracted considerable attentioninclude the photoperiod hypothesis (that decreased day length in winter triggers the abnormalresponse; light therapy is thought to simulate increased day length); the photon counthypothesis (that decreased day length in winter results in too low a light dose for sustainedmental health); and, the circadian phase-shifting hypothesis (that SAD sufferers have anabnormal circadian rhythm, which light therapy corrects) (Lewy et al., 1987). None of thesefully accounts for the antidepressant effects of light therapy nor for the physiological functionsobserved in SAD patients (Lam & Levitan, 2000; Lam & Levitt, 1999; Lee, Blashko et al.,1997). However, interest in the circadian phase-shifting hypothesis remains keen, particularlybecause of advances in genetics that allow for more precise understanding of how circadianrhythms are regulated (Bunney & Bunney, 2000). Much research attention is focused on the

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neurotransmitter serotonin as a source of seasonal mood problems (Lam et al., 2000; Lam &Levitt, 1999; Partonen & Lönnqvist, 1998; Stain-Malmgren, Kjellman, & Åberg-Wistedt, 1998),although catecholamines may also play a role (Neumeister, Praschak-Rieder, Willeit, Stastny,& Kasper, 1999; Neumeister et al., 1998). SAD might be a heterogeneous condition ratherthan a simple instance of one type of biological abnormality (Lam & Levitan, 2000).

5.1.2 Other mood disorders

The treatment of specific illnesses with light is a rapidly developing frontier, extending beyondSAD. Among the first targets have been disorders bearing similarities to SAD, either insymptoms, temporal pattern, or neurohormonal changes. Major depression, without seasonalpattern, was among the first disorders studied. Investigators have had some success intreating non-seasonal depression with light therapy (Kripke, 1998; Kripke, Mullaney, Savides,& Gillin, 1989).

Eating disorders, such as bulimia nervosa and anorexia nervosa, have also seensuccessful light therapy treatment (Lam & Goldner, 1998; Lam, Goldner, Solyom, & Remick,1994). Premenstrual dysphoria (depressed mood associated with the menstrual cycle) showssimilarities to seasonal affective disorder (being a temporal pattern of depressed mood,although not a circadian pattern), and has also been successfully treated with light therapy(Kripke, 1993; Lam et al., 1999; Parry et al., 1989; Parry et al., 1993). Given the incompleteunderstanding of the etiology of these disorders, it is unsurprising that the therapeuticmechanism underlying successful light therapy also remains unknown.

Other disorders associated with disrupted circadian rhythms, particularly related tomelatonin, might also be good candidates for light therapy, although this possibility remains atthe level of speculation. These include cluster headache (Costa, Leston, Cavallini, & Nappi,1998), schizophrenia, and obsessive-compulsive disorder (Wetterberg, 1999). Arendt (1998a)cautioned that there is as yet no clear evidence for a circadian clock malfunction in psychiatricdisorders.

5.2 Sleep disorders

Given the potential for the use of light exposure to shift circadian rhythms, light therapy forcertain sleep disorders is an obvious application. (Circadian rhythm disruptions related to jetlag and shift work were discussed above, as they are not disease states.) Recognisedcircadian rhythm sleep disorders include the following (Wagner, 1999):

• delayed sleep phase syndrome – in which the individual cannot sleep before 2-3 a.m., andhas difficulty waking before late morning

• advanced sleep phase syndrome – in which the individual falls asleep very early, andwakens before dawn; this condition is very rare

• non-24-hour-sleep-wake cycle – found in the blind, and rarely in sighted people, thiscorresponds to a circadian clock in its free-running state, so that it is difficult to maintain aregular schedule of sleeping at night

• irregular sleep-wake cycles – in which the individual sleeps in several episodes each day,with little predictability in timing from one day to the next

Delayed sleep phase syndrome can result in chronic sleep deprivation, depending onthe individual need for sleep and the need to rise early for scheduled activities. The disordercan be co-existent with other medical or psychiatric problems, which should also be addressedeither before or during treatment for it (Wagner, 1999). Delayed sleep phase syndrome can besuccessfully treated with bright morning light (e.g., Rosenthal et al., 1990), particularly incombination with behavioural schedules (Arendt, 1998a; Chesson et al., 1999; Terman et al.,1995; Wagner, 1999).

Advanced sleep phase syndrome is very rare. Evening administration of bright lightcan delay the circadian phase and increase the sleeping time (Lack & Wright, 1993), howeverthis evidence is limited by the infrequency of the disorder (Arendt, 1998a; Chesson et al.,1999). Because non-24-hour-sleep-wake cycle is rare in sighted people, there have been still

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fewer opportunities to study the use of light therapy for this disorder. Morning light treatmenthas been used successfully to treat irregular sleep-wake cycles in otherwise healthyindividuals, together with strict behavioural schedules (Chesson et al., 1999; Wagner, 1999).

Sleep disturbances tend to increase with aging, together with a lower amplitude ofcircadian melatonin rhythms (Arendt, 1998a; Chesson et al., 1999). Some authors argue thatage-related insomnia resembles advanced sleep-phase syndrome, and that it can becorrected with evening administration of bright light (Wagner, 1999). Others, however, havefound that the circadian malsynchronization of older people who report sleep disturbances isvariable, comprising both phase advances and delays (Youngstedt, Kripke, Elliott, & Klauber,2001). Although evening light treatment can benefit elderly people who experience early-wakening insomnia (Arendt, 1998a; Campbell, Dawson, & Anderson, 1993), it probably is nota generic solution for all age-related sleep disorders (Chesson et al., 1999).

5.3 Circadian rhythms and medical treatment

Circadian rhythms exist in many physiological systems, including gastrointestinal functionsand the immune system (Arendt, 1998a; Plytycz & Seljelid, 1997). Thus, the effect of thetiming of administration in relation to the circadian phase state of the individual can influencethe effect of medications and treatments (Arendt, 1998a). This practice is known aschronotherapy or chronopharmacology.

Depending on the mechanism of action, the optimal treatment times could be at night[e.g., cancer treatments (Levi, 2000; Lissoni et al., 1992)], or during the day [e.g.,administration of beta-blockers for hypertension (Arendt, 1998a)]. Similarly, it appears that thetiming of treatments in relation to infradian rhythms such as the menstrual cycle can influencetreatment outcomes (Arendt, 1998a). Although the role of light therapy in chronotherapy isunknown, one possibility would be its use to synchronise circadian rhythms to ensure thattreatments are administered in their appropriate phase.

Arendt (1998a) has observed that the little that is known as yet represents "the tip ofthe iceberg" (p. 35). She pointed out that past research into drug efficacy and safety intendedto protect day-active humans has largely used the nocturnally active rat, with the result thatthe drugs were usually given during the rat’s night, but intended for use during our day. Thispractice has unknown implications for the efficacy and safety of current medical practice.

5.4 Neurological disorders: Alzheimer and related dementias

People with Alzheimer Disease and other dementias show circadian phase delays and sleepmore both at night and during the day, than healthy elderly people (Ancoli-Israel et al., 1997;Volicer, Harper, Manning, Goldstein, & Satlin, 2001). One reason for their disturbed circadianrhythms could be that severely demented people spend less time exposed to bright light,which could lead to disrupted patterns of melatonin release and suppression (Ancoli-Israel etal., 1997). Pathological examination has found SCN abnormalities in patients who had severedementia, making this another hypothesis for the circadian rhythm malfunctions (Stopa et al.,1999).

Someren, Kessler, Mirmiran and Swaab (1997) increased the general illuminationduring daytime hours in the living rooms of patients on a psychogeriatric ward in an ABAdesign (no treatment, light treatment, no treatment), and found that patients (who had avariety of diagnoses) exhibited less night-time restlessness during the week of light treatmentthan either before or after, improving the stability of the rest-activity rhythm. There have beenreports of success in using morning light to improve night-time sleep for agitated patients withdementia (Haffmans, Sival, Lucius, Cats, & van Gelder, 2001; Lyketsos, Lindell Veiel, Baker,& Steele, 1999), of patients with vascular dementia (Mishima, Hishikawa, & Okawa, 1998),and of Alzheimer Disease (Someren et al., 1999), and one clinical trial showing that eveninglight reduced night-time activity in Alzheimer patients with sundowning (increased confusionand agitation in early evening) (Satlin, Volicer, Ross, Herz, & Campbell, 1992).

There remains debate about the mechanism of the therapeutic effect, and about itsgeneralizability from one form of dementia to another (Mishima, Okawa, Hozumi, & Hishikawa,2000), but reviewers have concluded that it holds promise as a nonpharmacological treatment

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for behavioural and sleep-wake disturbances in this population, subject to further study withimproved research design controls (Chesson et al., 1999; Mishima et al., 2000; Opie,Rosewarne, & O’Connor, 1999). The research has not yet resulted in guidelines for lightintensities, treatment durations, or treatment timing.

6. RESEARCH METHODS IN LIGHTING

The studies reviewed here cover many disciplines, from biochemistry through physiology topsychology, and requiring knowledge of physics, statistics, and medicine. This technical reportcannot cover all of the research methods issues in all of these fields, for which in any casethere are textbooks. However, we have chosen to highlight a few important issues that are notalways adequately addressed by researchers in this field to draw attention to them by futureresearchers.

6.1 Measuring light

6.1.1 Stimulus specification

Complete specification of all aspects of the light stimulus is a requirement for research in thisarea. This includes a detailed description of the reflectances and surface characteristics of thesetting as well as the spectral properties of the source, its intensity, its position relative to theviewer, and the optical properties of the luminaire. Detailed information concerning the viewer(particularly the state of the visual and circadian systems at the time of testing) is alsorequired for complete stimulus specification (see below). The final report of CIE TechnicalCommittee 3-34, "Protocols for Describing Lighting" (currently in preparation) will provideguidance on this topic and should be consulted for details.

Stimulus specification is also important for architectural applications, especially ifintended to have therapeutic effects; otherwise designers will not know if the proposedinstallation will have the intended consequences. Designers also must make their clientsaware of the effects that changes in the setting (particularly of reflectances) could have on thelighting experienced by occupants. For example, even the best-designed system to deliverhigh illuminance will be ruined if the walls subsequently are painted a dark colour.

6.1.2 Photometric measurement

Most scientists and clinicians working on the circadian, neuroendocrine and therapeuticeffects of light in humans have predominantly used photopic illuminance as their standard lightmeasurement. Test subjects or patients were given light treatment at a specified illuminance(in lux or footcandles) for a specific length of time. Consequently, the elements of photopic luxand exposure time were the principal ingredients in formulating the intended dose of light.Similarly, the various light therapy devices are characterised as providing illuminances at agiven distance or upon a given surface.

Photopic photometry is based on the internationally accepted "standard observer"which has a normal three cone visual system adapted to daytime light levels (CIE, 1987). Thismeasurement system provides a serviceable nomenclature and technique for describing lighttherapy, but its use implies that the three cone, photopic visual system is responsible formediating the biological and therapeutic effects of light. If the normal, three cone, visualsystem is not the photoreceptor system through which light information is transduced for otherphysiological systems, as is suggested by the studies discussed above (Brainard et al., 2001a;Brainard et al., 2001b; Czeisler et al., 1995; Moore et al., 1995; Ruberg et al., 1996; Thapan etal., 2001), then the use of photopic photometric measures for nonvisual effects of lightbecomes questionable.

Figure 6 (p. 12.) shows how the spectral sensitivity curve for nonvisual respondingmight differ from both the photopic and scotopic sensitivity curves for vision. Although theexact curve is not yet known, it is possible that as information improves it will be possible todevelop a new weighting scheme for lighting measurement, a third sensitivity curve tocomplement V(λ), and V’(λ).

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Until that time, a complete specification of the light stimulus should be reported in allresearch reports. This would combine a detailed description of the spectral properties of thestimulus and the total irradiance, as received by the research subject. From this information,one can calculate if necessary the photopic (or scotopic) illuminance, or could use otherweighting functions that might be developed as the spectral sensitivities for nonvisualprocesses become better-understood.

Photometric measurement errors also require greater attention than has beencommon. Most common broad-band photometers (illuminance or luminance meters) arecalibrated to an incandescent standard, but when the light source is not incandescent (e.g.,fluorescent or compact fluorescent) the error rate can be much higher than one would expectfrom manufacturer’s specifications, because of the difference between the calibrationspectrum and the target spectrum (Ouellette, 1993). Ouellette found relative photometricerrors between 1 and 11% for measurements of triphosphor fluorescent lamps using variousmid-priced broad band photometers - errors which, in a therapeutic context or a physiologicalexperiment, could obscure dose-response relationships. The easiest solutions to this problemare to calibrate the photometer to a standard illuminant of the same type as the target, or touse a spectroradiometric photometer.

6.2 Light exposure and light dose

Both for experimental research and therapeutic efficacy, one must specify the quantity of lightreaching the observer - that is, corneal irradiance (or better, retinal irradiance), is the lightmeasurement that is most meaningful. This is a challenging task because the eye is dynamic;both the head and the eye are in constant motion relative to light sources. Eye blink, headmotion, eye motion, and eye closure can all influence the amount of light that is received. Inexperiments (or treatments) in which the individual is permitted to move freely within a space,accurate specification of the light dose is nearly impossible. This fact probably accounts forthe difficulty in observing consistent dose-response relationships between illuminance andmelatonin secretion at room illuminances (Brainard et al., 1997). Dawson and Campbell (1990)found that up to 80% of putative corneal illuminance can be lost if participants are free to altertheir gaze and distance from the light source.

Moreover, in many studies the investigator reports the horizontal illuminance at theworking plane (e.g., on the desk where the subjects work, as in Dollins et al. 1993), withoutspecifying the characteristics of the surfaces that surround the subject. The amount of lightthat reaches the eye of the subject depends on the reflectances of the illuminated surfaces; ifthe surfaces are dark, then the illuminance on the surface bears little relation to the lightreceived at the eye. Moreover, if the distribution of light is uneven, and the subject looks intoshadowy areas, the quantity of light received is further reduced.

The state of the eye further influences the light dose. The adaptation luminancedetermines the pupillary diameter: the wider the pupil, the greater the quantity of light reachingthe retina. Pupillary dilation influences the non-visual action of a given light stimulus (Gaddy,Rollag, & Brainard, 1993). Thus, if pupils are left to dilate or constrict in response to theexperimental or therapeutic stimulus, the final effect will be modified accordingly. For example,an intense light stimulus will cause pupil constriction, which will reduce the efficacy of thestimulus.

Both the quantity and the spectral qualities of the light reaching the retina depend onthe state of the lens and other ocular structures. In particular, the transmission properties ofthe lens change with age; a yellow pigmentation develops that restricts the ability of short-wavelength radiation to reach the retina (Brainard et al., 1997) (see Figure 7, p. 13.). This lossof light in the ultraviolet, violet, indigo and blue-green portions of the spectrum coincides withwhat is believed to be an important spectral region for some nonvisual light effects (Brainardet al., 2001a; Brainard et al., 2001b; Podolin et al., 1987; Takahashi et al., 1984; Thapan etal., 2001). Thus, the quantity and spectral properties of light reaching the cornea does notguarantee an accurate specification of the light stimulus for each subject.

Precision in research and treatment, therefore, ideally requires the followingspecifications:

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• the age and visual state of each subject;

• the adaptation (background) luminance when the stimulus is given;

• pupil diameter during the stimulus;

• where feasible, use of head restraints and gaze instructions;

• measurement at the eye, in the direction of gaze, of spectral irradiance (see section 5.1).

For architectural applications where nonvisual effects are to be triggered - forexample, in night shift work (see below) - practitioners should examine the design from theperspective of the location of occupants, and specifically should determine the illuminance thatwill be obtained at the most likely locations and direction of gaze of occupants’ eyes, to ensurethat the intended light dose is what will be delivered. This determination, of course, must takeinto account the visual system state of the most likely occupants and the spectralcharacteristics of the light source.

6.3 Research design issues

6.3.1 Placebo effects

When using light experimentally on humans for either therapeutic purposes or in work andtravel applications, the scientist runs the risk of finding a placebo reaction to the specific lighttreatments, in which participants’ behaviour fulfils either their own expectations for likelytreatment effects, or what they believe to be the experimenters’ expectancies. The classicreport cited as an example of this problem is the classic Hawthorne effect (Roethlisberger &Dickson, 1939; Snow, 1927). It is well known in the lighting community as the series ofexperiments in which regardless of the change in lighting level, workers’ performanceimproved. Some authors have suggested that this finding set back the development ofenvironmental psychology (the study of the physical environment on behaviour) by more than30 years (Gifford, 1997). Modern interpretations of the meaning of these experiments suggestthat poor research design, particularly the social context in which the experiments wereconducted, explains the contradictory results (Adair, 1984; Gifford, 1997; Jones, 1992).

Placebo issues are a concern for psychology, medicine and industrial research. Withinthe field of light therapy, this issue has been studied and discussed most insightfully byEastman (Eastman, 1990b; Eastman, Lahmeyer, Watell, Good, & Young , 1992) and by Byrneet al. (2000). One means to avoid placebo problems in lighting studies is to collect bothbehavioural and biological data. Subjective mood states and behavioural variables may bequite susceptible to the volunteers’ mental preconceptions, whereas objective biologicalvariables such as hormone levels, body temperature, and the like might be less likely to bedirectly influenced by a placebo response. Moreover, the use of multiple measures providesbetter insight into complex processes and protects against measurement errors (Cook &Campbell, 1979).

Another tactic is to carefully determine, at the conclusion of data collection, what werethe participant’s views about the experiment and about the influences on their responses(Adair, 1984), using this information to determine whether or not individuals with beliefs aboutwhat was expected of them show unduly biased results.

6.3.2 Eliminating alternative explanations

Biological and psychological research methods aim to provide causal inferences, and do so byeliminating competing explanations for the observed phenomena (Cook & Campbell, 1979).This is called internal validity. A complete exposition of research methods is beyond the scopeof this technical report, but many excellent textbooks review the area (Cook & Campbell, 1979;Kerlinger & Lee, 2000). Field studies of all kinds in particular require close attention andthought because strict control is usually impossible. For example, researchers concerned withthe effects of lighting in classrooms rarely are permitted to randomly assign participants toclasses with varying lighting conditions. This means that it is difficult to rule out differences inteacher behaviour, pre-existing differences between students, contagion within classes, or

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group social effects as alternative explanations for differences between classes at the end ofthe investigation.

6.3.3 Size and composition of research samples

External validity concerns the applicability of research findings to populations, settings, andtimes other than the one that was studied. Biological research addresses this question in partby studying a range of species, both animal and human, and examining the pattern of resultsfor similarities and differences (Argamaso et al., 1995). However, other external validityproblems remain. One of these is the heavy reliance on samples made up of only one sex(male or female), and interpreting results as applicable to both (Bird & Rieker, 1999; Dunnell,Fitzpatrick, & Bunting, 1999). This is a common practice, particularly for studying processes,such as neurohormonal processes, that could interact with reproductive cycles in women;however, the practice limits our knowledge (Legato, 1997). The only way to be certain that theprocesses work similarly in women to men is to systematically study women, as has beenrecommended by policy-making bodies (Baird, 1999).

Small samples sizes also pose an external validity threat because they risk notadequately representing the population to which one wishes to make inferences. Humans arehighly variable in their response to stimuli, so the results obtained by one small subset mightnot be typical of another. For example, the findings of a study of lighting effects on mood, ifthere were only 4 participants, would probably not capture the range of human emotionalresponses, particularly taking into consideration the mood states and personality traits that theparticipants would carry into the experiment. Similarly, given the variability of melatonin rhythmamplitude between subjects, studying a cohort of only four individuals could lead to misleadingconclusions.

Small samples also place statistical conclusions at risk by reducing the statisticalpower of the experiment (Cohen, 1988). Statistical power is the probability that an effect willbe found that is in fact present. Small effects are most vulnerable to low statistical power,whereas large effects can be detected even with small sample sizes. Reports of projects thathave failed to find statistically significant effects should be carefully scrutinised both for theadequacy of the sample size and for the possibility that the research design failed to controlfor all the possible variables that might have confounded or obscured the findings.

7. ARCHITECTURAL AND LIFE-STYLE APPLICATIONS

7.1 General principles

7.1.1 Principles for healthy lighting

Some general principles are beginning to emerge:

• The daily light dose received by people in Western countries might be too low.

Overall, the evidence suggests that current practice in Western countries provides for a verylow daily light exposure (Espiritu et al., 1994; Koller et al., 1993), a dose low enough topossibly be detrimental to our well-being (e.g., Espiritu et al., 1994). Exposure to bright light,either in light boxes or architecturally, might improve mood and health in people with very lowdaily light exposure (Partonen et al., 1998; Partonen & Lönnqvist, 2000). Other risks thatmight be associated with our low daily light dose, such as increased breast cancer risk orreduced immune function (Roberts, 2000; Stevens & Rea, 2001; Wehr, 1998), have potentiallygrave consequences. There is, however, as yet no agreement about the optimal daily lightdose.

• Healthy light is inextricably linked to healthy darkness.

Maintaining circadian rhythms requires periods of darkness in addition to periods of light(Eastman & Martin, 1999; Wehr, 1998). Changes to our habits -- such as not overextendingday length -- would seem also to be required to take full advantage of the powerful effects oflight on physiology and psychology. This would have the added benefit of providing adequatetime each day for sleep, which some argue that we do not do (Bonnet & Arand, 1995). Sleep

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deprivation in itself disrupts neuroendocrine function (Spiegel, Leproult, & Van Cauter, 1999).It is also possible that very low light levels overnight, while sleeping, might disrupt melatoninrhythms, as has been demonstrated in rats (Dauchy et al., 1999; Dauchy et al., 1997).Recommendations for the daily dark dose are perhaps as important as those for a daily lightdose, but do not yet exist.

• Light for biological action should be rich in the regions of the spectrum to which thenonvisual system is most sensitive.

Although the exact action spectrum is under debate, there is good evidence that it peaks inthe blue-green region of the spectrum (Brainard et al., 2001a; Thapan et al., 2001). The dailyrequirement for exposure to light of this wavelength range is not yet known, but this knowledgemight allow the design of light sources for optimal health effects without unnecessaryincreases in intensity. Such a solution could be more energy-efficient than a broad-bandsource that does not influence the nonvisual system as efficiently. Light sources for generalapplication, however, must maintain a balance between the needs of the visual and nonvisualsystems in all of their dimensions, to satisfy all of the purposes of the lighting system.

• The important consideration in determining light dose is the light received at the eye, bothdirectly from the light source and reflected off surrounding surfaces.

There is ample evidence that the nonvisual neuroendocrine effects of light are mediated byretinal photoreceptors (Eastman et al., 2000; Hebert et al., 1999; Koorengevel et al., 2001;Lockley et al., 1998). Lighting systems for biological action need to be assessed for the lightthey deliver to the eye, rather than the light emitted from or falling on any other surface.

• The timing of light exposure influences the effects of the dose.

It is clear that the sensitivity of the circadian system to light exposure varies significantly overthe 24-hour day (Gillette & Tischkau, 1999). Furthermore, the effects of light exposure dependon prior exposures (Wehr, 1991; Wehr et al., 1995). Thus, recommendations for practicalapplications need to be specific to the time of day and might need to take into account thepattern of exposures over time.

7.1.2 Fundamentals of lighting quality

Good-quality lighting includes lighting for health (Veitch et al., 1998), in parallel with meetingthe other needs of people who will occupy the lit space (Figure 1). Principles of good lightingpractice should be the starting point for lighting design; we can expect that these might beamended as our knowledge about what constitutes healthy light improves. These principlesinclude energy-efficiency and environmental considerations that should not be forgotten.Healthy light in the broadest sense must also be ecologically sound.

Recommended practice and standards documents articulate current consensus aboutgood-quality lighting (e.g., Chartered Institution of Building Services Engineers (CIBSE), 1994;(CIE, 1986). Perhaps the most advanced statement to date about lighting quality is the 9thedition of the IESNA Lighting Handbook, with its Lighting Design Guide that identifies therelative importance of various luminous conditions for various settings and tasks (IlluminatingEngineering Society of North America (IESNA), 2000). Some of the principles that havespecial relevance for providing biologically active lighting are the following:

• The colours and reflectances of room surfaces are part of the lighting system. Darksurfaces will negate the benefits of providing additional luminaires, and are likely to resultin an unsatisfactory luminous environment in which there is little indirect or reflected light.

• Bright vertical room surfaces are generally preferred over dark ones, provided that glare iscontrolled (Collins et al., 1999; Veitch & Newsham, 1998; Veitch & Newsham, 2000).

• Controlled use of daylighting, limiting glare and solar heat gain to avoid compromisingcomfort, is an energy-efficient strategy for providing more light where it is wanted and,perhaps, needed - although, of course, it is not a light source available for night shiftlighting.

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7.2 Lighting for daytime activity

Detailed instructions for daytime lighting based on current knowledge are problematic.Increasing illuminance levels does not appear to have lasting effects on cognitive workperformance (Gifford et al., 1997; Veitch, 2001). This suggests that for employers there is noimmediate benefit to increased light levels for the day shift. There might be beneficial effectson mental health associated with increasing the daily light dose, and perhaps additional healthbenefits, as discussed above. At present, however, we do now know what the optimal dailylight exposure might be, nor when (in relation to the circadian rhythm) it should be timed.Partonen et al. (1998) obtained striking results with increased light exposure amounting tothree hours a week, in a specific setting, the gymnasium, in winter at a high latitude (inFinland). In another study, people with SAD were successfully treated with a 1-hr walk outsideeach morning. The daylight group were exposed to approximately 1000 lx (early morningwinter in Europe, often overcast), whereas the comparison group were less successfullytreated with 2800 lx of electric light for half an hour each morning (Wirz-Justice et al., 1996).

This pattern of findings suggests the following, very tentative, suggestions for ways toachieve healthy light exposure by modifying good existing lighting practices:

• Provide opportunities for increased light exposure by good use of daylight, making full useof architectural opportunities to provide energy-efficient, high-intensity light with a spectralbalance for the visual and nonvisual systems (see Figure 8.).

Figure 8. This daylit office features split exterior blinds, which allow the occupant to preventdirect glare through the lower section (shown closed) while lighting the office with daylightthrough the upper section (shown partly closed). Photo © Fraunhofer ISE, 2001.

• Provide biologically-active light where the eye is, not throughout the space, while avoidingthe creation of uncomfortable glare. Rather than providing increased illuminancethroughout interiors, increase light exposure by providing areas of higher illuminancewhere they will be frequently viewed. This use of non-uniform light distribution will help toavoid conflict between the need to be energy-efficient and the delivery of higherilluminances for at least some of the time. For example, high-intensity task lamps in areasof lower general illumination might achieve this goal.

• Use local control where feasible, and particularly where daylight is available. Higherilluminances all day are unlikely to be necessary to the biological effect given the lowersensitivity of the circadian system at certain points in the rhythm. Controls will allow light tobe delivered when needed, and energy to be saved when it is not. They also are likely tobe the only means to tailor lighting to individual needs and desires (Newsham & Veitch,2001).

Healthy light for people on day shifts is also a matter of healthy habits. It might be thecase that an adequate light dose could be obtained by a daytime walk outdoors; the exercise

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would provide an added health benefit. Light avoidance during some portion of the nightappears to be a necessary behavioural component of the system.

7.3 Lighting for night shifts

One setting where the potential application is clear is night shift work. Bright light exposureduring the night shift can have immediate, acute effects on complex task performance (e.g.,Badia et al., 1991; Boyce et al., 1997; Daurat et al., 1993; French et al., 1990) and can aid insuccessful circadian phase-shifting (Eastman & Martin, 1999). The optimal dose, duration,and timing are not yet known (Zeitzer, Dijk et al., 2000). The bright light might not be neededconstantly throughout the shift, but with additional luminaires and appropriate switching(elaborate automated controls are available but would not be necessary to the purpose),biologically effective lighting could be provided to those who must work overnight. Potentialbenefits of doing so include improved employee performance, improved health and decreasedaccidents during shift work, and these outweigh the costs of providing appropriate night-shiftlighting (Electric Power Research Institute (EPRI), 1986). Suggestions for how this might beachieved include the following:

• Design delivery schedules that are appropriate to the shift pattern (cf. Eastman & Martin,1999). Circadian phase-shifting might not be desirable (for instance, in a rapidly-rotatingshift schedule).

• Ensure that when bright light exposure is needed, it is delivered to the worker’s eye (asabove, it need not be uniform in the space in order to achieve this goal) (see Figure 9).

Figure 9. One way to deliver bright light to where it will be seen is to use a task-ambientcombination, with areas of high illuminance provided locally by task lighting. Photo © 1996,National Research Council Canada.

As noted above, this would not be the entire solution to the problems of adapting toshift work, but the contribution would be significant. Behavioural routines faithfully practised bythe worker are a necessary component of maintaining a healthy pattern of light-dark cycleswhen working the night shift.

8. CONCLUSION

Exploring the behaviour of light and the mechanisms of vision has been a passion forphilosophers and scientists for two millennia or more (Zajonc, 1995). As a result we have well-developed recommendations for lighting practice based largely on visual system requirements(CIE, 2001b; Illuminating Engineering Society of North America (IESNA), 2000; Stevens &Rea, 2001).

In contrast, the empirical study of the nonvisual, systemic effects of light is relativelynew, spanning only a few decades. These decades have seen rapid advances in which

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controlled laboratory and clinical studies have demonstrated that light can influence humanphysiology, mood and behaviour. We are developing light treatments for specific clinicaldisorders as well as improving adaptation to shift work and jet travel. These advances,however, are not yet enough to support clear statements about the optimal light and darkneeds for good human health, nor to lead to modifications or adaptations of lighting practicethat blend the requirements for good health with the requirements for the visually-mediatedprocesses implicated in human response to the lit environment (cf., Stevens & Rea, 2001).Researchers from many disciplines and lighting practitioners of all kinds will need tocollaborate to attain that goal. The challenges involved are many (Veitch et al., 1998), but thatthe effort is worthwhile we do not doubt.

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TOSINI, G. (2000). Melatonin circadian rhythm in the retina of mammals. ChronobiologyInternational, 17(5), 599-612.

TUUNAINEN, A., KRIPKE, D. F., CRESS, A. C., & YOUNGSTEDT, S. D. (2001). Retinalcircadian rhythms in humans. Chronobiology International, 18(6), 957-971.

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VEITCH, J. A. (1998). Commentary: On unanswered questions. In J. A. Veitch (Ed.),Proceedings of the First CIE Symposium on Lighting Quality. CIE x015-1998, pp. 88-91.

VEITCH, J. A. (2001). Lighting quality contributions from biopsychological processes. Journalof the Illuminating Engineering Society, 30(1), 3-16.

VEITCH, J. A., & GIFFORD, R. (1996). Assessing beliefs about lighting effects on health,performance, mood and social behavior. Environment and Behavior, 28, 446-470.

VEITCH, J. A., HINE, D. W., & GIFFORD, R. (1993). End-users’ knowledge, beliefs, andpreferences for lighting. Journal of Interior Design, 19(2), 15-26.

VEITCH, J. A., JULIAN, W., & SLATER, A. I. (1998). A framework for understanding andpromoting lighting quality. In J. A. Veitch (Ed.), Proceedings of the First CIE Symposium onLighting Quality. CIE x015-1998, pp. 237-241.

VEITCH, J. A., & MCCOLL, S. L. (1995). Modulation of fluorescent light: Flicker rate and lightsource effects on visual performance and visual comfort. Lighting Research and Technology,27(4), 243-256.

VEITCH, J. A., & NEWSHAM, G. R. (1998). Lighting quality and energy-efficiency effects ontask performance, mood, health, satisfaction and comfort. Journal of the IlluminatingEngineering Society, 27(1), 107-129.

VEITCH, J. A., & NEWSHAM, G. R. (2000). Preferred luminous conditions in open-planoffices: Research and practice recommendations. Lighting Research and Technology, 32,199-212.

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VOLICER, L., HARPER, D. G., MANNING, B. C., GOLDSTEIN, R., & SATLIN, A. (2001).Sundowning and circadian rhythms in Alzheimer’s disease. American Journal of Psychiatry,158(5), 704-711.

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VON SCHANTZ, M., PROVENCIO, I., & FOSTER, R. G. (2000). Recent developments incircadian photoreception: More than meets the eye. Investigative Ophthalmology & VisualScience, 41(7), 1605-1607.

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PUBLICATIONS

Recommendations

17.4 International lighting vocabulary, 4th ed. (Jointpublication IEC/CIE), 1987.

23 International recommendations for motorwaylighting, 1973.

39.2 Recommendations for surface colours forvisual signalling, 2nd ed., 1983.

Standards

ISO 10526/CIE S005 CIE standard illuminants forcolorimetry, 1999.

ISO/CIE 10527 Colorimetric observers, 1991 (S002,1986).

CIE S 004-1998 Colours of light signals (Draftstandard), 1998.

ISO 16508/CIE S006 Road traffic light — 200 mmroundel signals photometric properties, 1998.

ISO 17166/CIE S007 Erythema reference actionspectrum and standard erythema dose, 1998.

ISO 8995/CIE S 008-2001 Lighting of indoor workplaces.

CIE S 009:2002 Photobiological safety of lamps andlamp systems.

CIE S 011:2003 Spatial Distribution of Light.CIE DS 010.2-2001 Photometry – The CIE system of

physical photometry.CIE DS 012.2:2002 Standard method of assessing

the spectral quality of daylight simulators forvisual appraisal and measurement of colour.

CIE DS 013.2:2002 International Standard Global UVIndex.

CIE DS 015.1:2002 Lighting of work places – outdoorwork places

Technical Committee Reports

1 Guide lines for minimising urban sky glow nearastronomical observatories (Joint publicationIAU/CIE), 1980.

13.3 Method of measuring and specifying colourrendering of light sources, 1995.

15.2 Colorimetry, 2nd ed., 1986.16 Daylight, 1972.18.2 The basis of physical photometry, 2nd

ed., 1983.19.21 An analytic model for describing the influence

of lighting parameters upon visualperformance, 2nd ed., Vol.1.: Technicalfoundations, 1981.

19.22 An analytic model for describing the influenceof lighting parameters upon visualperformance, 2nd ed., Vol.2.: Summary andapplication guidelines, 1981.

23 International recommendations formotorlighting, 1973.

31 Glare and uniformity in road lightinginstallations, 1976.

32 Lighting in situations requiring specialtreatment (in road lighting), 1977.

33 Depreciation of installation and theirmaintenance (in road lighting), 1977.

34 Road lighting lantern and installation data:photometrics, classification andperformance, 1977.

38 Radiometric and photometric characteristics ofmaterials and their measurement, 1977.

40 Calculations for interior lighting: Basicmethod, 1978.

41 Light as a true visual quantity: Principles ofmeasurement, 1978.

42 Lighting for tennis, 1978.43 Photometry of floodlights, 1979.44 Absolute methods for reflection

measurements, 1979.45 Lighting for ice sports, 1979.46 A review of publications on properties and

reflection values of material reflectionstandards, 1979.

47 Road lighting for wet conditions, 1979.48 Light signals for road traffic control, 1980.

49 Guide on the emergency lighting of buildinginteriors, 1981.

51.2 A method for assessing the quality of daylightsimulators for colorimetry, 1999.

52 Calculations for interior lighting: Appliedmethod, 1982.

53 Methods of characterising the performance ofradiometers and photometers, 1982.

54.2 Retroreflection: Definition andmeasurement, 2001.

55 Discomfort glare in the interior workingenvironment, 1983.

57 Lighting for football, 1983.58 Lighting for sports halls, 1983.59 Polarisation: Definitions and nomenclature,

instrument polarisation, 1984.60 Vision and the visual display unit work

station, 1984.61 Tunnel entrance lighting: A survey of

fundamentals for determining the luminance inthe threshold zone, 1984.

62 Lighting for swimming pools, 1984.63 The spectroradiometric measurement of light

sources, 1984.64 Determination of the spectral responsivity of

optical radiation detectors, 1984.65 Electrically calibrated thermal detectors of

optical radiation (absolute radiometers), 1985.66 Road surfaces and lighting (joint technical

report CIE/PIARC), 1984.67 Guide for the photometric specification and

measurement of sports lightinginstallations, 1986.

69 Methods of characterising illuminance metersand luminance meters: Performance,characteristics and specifications, 1987.

70 The measurement of absolute luminousintensity distributions, 1987.

72 Guide to the properties and uses ofretroreflectors at night, 1987.

73 Visual aspects of road markings (joint technicalreport CIE/PIARC; French translation: Aspectsvisuels des marquages routiers is availablefrom PIARC), 1988.

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74 Roadsigns, 1988.75 Spectral luminous efficiency functions based

upon brightness matching for monochromaticpoint sources, 2° and 10° fields, 1988.

76 Intercomparison on measurement of (total)spectral radiance factor of luminescentspecimens, 1988.

77 Electric light sources: State of the art -1987, 1988.

78 Brightness-luminance relations: Classifiedbibliography, 1988.

79 A guide for the design of road trafficlights, 1988.

80 Special metamerism index: Change inobserver, 1989.

81 Mesopic photometry: History, special problemsand practical solutions, 1989.

82 CIE History 1913 - 1988, 1990.83 Guide for the lighting of sports events for

colour television and film systems, 1989.84 Measurement of luminous flux, 1989.85 Solar spectral irradiance, 1989.86 CIE 1988 2° spectral luminous efficiency

function for photopic vision, 1990.87 Colorimetry of self-luminous displays - A

bibliography, 1990.88 Guide for the lighting of road tunnels and

underpasses, 1990.89 Technical Collection 1990:

89/1 Results of a CIE detector responseintercomparison

89/2 Photobiological effects of sunlamps89/3 On the deterioration of exhibited

museum objects by optical radiation89/4 Guide for the measurement of

underground mine lighting.90 Sunscreen testing (UV.B), 1991.93 Road lighting as an accident countermeasure,

1992.94 Guide for floodlighting, 1993.95 Contrast and visibility, 1992.96 Electric light sources - State of the art, 1992.97 Maintenance of indoor electric lighting

systems, 1992.98 Personal dosimetry of UV radiation, 1992.99 Lighting education (1983-1989), 1992.100 Fundamentals of the visual task of night

driving, 1992.101 Parametric effects in colour-difference

evaluation, 1993.102 Recommended file format for electronic

transfer of luminaire photometric data, 1993.103 Technical Collection 1993:

103/1 Colour appearance analysis103/2 Industrial lighting and safety at work103/3 Reference action spectra for ultraviolet

induced erythema and pigmentation ofdifferent human skin types

103/4 Biologically effective emissions andhazard potential of desk-top luminairesincorporating tungsten halogen lamps

103/5 The economics of interior lightingmaintenance

103/6 Clarification of maintained illuminanceand associated terms.

104 Daytime running lights (DRL), 1993.105 Spectroradiometry of pulsed optical radiation

sources, 1993.106 CIE Collection in Photobiology and

Photochemistry, 1993:106/1 Determining ultraviolet action spectra106/2 Photokeratitis106/3 Photoconjunctivitis106/4 A reference action spectrum for

ultraviolet induced erythema in humanskin

106/5 Photobiological effects in plant growth

106/6 Malignant melanoma and fluorescentlighting

106/7 On the quantification of environmentalexposures: limitations of the concept ofrisk-to-benefit ratio

106/8 Terminology for photosyntheticallyactive radiation for plants.

107 Review of the official recommendations of theCIE for the colours of signal lights, 1994.

108 Guide to recommended practice of daylightmeasurement, 1994.

109 A method of predicting corresponding coloursunder different chromatic and illuminanceadaptation, 1994.

110 Spatial distribution of daylight - Luminancedistributions of various reference skies, 1994.

111 Variable message signs, 1994.112 Glare evaluation system for use within outdoor

sports- and area lighting, 1994.113 Maintained night-time visibility of retroreflective

road signs, 1995.114 CIE Collection in photometry and radiometry,

1994:114/1 Survey of reference materials for

testing the performance ofspectrophotometers and colorimeters

114/2 International intercomparison ontransmittance measurement - Report ofresults and conclusions

114/3 Intercomparison of luminous fluxmeasurements on HPMV lamps

114/4 Distribution temperature and ratiotemperature

114/5 Terminology relating to non-selectivedetectors

114/6 Photometry of thermally sensitivelamps.

115 Recommendations for the lighting of roads formotor and pedestrian traffic, 1995.

116 Industrial colour-difference evaluation, 1995.117 Discomfort glare in interior lighting, 1995.118 CIE Collection in colour and vision, 1995:

118/1 Evaluation of the attribute ofappearance called gloss

118/2 Models of heterochromatic brightnessmatching

118/3 Brightness-luminance relations118/4 CIE guidelines for co-ordinated

research on evaluation of colourappearance models for reflection printand self-luminous display imagecomparisons

118/5 Testing colour appearance models:Guidelines for co-ordinated research

118/6 Report on color difference literature118/7 CIE guidelines for co-ordinated future

work on industrial colour-differenceevaluation.

121 Photometry and goniophotometry of luminaires,1996.

122 The relationship between digital andcolorimetric data for computer-controlled CRTdisplays, 1996.

123 Low Vision - Lighting needs for the partiallysighted, 1997.

124 CIE Collection in Colour and Vision, 1997:124/1 CIE TC 1-31 Report: Colour notations

and colour order systems124/2 CIE TC 1-18 Chairman's Report: On

the course of the disability glarefunction and its attribution tocomponents of ocular scatter

124/3 Next step in industrial colour differenceevaluation, Report on a colourdifference research meeting.

125 Standard erythemal dose — A review, 1997.126 Guidelines for minimizing sky glow, 1997.

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127 Measurement of LEDs, 1997.128 Guide to the lighting for open-cast mines,

1998.129 Guide for lighting exterior work areas, 1998.130 Practical methods for the measurement of

reflectance and transmittance, 1998.131 The CIE 1997 interim colour appearance model

(simple version), CIECAM97s, 1998.132 Design methods for lighting of roads, 1999.134 CIE Collection in Photobiology and

Photochemistry, 1999.134/1 CIE TC 6-26 Report: Standardization of

the terms UV-A1, UV-A2 and UV-B134/2 CIE TC 6-30 Report: UV protection of

the eye134/3 CIE TC 6-38 Report: Recommendation

on photobiological safety of lamps. Areview of standards

135 CIE Collection 1999: Vision and colour,physical measurement of light and radiation.135/1 Disability Glare135/2 Colour rendering, closing remarks135/3 Virtual metamers for assessing the

quality of simulators of CIE illuminantD50 (Supplement 1-1999 to CIE 51-1981)

135/4 Some recent developments in colour-difference evaluation

135/5 Visual adaptation to complexluminance distribution

135/6 45°/0° Spectral reflectance factors ofpressed polytetrafluoroethylene (PTFE)power (Reprint of NIST Technical Note1413)

136 Guide to the lighting of urban areas, 2000.137 The conspicuity of traffic signs in complex

background, 2000.

138 CIE Collection 2000: Photobiology andPhotochemistry.

138/1 Blue-light photochemical retinal hazard138/2 Action spectrum for photocarcino-genesis

(non-melanoma skin cancers)138/3 Standardized protocols for

photocarcinogenesis safety testing138/4 A proposed global UV index.139 The influence of daylight and artificial light on

diurnal and seasonal variations in humans. Abibliography, 2001.

140 Road lighting calculations, 2000.141 Testing of supplementary systems of

photometry, 2001.142 Improvement to industrial colour-diffence

evaluation, 2001.143 International recommendations for colour

vision requirements for transport, 2001.144 Road surface and road marking reflection

characteristics, 2001.145 The correlation of models for vision and visual

performance, 2002.146/147 Collection on Glare, 2002.

146 CIE equations for disability glare147 Glare from small, large and complexsources.

148 Action spectroscopy of skin with tunablelasers, 2002.

149 The use of tungsten filament lamps assecondary standard sources, 2002.

150 Guide on the limitation of the effects ofobtrusive light from outdoor lightinginstallations, 2003.

151 Spatial weighting of solar ultraviolet radiation,2003.

Proceedings of the Sessions:

1921 Paris1924 Genèva1927 Bellagio1928 Saranac1931 Cambridge1935 Berlin1939 Scheweningen1948 Paris1951 Stockholm1955 Zürich1959 4-7 Bruxelles (Vol. A,B,C,D)

1963 11 Vienna (Vol. A,B,C,D)1967 14 Washington (Vol. A,B)1971 21 Barcelona (Vol. A,B,C)1975 36 London1979 50 Kyoto1983 56 Amsterdam1987 71 Venice, Vol.1-21991 91 Melbourne, Vol.1-21995 119-120 New Delhi, Vol. 1-21999 133 Warsaw, Vol. 1-2

Discs and other publications

D001 Disc version of CIE Colorimetric Data (S001and S002 Tables), 1988.

D002 Disc version of CIE Colorimetric and ColourRendering Data (Publ. 13.2 and 15.2 Tables),1991.

D003 CIE Roster.D005 A method for assessing the quality of D65

daylight simulators for colorimetry (based onCIE 51-1981) 1994.

D006 Automatic quality control of daylightmeasurement - Software for IDMP stations(computer program to CIE 108-1994), 1994.

D007 A computer program implementing the "Methodof predicting corresponding colours underdifferent chromatic and illuminance adaptation"(described in CIE 109-1994), 1994.

D008 Computer program to calculate CRIs(according to CIE 13.3-1995), 1995.

x005 Proceedings of the CIE Seminar '92 onComputer programs for light and lighting.

x006 Japan CIE Session at PRAKASH 91.x007 Proceedings of the CIE Symposium '93 on

Advanced Colorimetry.x008 Urban sky glow - a worry for astronomy

(Proceedings of a Symposium of CIE TC 4-21),1994.

x009 Proceedings of the CIE Symposium '94 onAdvances in Photometry.

x010 Proceedings of the CIE Expert Symposium '96Colour Standards for Image Technology.

x011 Special volume, 23rd Session, New Dehli ’95,Late papers.

x012 NPL — CIE-UK Visual Scales Conference.x013 Proceedings of the CIE LED Symposium ’97 on

Standard Methods for Specifying andMeasuring LED Characteristics, 1998.

x014 Proceedings of the CIE Expert Symposium ’97on Colour Standards for Imaging Technology,1998.

x015 Proceedings of the First CIE Symposium onLighting Quality, 1998.

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x016 Proceedings of the CIE/ICNIRP Conference onMeasurements of Optical Radiation Hazards,1998.

x017 Special volume, 24th Session, Warsaw ’99,Late papers, 2000.

x018 Proceedings of the CIE Symposium ’99 “75Years of CIE Photometry”, 2000.

x019 Proceedings of three CIE workshops onCriteria for Road Lighting, 2001.

x020 Proceedings of the CIE Symposium 2001“Uncertainty Evaluation, Methods for Analysisof Uncertainties in Optical RadiationMeasurement”, 2001.

x021 Proceedings of the CIE Expert Symposium2000 "Extended range colour spaces", 2001.

x022 Proceedings of the 2nd CIE Expert Symposiumon LED measurement ”Standard methods forspecifying and measuring LED and LED clustercharacteristics, 2001.

x023 Proceedings of two CIE Workshops onphotometric measurement systems for roadlighting installations, 2002.

x024 Proceedings of the CIE/ARUP Symposium onVisual Environment, 2002.

x025 Proceedings of the CIE Symposium 2002 on"Temporal and Spatial Aspects of Light andColour Perception and Measurement, 2003.

CIE publications on CD-ROM

A CD-ROM with all current CIE Technical Reports and Standards is available from IHS,

Information Handling Services, 15 Inverness Way East, M/S B203 Englewood, Colorado 80112-5776 USA.

CIE-Journal Vol.1 - Vol.8 1982 - 1989. CIE NEWS No. 1 - No. 66 1986 - 2003.

For latest information on CIE publications see the CIE Home Page on the World Wide Web:

http://www.cie.co.at/cie/