Review: The Impact of Light in Buildings on Human Health

Abstract

The effects of light on health can be divided into three sections. The first is that of light as radiation. Exposure to the ultraviolet, visible, and infrared radiation produced by light sources can damage both the eye and skin, through both thermal and photochemical mechanisms. Such damage is rare for indoor lighting installations designed for vision but can occur in some situations. The second is light operating through the visual system. Lighting enables us to see but lighting conditions that cause visual discomfort are likely to lead to eyestrain. Anyone who frequently experiences eyestrain is not enjoying the best of health. The lighting conditions that cause visual discomfort in buildings are well known and easily avoided. The third is light operating through the circadian system. This is known to influence sleep patterns and believed to be linked to the development of breast cancer among night shift workers.
There is still much to learn about the impact of light on human health but what is known is enough to ensure that the topic requires the attention of all those concerned with the lighting of buildings.

Full text

The impact of light in buildings on human health
Peter R Boyce1
1 Professor Emeritus, Rensselaer Polytechnic Institute
60, Riverside Close, Bridge, Canterbury, Kent CT4 5TN, Great Britain
E-mail: peter@boycepeter.freeserve.co.uk
Tel: 01227-833867
Abstract
The effects of light on health can be divided into three classes. The first is that of light as
radiation. Exposure to the ultra-violet, visible and infrared radiation produced by light
sources can damage both the eye and skin, through both thermal and photochemical
mechanisms. Such damage is rare for indoor lighting installations designed for vision but
can occur in some situations. The second is light operating through the visual system.
Lighting enables us to see but lighting conditions that cause visual discomfort are likely to
lead to eyestrain. Anyone who frequently experiences eyestrain is not enjoying the best of
health. The lighting conditions that cause visual discomfort in buildings are well known and
easily avoided. The third is light operating through the circadian system. Light operating
through the circadian system is known to influence sleep patterns and believed to be linked
to the development of breast cancer among night shift workers. There is still much to learn
about the impact of light on human health but what is known is enough to ensure that the
topic requires the attention of all those concerned with the lighting of buildings.
Keywords: Light; health; buildings; radiation; visual system; circadian system
Short title: Light exposure and human health
1. Introduction
This paper is concerned with the impact of light in buildings on human health. From the start
it is necessary to explain what is meant by the terms light, buildings and health. Light is
conventionally defined as electromagnetic radiation in the wavelength range 380 to 780 nm.
However, most light sources used in buildings produce both ultra-violet and infrared
radiation as well as visible radiation. In this situation, the simplest approach is to consider
light to include these wavelengths as well.
As for buildings, these can take many forms but the ones of interest here are those where
people are likely to be present for prolonged periods. Even these can vary widely in the
nature of the occupants and the type of lighting provided; from schools to hospitals, from
factories to homes, from offices to shops.
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Health is defined by the World Health Organization as “a state of complete physical, mental
and social well-being and not merely the absence of disease and infirmity”. Well-being is
defined by Webster’s dictionary as “a good or satisfactory condition of existence; a state
characterized by health, happiness and prosperity”. The problem with such definitions is that
they are so wide as to be virtually meaningless. On the basis of these definitions, there are
very few events or environments that would not influence health and well-being, lighting
being just one of many. Here, health will be more strictly defined as the absence of disease
or infirmity. Further, the effects on health considered are restricted to those where there is
scientific evidence for the importance of light exposure.
Having defined these terms it is now necessary to consider two other factors that influence
the impact of light on human health. These are the health status of the people exposed and
the types of lighting to which they are exposed. In this paper, attention will be given to
people who are healthy and to groups of people who have conditions that make them
sensitive to light exposure. As for the forms of lighting, those considered here are what
might be called the conventional, i.e., those designed to enable people to see and that follow
the recommendations made by authoritative bodies (1,2). This excludes some forms of
lighting designed to use light as a source of radiation for industrial or medical purposes or
for entertainment.
There are three routes whereby exposure to light can influence human health, as radiation on
the eye and skin, through the visual system and through the circadian system. Each will be
examined in turn.
2. Light as radiation
People typically spend many hours in buildings bathed in the ultra-violet, visible and infra-
red radiation produced by natural or electric lighting. This radiation can damage tissue
regardless of whether or not it affects the visual and circadian systems.
2.1 Tissue damage by ultraviolet radiation.
Exposure to ultraviolet radiation affects both eye and skin. For the eye, exposure to
ultraviolet radiation can produce photokeratitis of the cornea. This is a very unpleasant but
temporary condition that can result in severe pain beginning several hours after exposure and
persisting for twenty-four hours or longer (3). The symptoms of photokeratitis are clouding
of the cornea, reddening of the eye, tearing, photophobia, twitching of the eyelids and a
feeling of grit in the eye. Typically, all these symptoms clear up within about forty-eight
hours. Photokeratitis occurs because of a photochemical reaction to ultra-violet radiation at
the cornea, but not all the ultraviolet radiation incident on the eye is absorbed at the cornea,
some reaches the lens. The effect of exposing the lens to ultraviolet radiation can be to
produce a cataract, an opacity that absorbs and scatters light, thereby severely degrading the
retinal image. This can occur over two time-scales, acute, a few hours after exposure, and
chronic, after many years of exposure
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Exposure to ultraviolet radiation also has an effect on the skin. Within a few hours of
exposure, the skin reddens. This reddening is called erythema. Erythema reaches a maximum
about eight to twelve hours after exposure and fades away after a few days. High dose
exposures may results in oedema, pain, blistering and, after a few days, peeling of the skin,
i.e., sunburn. Repeated exposure to ultraviolet radiation produces a protective response in the
skin in that pigment migration to the surface of the skin occurs and a new darker pigment is
formed. Coincident with this, the outer layer of the skin thickens producing a tan. It is just as
well this screening process occurs because frequent and prolonged exposure of the skin to
ultraviolet radiation is associated with skin aging and increases the risk of developing certain
types of skin cancer (4).
2.2 Tissue damage by visible and near infrared radiation
Electromagnetic radiation in the wavelength range 400 - 1400 nm can damage the retina of
the eye by heating the tissue. This effect goes under the name of chorio-retinal injury. Such
injuries have a long history, mostly derived from looking directly at the sun for a prolonged
period. The main symptom of chorio-retinal injury is the presence of a "blind spot" or
scotoma in the area where the absorption occurred. The location of the injury is important. If
it occurs in the fovea, then it severely interferes with vision. If it is small and occurs in the
far periphery, it may pass unnoticed. Recovery from chorio-retinal injury is limited or non-
existent.
The above discussion has been concerned with thermal damage to the retina. Unfortunately,
there is also the possibility of rapid photochemical damage of the retina occurring following
exposure to visible wavelengths. This is called blue-light hazard or photoretinitis. The exact
nature of the chemical process by which photoretinitis occurs is not understood but what is
known is that it can occur at radiant energy levels less than those required to cause threshold
thermal damage Photoretinitis is rare in practice because the normal aversion to very bright
lights causes people to shield their eyes or to look away before damage can occur. However,
if exposure is sufficient to cause photoretinitis, the damage will not usually become apparent
until about twelve hours later. Some recovery is possible.
2.3 Tissue damage from infrared radiation beyond 1400 nm
Longer wavelength infrared radiation is absorbed in the cornea, aqueous humour and lens of
the eye. The absorbed energy raises the temperature of the tissue where it is absorbed and
may, by conduction, raise the temperature of adjacent areas. Fortunately, extremely high
corneal irradiances, of the order of 100 W/cm2, are necessary for changes in the lens to
occur within the time taken for the common aversive reaction to occur. Further, only 10
W/cm2 absorbed in the cornea will produce a powerful sensation of pain that should trigger
the aversive response.
As for the skin, the effect of visible and infrared radiation is simply to raise the temperature.
If the temperature elevation is sufficient then burns will be produced. It is important to
realize that the focusing process of the eye makes it much more sensitive than the skin to
such injury for visible radiation and near infrared radiation. However, the skin and eye are
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equally at risk from radiation beyond 1400 nm because the ocular media are virtually opaque
for these wavelengths and the mechanism for acute damage is thermal. The efficiency with
which a given irradiance raises the temperature of the skin depends on the exposed area, the
reflectance of the skin and the duration of exposure. The threshold irradiance for thermal
injury of the skin is greater than 1 W/cm2. Such irradiances are very unlikely to be produced
by sunlight or conventional lighting of interiors so such sources are unlikely to produce any
degree of thermal injury to the skin by radiation. In any case, for anything other than very
short exposure times, considerations of heat stress become relevant before thermal damage
can occur.
2.4 Threshold limit values
Given the potential for tissue damage by ultra-violet, visible and infra-red radiation, it
should not be too surprising that there are recommended limits to exposure to such radiation
(5,6,7). These threshold limit values are levels of exposure and conditions under which it is
believed, based on the best available scientific evidence, that nearly all healthy workers may
be repeatedly exposed, day after day, without adverse health effects (8). The threshold
limiting values take various forms depending on the size of the source of radiation and the
exposure time. For some situations, the threshold limit values are based on total irradiance at
the eye, while for others they are based on the spectral irradiance at the eye or the spectral
radiance of the source, multiplied by a weighting function based on the action spectrum of
the damage being controlled.
2.5 Hazardous light sources
The Illuminating Engineering Society of North America Recommended Practice 27 (7) sets
out a system for classifying light sources according to the level of radiation risk they
represent. This system has four classes; Exempt and Risk Groups 1, 2 and 3. Exempt light
sources are those that do not pose an ultra-violet hazard for eight hours of exposure, nor a
near ultra-violet hazard, nor an infra-red cornea / lens hazard within 1,000 seconds; nor a
retinal thermal hazard within 10 seconds, nor a blue-light hazard within 10,000 seconds. For
light sources where sound assumptions about typical use can be made, the radiometric
measurements necessary to evaluate the light source against these criteria are made at a
location where the light source is producing 500 lx, or at 20 cm from the light source if the
distance at which 500 lx is achieved is less than 20 cm. For light sources where sound
assumptions about use cannot be made, the necessary radiometric measurements are made at
a distance of 20 cm. Any light source that is assigned to Risk Groups 1, 2 or 3 must exceed
one or more of the criteria used for the Exempt Group. The philosophical basis for Risk
Group 1 (Low Risk) is that light sources in this group exceed the limits set for the Exempt
Group, but do not pose a hazard due to normal behavioural limitations on exposure. The
philosophical basis for Risk Group 2 (Moderate Risk) is that light sources in this group
exceed the limits set for the Exempt Group and Risk Group 1, but do not pose a hazard due
to the aversive response to very bright light or to thermal discomfort. Any light source in
Risk Group 3 (High Risk) is believed to pose a hazard, even for momentary exposures. The
criteria defining Risk Groups 1, 2 and 3 are the same as those for the Exempt Group but the
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permitted exposure times are reduced. Lamps falling into any of the Risk Groups should
carry a warning label, indicating the nature of the hazard and suggested precautions that
should be taken.
Table 1 Tissue damage classifications for a number of lamps used for general lighting (E =
Exempt Group; RG1 = Risk Group 1; RG2 = Risk Group 2; RG3 = Risk Group 3). All lamps
except the 500 W tungsten halogen were measured at the distance at which they produced
500 lx. The 500 W tungsten halogen lamp was measured at 20 cm (13)
Hazard 85 W
tungsten
halogen
500 W
tungsten
halogen
37 W
linear
fluoresce
nt
36 W
compact
florescen
t
400 W
mercury 360 W
high
pressure
sodium
150 W
compact
metal
halide
UV for eye
and skin E RG3 E E E E RG3
UV-A for eye
E E E E E E E
Chorio-
retinal burn E E E E E E E
Retinal blue
light E RG1 E E RG1 RG1 RG1
Infra-red eye
hazard
E RG2 E E E E E
Infra-red eye
hazard with
weak visual
stimulus
E RG3 E E E E E
Thermal
damage to
skin
E E E E E E E
Measurements of incandescent and fluorescent lamps commonly used for the lighting of
homes show that such light sources fall into the Exempt category and therefore are not a
hazard for tissue damage in normal conditions of use (9). This comprehensive evaluation is
consistent with the conclusions of other, more limited, studies of incandescent and
fluorescent lamps for ultraviolet radiation (10,11) and for photoretinitis (12). Table 1 shows
the classification of a wider range of light sources used for general lighting (13). Again, both
linear and compact fluorescent lamps fall into the Exempt Group for all criteria. The 85 W
tungsten halogen was also in the Exempt Group for all criteria but the 500 W tungsten
halogen was not, probably because the radiation was measured at only 20 cm from the lamp.
This may seem unrealistic but as the lamp falls into Risk Group 3 on two criteria, the lamp
does represent a hazard to people doing maintenance work on the luminaire. Other light
sources commonly used for lighting industrial and commercial buildings, such as high
wattage high pressure sodium, metal halide and mercury discharge lamps, all fall into Risk
Group 1 or 3 on one or more hazard criteria.
Figure 1 The relative spectral power distribution of a white light emitting diode (LED).
This is basically a blue LED with an integral phosphor.
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It is important to appreciate that these observations about the potential for tissue damage
posed by various light sources are generalizations. They should not be taken to apply to all
lamps of a given type. For example, while fluorescent lamps used for general lighting fall
into the Exempt Group, there are fluorescent lamps used for sunbeds and for germicidal
purposes that are designed to emit considerable ultra-violet radiation and that are not Exempt.
The safest principle to follow when evaluating the potential for tissue damage from any
specific light source is to assume the source is hazardous unless information suggesting
otherwise is available. This is particularly true for light emitting diodes (LEDs), a solid state
light source that is viewed by many as the future of lighting in buildings. LEDs that produce
the white light required for lighting in buildings are almost always a combination of a blue
LED and a yellow phosphor giving a two peaked spectrum (Figure 1). The problem is that
the blue peak falls close to the peak of the action spectrum for photoretinitis. The hazard
posed by LEDs used for lighting in buildings can be assessed using the photobiological
safety standard issued by the Commission Internationale de l’Eclairage (CIE) (6)
2.6 Practical considerations
The key word in the above discussion of the hazards posed by different light sources is
'potential'. Whether the potential for tissue damage turns into actual damage depends on how
the light source is used. The classification of a light source hazard used (7) assumes a bare
lamp viewed directly for a defined time. Light sources are normally used in luminaires, and
are rarely viewed directly for an extended period of time. Placing the light source in a
luminaire may dramatically change the spectrum of the radiation received by the viewer. For
example, the ultra-violet radiation emitted by tungsten halogen lamps can be much reduced
by using a glass cover. Dichroic reflectors can be used to transmit infrared radiation while
reflecting visible radiation. Different plastics and glasses have very different ultra-violet
transmittances. Another factor that will change the spectrum of the radiation received by the
viewer is what proportion of the radiation incident comes directly from the light source. The
larger is the proportion of radiation received after reflection, the more likely it is that the
spectral content will be changed, because there is no guarantee that the reflecting surface
reflects ultra-violet, visible and infra-red radiation equally. What this implies is that where
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there is doubt about the risk of tissue damage by radiation from light sources, field
measurements of the actual spectral radiance or irradiance are essential.
2.7 Ageing effects
In addition to the hazards of exposure to ultra-violet, visible and infra-red radiation
discussed above, there are also possible effects of such exposure on the rate at which ageing
progresses. One example is the possibility of a link between the total light exposure over life
and the likelihood of retinal damage. The proposed mechanism is that exposure to light
causes damage to the retina. This damage can be repaired but the repair mechanisms become
less effective with age, resulting in damage that accumulates more rapidly with greater
retinal exposure to light (14, 15). There is no doubt that the probability of retinal
deterioration increases with age, and there are close similarities between the changes
induced in the retina as a result of the ageing process and those elicited by exposure to high
levels of illumination (16), but whether it is really exposure to light that is responsible for
the ageing process in the retina remains open to question.
2.8 Conclusion
Although many of the effects of light as radiation on human health are well established, the
extent to which they occur in buildings is limited. The filtering of sunlight through glass or
plastic removes most of the ultraviolet radiation and some of the infrared radiation, the exact
amount depending on the chemical composition of the materials. The electric light sources
used in buildings produce little by way of hazardous radiation and when they do, they tend to
be placed in luminaires far above the places where humans are to be found. Even when
humans move close to such light sources, the aversion response to visual and thermal
discomfort is usually sufficient to ensure that exposure is limited. The one common form of
lighting where light as radiation has been identified as a hazard is the task light. Following
measurements of ultra-violet radiation from task lights fitted with tungsten halogen or
compact fluorescent light sources, the UK Health and Safety Executive recommend that the
use of task lights fitted with unfiltered tungsten halogen lamps for more than two hours a day
should be discouraged when the lights are within 0.6m of the user. Similarly, it is
recommended that the use of task lights fitted with single encapsulated CFLs should not be
allowed for longer than one hour at distances of less than 0.3m.
3. Light operating through the visual system
With light we can see, without it, we cannot. Light is a necessity for the visual system to
operate but if provided in the wrong way it can be injurious to health.
3.1 Eyestrain
The most common effect of lighting on health due to the operation of the visual system is
colloquially known as eyestrain. The symptoms of eyestrain are irritation of the eyes, evident
as inflammation of the eyes and lids; breakdown of vision, evident as blurring or double
vision; and referred effects, usually in the form of headaches, indigestion, giddiness etc.
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The symptoms of eyestrain are likely to appear whenever the viewer experiences
 Visual task difficulty, in which it is difficult to extract the required information from
the task,
 Under- or over-stimulation, in which the visual environment is such that it presents
too little or too much information,
 Distraction, in which the observer's attention is drawn to objects that do not contain
the information being sought,
 Perceptual confusion, in which the pattern of illuminance can be confused with the
pattern of reflectance in the visual environment.
These problems can be brought about either by poor lighting, the inherent features of the
task and its surroundings, inadequacies in the individual's visual system or some
combination of these factors. There are two mechanisms by which eyestrain can be caused,
one physiological and one perceptual. The physiological is muscular strain occurring in the
muscle systems that control the fixation, accommodation, convergence and pupil size of the
eyes. The perceptual is the stress that is felt when the visual system has difficulty in
achieving its primary aim, to make sense of the world around us. Conditions that require the
eye to be held in a fixed position for a long time or to make frequent movements of the same
type are likely to produce eyestrain through muscular exhaustion. Conditions that make it
difficult to see what needs to be seen or which distract attention from what needs to be seen
are likely to produce eyestrain through stress. Such conditions are likely to be described as
uncomfortable. The aspects of lighting that can cause visual discomfort and hence eyestrain
are too little light, too much light, too much variation in illuminance between and across
working surfaces, disability glare, discomfort glare, veiling reflections, shadows and flicker
(17). Despite this list, it is important to appreciate that in conditions where the task is
visually easy and free from visual discomfort, the visual system can function for many hours
without eyestrain. Carmichael and Dearborn (18) measured the eye movement patterns of
people continuously reading books printed in high contrast, 10-point print, for six hours, at
an illuminance of 160 lx, expecting to find signs of eyestrain. No such signs were found.
Apparently the visual system is perfectly capable of prolonged activity without strain in the
right conditions. Even when the conditions are not right, vision does not fail. Rather it
protests but will rapidly recover with rest.
There is a lot of guidance published on what are the right conditions for electric lighting in
buildings (1,2). Some of this advice is qualitative, e.g., for avoiding shadows and minimizing
flicker, while other advice is quantitative, e.g., limiting values for discomfort glare and
luminance ratios. There is rather less advice published for daylighting in building (19),
visual discomfort from windows being dealt with by obstruction of the sun or sky through
the use of external shields or canopies or internal light shelves or blinds.
3.2 Migraine
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Everyone is likely to experience eyestrain in poor lighting conditions but there are some
groups of people who are particularly sensitive to lighting conditions. One such group is
made up of those who suffer from migraines. A migraine attack is much more than a severe
headache. Nausea, vomiting, intolerance of smells and photophobia are all part of a migraine
attack. People who suffer from migraine are more sensitive to light than people who do not,
even when they are headache-free (20). This means people who suffer from migraines are
much more likely to experience glare from luminaires and to complain about high light
levels. In addition, they are likely to be hypersensitive to visual instability, no matter
whether it is produced by fluctuations in light output from a light source, or by large area,
regular patterns of very different reflectances (21,22). Whether large area, high contrast
regular patterns are present in an environment is usually the responsibility of the architect or
interior designer, but the presence of light output fluctuations are the responsibility of the
lighting designer.
Figure 2 Percentage of a sample of office workers experiencing different frequencies of
headaches per week, while working under fluorescent lighting operated on magnetic (50
Hz) control gear and electronic (32 kHz) control gear (after 23)
One way to ensure that light output fluctuations do not cause trouble is either to use light
sources that are inherently low in modulation, such as the incandescent lamp, or, if high
modulation discharge light sources are to be used, to operate them from high frequency
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control gear. Wilkins et al. (23) carried out a field study in an office of the effect of replacing
magnetic control gear operating from a 50 Hz electricity supply with electronic control gear
operating at 32 kHz, on the frequency of headaches and eyestrain. The fluorescent lighting
operating from the magnetic control gear had a modulation of about 45 percent at a
fundamental frequency of 100 Hz. The same lamps operating from the electronic control
gear had a modulation of less than 7 percent at 100 Hz. Figure 2 shows the percentage of the
occupants experiencing various frequencies of headaches per week when working under the
two types of fluorescent lighting. The distribution of headaches per week is strongly skewed.
This implies that everybody in the office gets a headache now and again, for all sorts of
reasons, but there a few people who experience headaches two or three times a week. Figure
2 demonstrates that changing from magnetic to electronic control gear does little for the
mass of people but does help the people who frequently have headaches. With the electronic
control gear nobody had a headache more frequently than 1.3 times per week. A similar
change occurred in the distribution of the frequency of eyestrain per week. Kuller and Laike
(24) report a similar pattern in that individuals who had a high critical flicker frequency
showed an increased arousal of the central nervous system when working under lighting
controlled from conventional 50 Hz control gear.
3.3 Autism
Another group who can be expected to be sensitive to fluctuations in light output are the
autistic. Autism is a neurological disorder that affects the ability to communicate, understand
language and relate to others. Symptoms are repetitive activities, stereotyped movements,
resistance to changes in the environment and the daily routine and unusual responses to
sensory experiences. The level of arousal of autistic children is chronically high and
repetitive behaviours are believed to be a way to regulate it (25). This implies that an
increase in environmental stimulation will generate an increase in repetitive behaviour and
regular fluctuations in light output can be regarded as a form of environmental stimulation.
Observations of autistic children have demonstrated that repetitive behaviour does occur
more frequently under fluorescent lighting than under incandescent lighting (26,27). This
suggests that autistics too would benefit from the use of electronic control gear for
fluorescent lamps. Care should also be taken to avoid lighting control systems that change
light levels suddenly.
3.4 Conclusion
There has been many years experience of designing lighting in buildings for the comfortable
operation of the visual system. This has resulted in numerous recommendations being
published to ensure that lighting does not cause visual discomfort. If these recommendations
are followed, the vast majority of people will not experience eyestrain. However, even if
these recommendations are followed eyestrain may still occur. The reason is that eyestrain is
caused by the visual environment and while lighting is a contributor to the visual
environment it is not the whole picture. The colours and reflectances of the surfaces
illuminated by the lighting are also important. It is also necessary to appreciate that while the
above is true for most people there are groups of people with enhanced sensitivity to some
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aspects of lighting. Where these people are likely to be present, the recommendations made
may need to be strengthened.
4. Light operating through the circadian system
Circadian rhythms are a basic part of life and can be found in virtually all plants and animals,
including humans. The human circadian system involves three components; an internal
oscillator, located in the suprachiasmatic nucleus in the brain; a number of external
oscillators that can reset (entrain) the internal oscillator, and a messenger hormone,
melatonin, which carries the internal "time" information to all parts of the body through the
bloodstream. In the absence of light, and other cues, the internal oscillator continues to
operate but with a period longer than twenty-four hours. External stimuli are necessary to
entrain the internal oscillator to a twenty-four hour period and to adjust for the seasons. The
light - dark cycle is one of the most potent of these external stimuli.
Figure 3 Predicted percentage human nocturnal melatonin suppression produced by
incandescent and daylight illuminances (lx) measured at the eye provided for 30
minutes and 60 minutes (after 31)
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000 10000
Illuminance (lx)
Incandescent / 30 mins
Incandescent / 60 mins
Daylight / 30 mins
Daylight / 60 mins
The amount of light required to form the light part of the light – dark cycle is measured by
the effect of light exposure on melatonin concentration. The spectral sensitivity revealed is
different from those of the visual system, having a peak sensitivity at about 470 nm. This
difference is due to the fact that the effect of light on the circadian system is primarily
mediated through a newly discovered photoreceptor located in the ganglion level of the
retina (28,29), although the cone photoreceptors used by the visual system are also involved.
Rea et al (30) have created a model of human phototransduction that enables the percentage
melatonin suppression due to the illuminance at the eye from a light source with a known
spectral power distribution to be calculated. Figure 3 shows the predicted percentage
nocturnal melatonin suppression achieved by exposure to different illuminances from
incandescent and D65 daylight for periods of 30 and 60 minutes using this model. Based on
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such data, Figueriro et al (31) suggest that an exposure of 30 lx at the eye for 30 minutes
should be taken as the threshold for white light to impact the circadian system. Of course,
this is a gross simplification, the actual threshold varying for individuals depending on their
previous history of light exposure and age (32, 33). Nonetheless, as a working hypothesis, it
has some interesting implications.
For a start, when compared with measurements of vertical illuminances in a range of
building types in the USA (31), it suggests that most commercial and industrial lighting is
sufficient to act as the light component of the light - dark cycle. Second, it suggests that
much residential lighting is insufficient for the purpose of stimulating the circadian system
and people who are confined to such interiors may effectively be living in biological
darkness. More importantly, it implies that people working night shifts in conventionally lit
industrial or commercial buildings and whose circadian system is not fully adjusted to
working at night will have their melatonin concentration reduced at the wrong time. There
are at least three consequences from such a reduction. First, there is an immediate alerting
effect that leads to better task performance (34). Second, there is the delayed effect of
shifting the phase of the circadian rhythm. Depending on when the light exposure occurs, the
phase can be advanced or delayed (17). Third, there is concern that the incidence and rate of
development of breast and other forms of cancer are increased when melatonin suppression
occurs night after night for a prolonged period (31).
The circadian system operates at a very fundamental level of human physiology. In
consequence, it can carry the effects far beyond those normally associated with light. Some
of those that have been extensively investigated are discussed below
4.1 Sleep
The sleep / wake cycle is one of the most obvious and important of the circadian rhythms.
People whose sleep is disturbed frequently feel permanently tired. There are a number of
common sleep disorders. Those susceptible to treatment with light are concerned with the
timing and duration of sleep. Those associated with timing are delayed and advanced sleep
phase disorders. Delayed phase sleep phase disorder is characterized by late sleep onset and
late awakening, and is predominantly experienced by the young.
Advanced phase sleep disorder is characterized by early sleep onset and early morning
awakening and is predominantly experienced by the elderly.
Exposure to light has been shown to be an effective treatment for these sleep disorders.
Czeisler et al. (35) have demonstrated that exposure to 10,000 lx at appropriate times results
in significant phase advances for people with delayed sleep phase disorder and significant
phase delay for those with advanced sleep phase disorder. The appropriate times are
immediately on awakening for the delayed sleep phase disorder and in the evening for the
advanced sleep phase disorder. Campbell et al. (36), in a study of elderly patients with
advanced sleep phase disorder, showed not only a phase delay following exposure to 4,000
lx in the evening but also an improvement in sleep quality.
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As for sleep duration disorders, the classic problems are sleep onset insomnia with normal
awakening and normal sleep onset with sleep maintenance insomnia. Both these disorders
are common in the elderly (37). It has also been shown that exposure to bright light in the
evening produces longer and better quality sleep for people who were experiencing sleep
maintenance insomnia (38, 39).
There can be little doubt that exposure to enough light at the right time is helpful in
promoting sleep, but what is enough light and what spectrum should the light have?
Unfortunately, there are no proven answers to these questions. A wide range of illuminances,
from 2,500 lx to 10,000 lx and a wide range of spectra, from fluorescent lamps to sunlight,
have been shown to be effective in the treatment of sleep disorders (40). Such high
illuminances are unrealistic for conventional building lighting but may well be the result of a
desire to guarantee a beneficial effect rather than necessary. Given that what is required is to
provide an effective light stimulus to the circadian system, it seems reasonable to suppose
that by matching the spectral emission of the light source to the spectral sensitivity of the
circadian system, a much lower illuminance could be used. Table 2 shows the calculated
ratio of circadian efficacy to luminous efficacy for a number of commercially available light
sources (31). The use of blue LEDs would allow the lowest illuminance to be used although
the risk of photoretinitis would need to be checked. If white light is required for reasons of
user acceptability, then either daylight or one of the very high colour temperature discharge
light sources would be most effective.
Table 2. The ratio of circadian to visual efficacies for a number of commercially available
light sources, the ratio being scaled so that the ratio for incandescent light source is unity (61)
Light source Circadian / visual ratio
4,100K Fluorescent 0.72
2,700K Fluorescent 0.73
Incandescent 1.00
3,000K Fluorescent 1.08
6,500K Daylight 2.07
8,000K Fluorescent 2.11
7,900K Metal halide 2.22
17,000K Fluorescent 3.84
Blue LED 17.60
4.2 Seasonally affective disorder
Depression is one of the most common psychiatric conditions in patients visiting a doctor,
with a lifetime prevalence of about 17 percent (41). Seasonally Affective Disorder (SAD) is
a subtype of major depression that is identified by a regular relationship between the onset of
depression and the time of year; full remission of depression at another time of year; the
pattern of onset and remission of depression at specific times of the year repeated over the
last two years; no non-seasonal depression over the last two years; and episodes of seasonal
depression substantially outnumbering non-seasonal depression over the individual's lifetime
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(42). Winter SAD is the most common form and can be recognized by the increase in
feelings of depression and a reduced interest in all or most activities, typical of depression,
together with such atypical symptoms as increased sleep, increased irritability and increased
appetite with carbohydrate cravings and consequent weight gain. These symptoms disappear
in Summer. Winter SAD is experienced by about 5 percent of the population and about 10 to
20 percent have sub-syndromal symptoms, the percentages increasing with an increase in
latitude (43, 44). Winter SAD is more common in females than males. Its prevalence
increases with age until about the sixth decade, after which it declines dramatically.
The cause of winter SAD is unknown. Explanations based on disturbances to the circadian
system and regulation of the hormone seratonin has been proposed but none have been
proven. While the cause of winter SAD is unclear, what is clear is that exposure to bright
light is often an effective treatment (45, 46, 47). What is meant by "bright light" is usually
exposure for one or two hours to a light box that produces an illuminance at the eye of
between 2,500 lx and 10,000 lx provided by fluorescent lamps. Again, such high
illuminances make it unrealistic to provide the necessary stimulation through conventional
building lighting apart from the provision of areas primarily lit by daylight. Where this is not
possible, it may be that by using light sources that are effective in stimulating the circadian
system, lower illuminances could be used. General guidance on the use of light in the
treatment of SAD is available from a number of sources (48, 49).
4.3 Alzheimer's disease
Alzheimer's disease is a degenerative disease of the brain and is the most common cause of
dementia. Lighting can influence the abilities and behaviour of people with Alzheimer's
disease, operating through both the visual system and the circadian system. Alzheimer's
patients show a reduced visual contrast sensitivity function relative to healthy people of the
same age (50). This pattern of change is consistent with the reports of cell loss at both retinal
and cortical level in Alzheimer's disease (51, 52). It has been argued that such reduced visual
capabilities may exacerbate the effects of other cognitive losses in Alzheimer's patients,
tending to increase confusion and social isolation. This suggests that enhancing the
luminance contrast of the stimulus would improve the functioning of Alzheimer's patients.
Gilmore et al. (53) have shown that increasing the luminance contrast does increase the
speed of letter recognition by Alzheimer's patients. This finding, suggesting as it does that
Alzheimer's patients are struggling to make sense of the world with diminished visual and
cognitive capabilities, raises the intriguing possibility that building lighting designed to
enhance the capabilities of people with low vision might also be effective in helping people
with Alzheimer's disease (17, 54).
As for the circadian system, people with Alzheimer's disease and other forms of dementia
often demonstrate fragmented rest / activity patterns throughout the day and night (55, 56).
This makes such patients difficult to care for and is one of the main reasons for having them
institutionalized. Degeneration is evident in the suprachiasmatic nucleus of people with
Alzheimer's disease (57) and such patients are less likely to be exposed to bright light (58).
This suggests that exposing Alzheimer's patients to bright light during the day and little light
at night, thereby increasing the signal strength for entrainment, would help to make their rest
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activity patterns more stable. Studies using light boxes of the type used for the treatment of
seasonal affective disorder (59), a general increase in room lighting (56) and localized blue
LED lighting (60) have shown the truth of this suggestion.
Recently, Figueiro (61) has proposed a 24 hour lighting scheme for older adults, particularly
those suffering from Alzheimer’s disease. The aims of this scheme are to provide high
circadian stimulation during the day and low circadian stimulation during the night, good
visual conditions during waking hours and nightlights that are safe for movement but that
minimize sleep disruption. The high circadian stimulation requires at least 400 lx of the eye
provided by a white light source rich in short wavelength light, such as daylight or
fluorescent lamps with a correlated colour temperature of 6,500K or higher. The low
circadian stimulation requires less than 100 lx at the eye from light sources with little short
wavelength light such as incandescents or 2,700 K fluorescents. The good visual conditions
can be ensured by following the recommendations made by many bodies to avoid glare,
shadows, veiling reflections and flicker. As for the nightlight, this should provide no more
than 5 lx at the cornea provided by a light source with little short wavelength light as well as
perceptual information that enables people to orient themselves relative to the vertical and
horizontal planes. Such information has been shown to improve postural stability (62)
4.4 Cancer
So far, all the examples of how light operating through the circadian system influences
human health have been positive but there is one that is undoubtedly negative. This is the
concern that exposure to light at night is involved with the incidence and development of
breast cancer. The incidence of breast cancer has increased continuously since the turn of the
twentieth century in industrialized societies (63). In 1987, it was suggested that the increase
could be at least partly ascribed to the suppression of melatonin following exposure to light
at night (64). Support for this hypothesis comes in two forms. The first is a series of
epidemiological studies that have shown that night shift work is associated with an increase
in breast cancer risk (65,66) and that blind women are at a lower risk of breast cancer than
sighted women (67). The second is the finding that melatonin-depleted blood increases the
rate of growth of breast cancer tumours (68). There is little doubt that repeated exposure to
sufficient light to suppress melatonin from its normal concentration has some role to play in
the incidence and development of breast cancer but there may be other necessary conditions
yet to be established (31, 69).
The implications of what we know so far about the effect of light exposure on breast cancer
for the lighting of buildings is rather limited. Given that melatonin suppression is necessary
for any adverse effects to occur and the threshold for melatonin suppression is about 30 lx at
the eye for 30 minutes (31), the amount of light present when people are trying to sleep or
when briefly visiting the bathroom at night is not a problem. However, the illuminances
provided in commercial and industrial premises for visual purposes where people are
working whose circadian rhythm is not fully adapted are likely to be a cause for concern.
One possible solution to the dilemma of providing sufficient light to enable the visual system
to operate effectively while avoiding melatonin suppression would be to use light with a
spectrum rich in long wavelength light and deficient in short wavelength light, i.e.,
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mismatched to the spectral sensitivity of melatonin suppression. Such an approach would be
a wise course to take for the lighting of night shift work until the role of light at night on
breast cancer and possible other forms of cancer is clarified.
4.5 Conclusion
Unlike the visual system where the impact of light is immediate and obvious, the effect of
light on the circadian system has a long time constant and is a relatively recent area of study
(70). As a result there are several important questions that remain to be answered before
light operating through the circadian system can be deliberately used in the lighting of
buildings (71). Among them are the relative sensitivity of different parts of the visual field;
whether it is the ratio of the light to dark periods that matter; and, most importantly, what
affect does light exposure have, if any, on the health of those who live a conventional diurnal
life? There is some evidence that variations in the amount and spectrum of light exposure
during the day can increase the alertness and feelings of vitality of people living a normal
diurnal life (72,73) but what mechanism is involved and how such feelings might impact
health in the long term is not yet known.
Figure 4 Schematic diagram of eye-brain pathways. Light received by the eye is
converted to neural signals that pass via the optic nerve to two pathways, one visual and
one non-visual. RHT = Retino-hypothalamic tract. IGL = Intergeniculate leaflet. SCN
= Suprachiasmatic nucleus of the hypothalamus. PVN = Paraventricular nucleus of the
hypothalamus. IMLCC = Intermediolateral cell column. SCG = Superior cervical
ganglion. CRH = Corticotropic releasing hormone. ACTH = adrenocorticotropic
hormone (from 70).
5. Implications
Exposure to light can have both positive and negative impacts on human health, impacts that
can become evident soon after exposure or only after many years. The luminous conditions
likely to be negative for health from light as radiation and from light operating through the
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visual system are well established. As a consequence, standards have been written to
minimize the probability of harm occurring and lighting practice takes them into account
The same cannot be said for light operating through the circadian system. That exposure to
light does influence the operation of the circadian system is undeniable but the
suprachiasmatic nucleus is connected many other parts of the brain (Figure 4). These
regulate the production of many hormones so light may have an impact on aspects of human
physiology beyond the circadian system (74). There is also a positive effect of light as
radiation. Vitamin D is synthesized in the body by exposure to ultra-violet radiation.
Insufficient vitamin D is known to be linked to bone disorders but it is also associated with a
higher risk of such scourges as multiple sclerosis, diabetes, tuberculosis and many forms of
cancer (75).
Clearly there is still much to learn about the non-visual effects of light exposure (70, 76).
Nonetheless, it is already possible to identify two general implications for the lighting of
buildings. The first is that the lighting of buildings should no longer be considered solely in
terms of the effects on visual capabilities. The second is that the spectral content of daylight
is well suited to stimulate both the visual and the non-visual systems. Both the visual system
and the non-visual systems have evolved under daylight. The alternative electric light
sources have only been available for about a hundred years, a very short time in evolutionary
terms. It may be that the main impact of a greater understanding of the role of light exposure
in human health will be to return attention to the better daylighting of buildings.
References
1. Chartered Institution of Building Services Engineers, Code for Lighting, London, CIBSE,
2006.
2. Illuminating Engineering Society of North America, The IESNA Lighting Handbook, 9th
Edition, New York, IESNA, 2000.
3. Pitts DG, Tredici TJ: The effects of ultraviolet on the eye: Am. Ind. Hyg. Assoc 1971;
32:235-246.
4. Freeman RG, Hudson HT, Carnes R: Ultra-violet wavelength factors in solar radiation and
skin cancer, Int J Dermatology 1970; 9:232-235.
5. American Conference of Governmental Industrial Hygienists: TLVs and BEIs Threshold
Limit Values for Chemical Substances and Physical Agents, Biological Exposure Indices,
Cincinnati, ACGIH, 2009.
6. Commission Internationale de l”Eclairage: CIE Standard S009/E-2002 Photobiological
Safety of Lamps and Lamp Systems. Vienna, CIE, 2002.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
17

7. Illuminating Engineering Society of North America: ANSI/IESNA RP-27-96,
Recommended Practice for Photobiological Safety for Lamps and Lamp Systems, New York,
IESNA, 1996.
8. Sliney DH, Bitran M: The ACGIH action spectra for hazard assessment: The TLV's; in
Matthes R, Sliney D (eds): Measurements of Optical Radiation Hazards, OberschleiBheim,
Germany, International Commission on Non-Ionizing Radiation Protection, 1998.
9. Wood Jr RL, Franks JK, Sliney DH: Measurements of representative lamps for the
ANSI/IESNA RP-27.3-96 photobiological safety standard for lamps, in Matthes R, Sliney D
(eds): Measurements of Optical Radiation Hazards, OberschleiBheim, Germany:
International Commission on Non-Ionizing Radiation Protection, 1988.
10. McKinlay AF, Harlen F, Whillock MJ: Hazards of Optical Radiation, Bristol, UK, Adam
Hilger, 1988.
11. Bergman RS, Parham TG, McGowan TK: UV emission from general lighting lamps,
Journal of the Illuminating Engineering Society 1995; 24:13-24.
12. Bullough JD: The blue-light hazard: A review, Journal of the Illuminating Engineering
Society 2000; 29:6-14.
13. Kohmoto K: Evaluation of actual light sources with proposed photobiological lamp safety
standard and its applicability to guide on lighted environment, Proceedings of the CIE, 24th
Session, Warsaw: Vienna, CIE, 1999.
14. Marshall J: Light damage and the practice of ophthalmology; in Rosen E, Arnott E,
Haining W (eds): Intraocular Lens Implantation, London: Moseby-Yearbook, 1981..
15. Young RW: (1981) A theory of central retinal disease; in Sears ML (ed): New Directions
in Ophthalmic Research, New Haven, CT: Yale University Press, 1981.
16. World Health Organization: Lasers and Optical Radiation, Environmental Health Criteria
Document 23. Geneva, WHO, 1982.
17. Boyce PR: Human Factors in Lighting. London, Taylor and Francis, 2003
18. Carmichael L, Dearborn WF: (1947) Reading and Visual Fatigue. Westport, CT,
Greenwood Press, 1947.
19. British Standards Institution: BS 8206-2:2008 Lighting for Buildings – Part 2: Code of
Practice for Daylighting. London, BSI, 2008.
20. Main A, Dowson A, Gross M: Photophobia and phonophobia in migraineurs between
attacks: Headache 1997: 376:492-495.
21. Marcus DA, Soso MJ: Migraine and stripe-induced visual discomfort: Arch Neurol 1989;
46:1129-1132.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
18

22. Wilkins AJ: Visual Stress, Oxford, Oxford University Press, 1995.
23. Wilkins AJ, Nimmo-Smith I, Slater AJ, Bedocs L: Fluorescent lighting, headaches and
eyestrain: Lighting Research and Technology 1989; 21:11-18.
24. Kuller R, Laike T: The impact of flicker from fluorescent lighting on well-being,
performance and physiological arousal: Ergonomics 1998; 41:433-447.
25. Hutt C, Hutt S, Lee D, Ounsted C: Arousal and childhood autism: Nature 1964; 204:908-
909.
26. Colman RS, Frankel F, Ritvo E, Freeman BJ: The effects of fluorescent and incandescent
illumination upon repetitive behaviors in autistic children: Journal of Autism and Childhood
Schizophrenia 1976; 6:157-162.
27. Fenton DM, Penney R: The effects of fluorescent and incandescent lighting on the
repetitive behaviours of autistic and intellectually handicapped children: Australia and New
Zealand Journal of Developmental Disabilities 1985; 11:137-141.
28. Brainard GC, Hanifin JP, Greeson, JM, Byrne B, Glickman G, Gerner E, Rollag MD:
Action spectrum for melatonin regulation in humans: Evidence for a novel circadian
photoreceptor: J Neuroscience 2001; 21:6405-6412.
29. Thapan K, Arendt J, Skene DJ: An action spectrum for melatonin suppression: Evidence
for a novel non-rod, non-cone photoreceptor system in humans: J Physiol 2001; 535:261-267.
30. Rea MS, Figueiro MG, Bullough JD, Bierman A: A model of phototransduction by the
human circadian system: Brain Res Rev 2005; 50:213-228.
31. Figueiro MG, Rea MS. Bullough JD: Does architectural lighting contribute to breast
cancer?: J. Carcinogenesis 2006; doi 1186/1477-3163-5-20
32. Hebert M, Martin SK, Lee C, Eastman CI: The effects of prior light history on the
suppression of melatonin by light in humans: J. Pineal Res 2002; 33:198-203.
33.Smith KA, Schoen MW, Czeisler CA: Adaptation of human pineal melatonin suppression
by recent photic history: J. Clin. Endocrinol. Metab 2004; 89:3610-3614.
34. Cajochen C, Zeitzer JM, Czeisler CA. Dijk, D-J: Dose-response relationship for light
intensity and ocular and electroencephalographic correlates of human alertness: Behav Brain
Res 2000; 115:75-83.
35. Czeisler CA, Kronauer RE, Johnson MP, Allen JS, Dumont M: Action of light on the
human circadian pacemaker: Treatment of patients with circadian rhythm sleep disorders, in
Horn J (ed) Sleep '88. Stuttgart, Germany: Verlag, 1988.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
19

36. Campbell SS, Dawson D, Anderson MW: Alleviation of sleep maintenance insomnia
with timed exposure to bright light: J Am Geriartr Soc 1993; 41:829-836.
37. Foley DJ, Monjan AA, Brown SL, Simonsick EM, Wallace RB, Blazer DG: Sleep
complaints among elderly persons: An epidemiologic study of three communities: Sleep
1995; 18:425-432.
38. Campbell SS, Dawson D: Bright light treatment of sleep disturbance in older subjects:
Sleep Res 1991; 20:448.
39. Lack L, Schumacher K: Evening light treatment of early morning insomnia: Sleep Res
1993; 22:225.
40. Terman M, Lewy AJ, Dijk D-J, Boulos Z., Eastman CI, Campbell SS: Light treatment for
sleep disorders: Consensus report. IV. Sleep phase and duration disturbances: J Biol Rhythms
1995; 10:135-147.
41. Kessler RC, McGonagle KA., Zhao S, Nelson CB, Hughes M, Eshleman S: Lifetime and
12-month prevalence of DSM-III-R psychiatric disorders in the United States: Arch. Gen.
Psychiatry 1994; 51:8-19.
42. American Psychiatric Association (APA): Diagnostic and Statistical Manual of Mental
Disorders, DSM-IV-TR: Washington DC, APA, 2000.
43. Kasper S, Rogers SLB, Yancey A, Schulz PM, Skwerer RG, Rosenthal NE: Phototherapy
in individuals with and without subsyndromal seasonal affective disorder: Arch. Gen.
Psychiatry 1989; 46:837-844.
44. Wehr TA, Rosenthal NE: Seasonality and affective illness, Am. J. Psychiatry 1989;
146:829-839.
45. Rosenthal NE, Sack DA, James SP, Parry BL, Mendelson WB, Tamarkin L, Wehr TA.:
Seasonal affective disorder and phototherapy; in Wurtman RJ, Baum MJ, Potts Jr JT (eds):
The Medical and Biological Effects of Light, New York, New York Academy of Sciences,
1985.
46. Terman M, Terman JS, Quitkin FM, McGrath PJ, Stewart JW, Rafferty B: Light therapy
for seasonal affective disorder: A review of efficacy: Neuropsychopharmacology 1989; 2:1-
22.
47. Tam EM, Lam RW, Levitt AJ: Treatment of seasonal affective disorder: a review: Can. J.
Psychiatry 1995; 40:457-466.
48. Saeed SA, Bruce TJ: Seasonal affective disorders: Am. Fam. Physician 1998; 57:1340-
1346, 1351-1352.
49. Lam RW, Levitt AJ: Canadian Consensus Guidelines for the Treatment of Seasonal
Affective Disorder. Vancouver, Clinical and Academic Publishing, 1999.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
20

50. Gilmore GC, Whitehouse PJ: Contrast sensitivity in Alzheimer's disease: A 1-year
longitudinal analysis: Optometry and Vision Science 1995; 72:83-91.
51. Blanks JC, Torigoe Y, Hinton DR, Blanks RHI: Retinal degeneration in the macula of
patients with Alzheimer's disease: Ann NY Acad Sci 1991; 640:44-46.
52. Kurylo DD, Corkin S, Schiller PH, Golan RP, Growdon JH: Disassociating two visual
systems in Alzheimer's disease: Invest Ophthal Vis Sc 1991; 32:1283.
53. Gilmore GC, Thomas CW, Klitz T, Persanyi MW, Tomsak R: Contrast enhancement
eliminates letter identification speed deficits in Alzheimer's disease: J Clin Geropsychology
1996; 2:307-320.
54. RNIB and Thomas Pocklington Trust: Improve the Lighting of Your Home. London,
RNIB and Thomas Pocklington Trust, 2009.
55. Aharon-Peretz J, Masiah A, Pillar T, Epstein T, Tzichinsky O. Lavie P: Sleep-wake
cycles in multi-infarct dementia and dementia of the Alzheimer type, Neurology 1991;
41:1616-1619.
56. Van Someren EJW, Hagebeuk EEO, Lijzenga C, Schellens P, Rooij S. Eja DE, Jonker C,
Pot MA, Mirmiran M, Swaab D: Circadian rest-activity rhythm disturbances in Alzheimer's
disease: Biol. Psychiatry 1996; 40:259-270.
57. Swaab DF, Fliers E, Partiman T.S: The suprachiasmatic nucleus of the human brain in
relation to sex, age and senile dementia: Brain Research 1985; 342:37-44.
58. Campbell SS, Kripke DF, Gillin JC, Hrubovcak JC: Exposure to light in healthy elderly
subjects and Alzheimer's patients: Physiol Behav 1988; 42:141-144.
59. Lovell BB, Ancoli-Isreal S, Gevirtz R: Effect of bright light treatment on agitated
behavior in institutionalized elderly subjects: Psychiatry Research 1995; 57:7-12.
60. Figueiro MG, Rea MS: Improving the sleep quality of older adults. Proceedings of the
CIE Midterm Meeting and International Lighting Congress, Leon Spain, Vienna, CIE, 2002.
61.Figueiro MG: A proposed 24h lighting scheme for older adults: Lighting Research and
Technology 2008; 40:153-160.
62. Figueiro MS, Gras L, Qi R, Rizzo P, Rea M, Rea MS: A novel night lighting system for
postural control and stability in seniors: Lighting Research and Technology 2008; 40:111-
126.
63. Chu KC, Tarone RE, Kessler LG, Ries LA., Hankey BF, Miller BA, Edwards BK: Recent
trends in U.S. breast cancer incidence, survival and mortality rates: J. Natl. Cancer Inst 1996;
88:1571-1579.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
21

64. Stevens RG: Electric power use and breast cancer: a hypothesis, Am. J. Epidemiol 1987;
125:556-561.
65. Hansen J: Light at night, shiftwork and breast cancer risk: Natl Cancer Inst 2001;
93:1513-1515
66. Davis S, Mirick DK, Stevens RG: Night shift work, light at night and risk of breast
cancer: J. Natl. Cancer Inst 2001; 93:1557-1562.
67. Feychting M, Osterlund B, Ahlbom A.: Reduced cancer incidence among the blind:
Epidemiology 1998; 9:490-494.
68. Blask DE, Brainard GC, Dauchy RT, Hanifin JP, Davidson LK, Krause JA, Sauer LA,
Rivera-Bermudez MA, Dubocovich ML, Jasser SA., Lynch DT, Rollag MD, Zalatan F:
Melatonin-depleted blood from premenopausal women exposed to light at night stimulates
growth of human breast cancer xenografts in nude rats: Cancer Research 2005; 65:11174-
11184.
69. Schernhammer ES, Kroenke CH, Laden F, Hankinson SE: Night work and risk of breast
cancer: Epidemiology 2006; 17:108-111.
70. Commission Internationale de l'Eclairage : CIE Report 158:2004 Ocular Lighting Effects
on Human Physiology and Behaviour. Vienna, CIE, 2004.
71. Boyce PR: Lemmings, light and health: Leukos 2006; 2:175-184.
72. Partonen T, Lönnqvist J : Bright light improves vitality and alleviates distress in healthy
people: J Affective Disorders 2000; 57:55-61.
73. Noguchi H, Ito T, Katayama S, Koyama E, Morita T, Sato M: Effects of bright light
exposure in the office: Proceedings of the CIE Expert Symposium on Light and Health (CIE
x27:2004) Vienna, CIE, 2004.
74. Hastings MH, Reddy AB, Maywood ES: A clockwork web: circadian timing in brain and
periphery, in health and disease: Nature Rev Neuro, 2003:4:649-661.
75. Garland CF, Garland FC, Gorham ED: The role of vitamin D in cancer prevention: Amer
J Pub Health 2006; 96:252-261.
76. Brainard GC, Hanafin JP: Photons, clocks and consciousness, J Biol Rhythms 2005;
20:314-325.
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The Impact of Light inThe Impact of Light in
The Impact of Light in
Buildings on Human Health
The Impact of Light in
Buildings on Human Health
Peter R Bo ce
Peter R Bo
y
ce
Professor Emeritus
Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute
Light and healthLight and health
•The impact of light
exposure on human
health and well-being
is a topic of great
interest but our
knowledge ranges
knowledge ranges
from the real to the
fanciful - what do we
really know?
really know?
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DefinitionsDefinitions
•Health - A state of complete physical,
mental and social well
-
being and not
mental and social well
being and not
merely the absence of disease and
infirmity - WHO
•Well-being - A good or satisfactory
condition of existence; a state
characterized by health happiness and
characterized by health
,
happiness and
prosperity - Webster’s
DefinitionsDefinitions
•The problem with these definitions is
that they are so wide as to be
meaningless
•
With these definitions there is hardly
•
With these definitions
,
there is hardly
any aspect of life that cannot be said to
influence health and well-being, lighting
bi j t t
b
e
i
ng
j
us
t
one amongs
t
many
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Alternative definitionAlternative definition
•Health - the absence of disease and
infirmity
•This definition places responsibility for
studying light and health where it
studying light and health where it
belongs, with the medical profession
Alternative definitionAlternative definition
•Well-being - a state of existence
characterized by health, happiness and
prosperity
prosperity
•This definition means that the study of light
and well
-
being should involve psychologists,
and well
being should involve psychologists,
sociologists, economists and politicians as
well as the medical profession
•This makes it important when discussing well-
being to be clear about what is meant in any
specific context
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Other definitionsOther definitions
•Buildings - structures within which people are likely to
spend prolonged periods, e.g, homes, offices,
factories
•Light - ultra-violet, visible, and infrared radiation
•
Lighting
natural or electric lighting designed to
•
Lighting
-
natural or electric lighting designed to
enable people to see. This excludes light used for
industrial or medical purposes
•People - the healthy and those groups whose
medical condition makes them sensitive to light
exposure
Established effects of light
on human health
Established effects of light
on human health
•Exposure to light can have both positive and
ne
g
ative effects on health
,
soon after
g,
exposure or only after many years. These
effects occur through three routes
•Light as optical radiation
•Light operating through the visual system
•Light operating through the circadian
system
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Light as optical radiationLight as optical radiation
Can cause tissue damage to the eye and
the skin both acute and chronic
the skin
,
both acute and chronic
Can generate vitamin D
Can generate vitamin D
Can be used in phototherapy for specific
ill
ill
nesses
Tissue damageTissue damage
•Damage to the eye
•Photokerititis
Ct t
•
C
a
t
arac
t
•Chorio-retinal burns
•Blue-light hazard
(Photoretinitis)
(Photoretinitis)
•Damage to the skin
Eth d b
•
E
ry
th
ema an
d
sun
b
urn
•Skin aging
•Burns
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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PhotokeratitisPhotokeratitis
PhotokeratitisPhotokeratitis
•A delayed inflammation
of the cornea of the eye
•A photochemical
reaction
•Painful but temporary
•Action spectrum peaks
at 270 nm
PhotoretinitisPhotoretinitis
•Photoretinitis (or blue-
light hazard) is rapid
photochemical damage
to the retina
•The action spectrum
shows much
g
reater
g
sensitivity in the short
wavelength visible
•
The aversion response
•
The aversion response
usually avoids damage
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Erythema and
b
Erythema and
b
sun
b
urnsun
b
urn
•Delayed, short term
photochemical effect on
th ki
th
e s
ki
n
•Action spectrum peaks
about 290 nm
•Repeated exposure
leads to tanning, i.e.,
skin thickening and
skin thickening and
ageing
Threshold limit valuesThreshold limit values
•To determine if a lighting condition has the
potential to cause tissue damage, threshold
limit values are published by various national
limit values are published by various national
and international bodies (ACGIH, IESNA, CIE)
•
Threshold limit values should not be
Threshold limit values should not be
exceeded over normal periods of exposure
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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29

Threshold limit valuesThreshold limit values
•To assess if a light source will exceed the threshold limit
value multi
p
l
y
the o
p
tical radiation s
p
ectrum of the li
g
ht
py p p g
source by the action spectrum of the effect and sum
over all wavelengths .
Hazardous light sourcesHazardous light sources
•IESNA has system for classifying light
sources producing 500 lx at site or at 20
cm (RP27)
cm (RP27)
•Exempt = No hazard
•No UV hazard for 8 hours exposure
•No retinal burn hazard within 10 s
•No photoretinitis hazard within 10,000 s
•No IR hazard within 1000 s
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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30

Hazardous light sourcesHazardous light sources
•Risk group 1 = Exceed exempt group but hazard
limited by normal behaviour reducing exposure
•Risk group 2 = Exceed exempt group and risk
group 1 but hazard limited by aversive response
•Risk group 3 = Hazardous even for momentary
exposure and not limited by normal behaviour or
aversive res
p
onse
p
Hazardous light sourcesHazardous light sources
•Exempt: 85W tungsten halogen, 37W linear fluorescent
for general lighting, 36W CFL
•Risk group 1: 500W tungsten halogen, 360W high
pressure sodium, 150W metal halide (photoretinitis)
•
Risk group 2: 500W tungsten halogen (chorio
retinal
•
Risk group 2: 500W tungsten halogen (chorio
-
retinal
burn)
•Risk group 3: 500W tungsten halogen, 150W metal
halide (photokeratitis, erythema)
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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Hazards in practiceHazards in practice
•Windows, luminaires
and reflecting surfaces
in buildings can all
in buildings can all
change the amount
and spectrum of light
exposure produced by
li ht
a
li
g
ht
source
•The distances from the
light source are usually
light source are usually
increased
Light hazards in buildingsLight hazards in buildings
•Lighting designed for
vision is rarely a radiation
hazard in buildings
•The most likely situation
for radiation hazard to
occur is a task li
g
ht fitted
g
with a tungsten halogen or
CFL light source. This
hazard can be easily
avoided by filtering out
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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32

A coming hazardA coming hazard
•Light emitting diodes
(LEDs) are increasing
rapidly in power and use
for lighting
•White LEDs have a strong
p
eak at short visible
p
wavelengths
•The blue-light radiation
hazard from these needs
hazard from these needs
to checked as they are
applied
Light operating through the visual
s
y
stem - e
y
estrain
Light operating through the visual
s
y
stem - e
y
estrain
y
y
y
y
•Symptoms are
inflammation of the
eyes tearing failing
eyes
,
tearing
,
failing
vision, and
headaches
•Anyone who
experiences these
regularly is not
enjoying good
enjoying good
health
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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Causes of eyestrainCauses of eyestrain
•Physiological - overuse of
muscles controlling the eye
•
Perceptual
-
conditions that
Perceptual
conditions that
make it difficult to see what
needs to be seen or that
cause distraction or
confusion
confusion
Avoiding eyestrainAvoiding eyestrain
•Make tasks visually easy
Follow authoritative
•
Follow authoritative
guidance for lighting
•
Features of lighting that
Features of lighting that
cause visual discomfort
are well understood and
easily avoided
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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Special case - migraineSpecial case - migraine
•Migraineurs are much more
sensitive to glare and
flicker than others
•Migraineurs are also
sensitive to large area
stri
p
ed
p
atterns
pp
•Believed to be caused by
hyperexcitability in the
visual cortex
visual cortex
Special case - migraine
(Wilkins et al, 1989)
Special case - migraine
(Wilkins et al, 1989)
•To minimize the risk of
migraine:
•Use low modulation light
sources
•
Use high frequency control
•
Use high frequency control
gear
•Avoid high contrast, large
area, regular patterns
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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Special case - autismSpecial case - autism
•Autism is a neurological disorder
•S
y
m
p
toms are re
p
etitive activities
,
stereot
yp
ed
yp p , yp
movements, and resistance to changes in the
environment and routine
•
Repetitive behaviour occurs more frequently under
Repetitive behaviour occurs more frequently under
fluorescent lighting than incandescent (Fenton and
Penny, 1985)
Autistics would probably benefit from the use of high
•
Autistics would probably benefit from the use of high
frequency control gear and the use of dimming rather
than switching controls
Light operating through the
circadian s
y
stem
Light operating through the
circadian s
y
stem
yy
•The circadian system
provides timing of
provides timing of
many bodily activities,
most notably, the sleep
/ wake c
y
cle
y
•Exposure to a light /
dark cycle entrains the
dark cycle entrains the
circadian system
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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36

Sleep disordersSleep disorders
•Exposure to bright light at the right time
can help people with advanced and
delayed sleep phase disorder (Terman
delayed sleep phase disorder (Terman
et al, 1995)
•The right times are in the evening for
the advanced sleep phase disorder and
immediately on awakening for the
dl d l di d
d
e
l
aye
d
s
l
eep
di
sor
d
e
r
Seasonally affective disorderSeasonally affective disorder
•Exposure to bright light is
effective in alleviating
i t SAD (T t l
w
i
n
t
er
SAD (T
am e
t
a
l
,
1995)
•Li
g
ht can be b
y
da
y
li
g
ht or
gyyg
by light boxes, providing
10,000 lx for 30 minutes
•
Side effects of such light
Side effects of such light
exposure can be
headaches and mania
(Kogan and Guilford, 1998)
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
37

Alzheimer’s disease
(Van Someren et al, 1996)
Alzheimer’s disease
(Van Someren et al, 1996)
•Alzheimers patients
often have fractured
sleep / wake
sleep / wake
patterns
•
Bright light during
Bright light during
the day and dim
light at night can
improve the
structure of the
structure of the
sleep / wake cycle
Alzheimer’s disease
(Gilmore and Whitehouse, 1995)
Alzheimer’s disease
(Gilmore and Whitehouse, 1995)
•Alzheimer’s patients
have worse vision than
healthy people of the
same age
•Lighting designed to
im
p
rove the visual
p
capabilities of people
with partial sight may
also help those with
Alzheimers disease -
high contrast on salient
information
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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38

Light at night and breast cancerLight at night and breast cancer
•The prevalence of breast cancer has been increasing
steadily in industrialized societies (Chu et al, 1996)
•It is hypothesized that exposure to light at night resulting
in a suppression of melatonin is linked to the incidence of
breast cancer (Stevens, 1987)
•There is epidemiological support for the link between
night shift work and breast cancer (Hansen, 2001;
Schernhammer et al, 2006)
•There is some evidence for the effect of melatonin
suppression on tumour growth (Blask et al, 2005)
What do we know?What do we know?
•Our knowledge of the effects of light on health
when considered as optical radiation, and of light
operating through the visual system is extensive
operating through the visual system is extensive
.
As a result, lighting designed to current standards
poses little hazard
•Our knowledge of light operating through the
circadian system is limited
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
39

What do we know?What do we know?
•How limited our knowledge of the circadian
system is can be made evident by considering
•
Fundamental questions
•
Fundamental questions
•Questions of efficiency
Answers to questions in both areas are needed to
•
Answers to questions in both areas are needed to
ensure safe, efficient and effective use of light in
buildings for human health
Fundamental questions -
connections
Fundamental questions -
connections
•The suprachiasmatic nucleus is connected to
many other parts of the brain. What effects do
these connections have?
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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40

Fundamental questions -
robustness
Fundamental questions -
robustness
•Is the circadian system
robust or delicate?
•If it is robust, the exact
lighting conditions are
unimportant
•If it is delicate then the
lighting conditions need
to be carefully tuned
to be carefully tuned
Questions of efficiencyQuestions of efficiency
•Questions of efficiency relate to
•What is the spectral sensitivity?
•How much light is needed?
•Are all points of the retina equally sensitive?
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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41

Spectral sensitivitySpectral sensitivity
•Spectral sensitivity based
on single wavelengths
shows a peak at about
470 nm (Brainard et al,
2001 Th t l 2001)
2001
.
Th
apan e
t
a
l
,
2001)
•Evidence for opponency
with multiple wavelen
g
ths
g
(Figueiro et al, 2004)
•
There is a model of
•
There is a model of
phototransduction (Rea et
al, 2005)
Circadian / visual
stimulation ratios (Figueiro, 2008)
Circadian / visual
stimulation ratios (Figueiro, 2008)
Light source Circadian / Visual ratio
4,100K fluorescent 0.72
2 700K fl t
073
2
,
700K fl
uorescen
t
0
.
73
Incandescent 1.00
3,000K fluorescent 1.08
6 500K fl t
207
6
,
500K fl
uorescen
t
2
.
07
8,000K fluorescent 2.11
7,900K metal halide 2.22
17 000K fl t
384
17
,
000K fl
uorescen
t
3
.
84
Blue LED 17.60
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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42

AmountAmount
•Bright light as used is often 1000s of lux. This is
done not because it is known to be necessary
but because it is certain to produce an effect
but because it is certain to produce an effect
•Predicted percentage melatonin suppression
f
data indicates that 30 lx at the eye
f
or 30
minutes of white light is the threshold (Figueiro
et al, 2006)
Amount
(Figueiro et al, 2006)
Amount
(Figueiro et al, 2006)
80
90
100
40
50
60
70
80
Incandescent / 30 m
i
Incandescent / 60 m
i
Daylight / 30 mins
10
20
30
40
Daylight / 60 mins
0
0.1 1 10 100 1000 10000
Illuminance (l
x
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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43

AmountAmount
•If this is correct it suggests that
St lihti bd d ihtliht t
•
St
ray
li
g
ht i
n
b
e
d
rooms an
d
n
i
g
htli
g
ht
s are no
t
a
problem for health
•Illuminances in commercial, industrial and health
buildings where people work at night are sufficient to
suppress melatonin
•
Until the consequences are clear, it would be better to
Until the consequences are clear, it would be better to
use light sources with little short wavelength light in
such buildings at night
Retinal sensitivityRetinal sensitivity
•Lower half of retina produces greater suppression of
melatonin than the upper (Glickman et al, 2003)
•This has implications for light distribution for circadian
stimulation
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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44

The billion dollar questionThe billion dollar question
•Established effects of
light on health when
operating through the
circadian system are for
people who are ill or
who live under an
unusual light profile
•Does light have
beneficial effects on the
healthy, who work by
day and sleep by night?
Light and health - summaryLight and health - summary
Light can have both positive and negative
effects on human health
For most people, their normal exposure to light
is unlikely to cause tissue damage. However,
some people are very sensitive to light and need
to take care
to take care
Extensive guidance is available on the
avoidance of tissue damage
avoidance of tissue damage
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
9 October 2009
45

Light and health - summaryLight and health - summary
Bdlihti ti th hth i l
B
a
dli
g
hti
ng, opera
ti
ng
th
roug
hth
e v
i
sua
l
system, can cause eyestrain and headaches
Autistics and migraineurs are sensitive to any
Autistics and migraineurs are sensitive to any
instability in the lighting
Light operating through the circadian system
Light operating through the circadian system
can impact the timing of the sleep / wake cycle
and many other physiological functions
Light and health - summaryLight and health - summary
Light exposure can be used to change the timing
of the sleep / wake cycle
Li ht b d b d t t t
Li
g
ht
exposure
b
y
d
ay can
b
e use
dt
o
t
rea
t
some
sleep timing disorders as well as SAD
Light exposure by day can also help restore a
Light exposure by day can also help restore a
stable sleep / wake cycle to Alzheimer’s patients
But light exposure at night is associated with the
But
,
light exposure at night is associated with the
incidence and progression of breast cancer
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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ImplicationsImplications
•The lighting of buildings
has to consider both the
visual and non-visual
effects of light exposure
•Daylight is the form of
li
g
htin
g
tested b
y
evolution
gg y
•Awareness of the impacts
of light on human health
may lead to more attention
may lead to more attention
being paid to the
daylighting of buildings
ImplicationsImplications
•More research really is
needed on light and health
•Care should be taken to
avoid over-generalization
of specific results
•Applications should be
chosen with an awareness
of the risks
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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47

Author biography
Peter R. Boyce, Ph.D., FIES, FSLL
Professor Emeritus
School of Architecture
Rensselaer Polytechnic Institute, Troy, New York
Background:
1965: Ph.D., physics, Reading University
1966-1990: Research Officer, Electricity Council Research Centre, England. Conducted research on
visual fatigue, the influence of age on visual performance, visual problems associated with visual
display units, hue discrimination, safe lighting for emergency conditions, and security lighting.
1990–2004: Head of Human Factors at the Lighting Research Center, Rensselaer Polytechnic Institute
. Conducted research on visual performance, visual comfort, circadian effects, emergency lighting,
perceptions of safety, and lighting for driving. Directed lighting evaluations and product testing.
Contributed to teaching program for MS in Lighting.
2004 to date: Independent consultant
2008 Technical editor, Lighting Research and Technology
Current interests:
Road lighting, lighting for the elderly, light pollution, lighting quality and photobiology
Professional memberships:
Society of Light and Lighting, U.K. (CIBSE), The Ergonomics Society, Illuminating Engineering
Society of North America,
Awards:
CIBSE Leon Gaster Award (five times), for papers on lighting applications
CIBSE Walsh Weston medal (three times) for papers on lighting research
Elenbaas Award for work in illuminating engineering
CIBSE Silver Medal, 1989
Fellow, Illuminating Engineering Society of North America, 1996
IESNA Taylor Technical Talent Award (twice), for papers on lighting
IESNA Medal, 2003
Institution of Lighting Engineers Best Lighting Journal Article, 2005
SLL Lighting Award, 2007
Publications:
Two books, Human Factors in Lighting (2003) and Lighting for Driving (2009), many book chapters,
and more than ninety papers in refereed journals.
SHB2009 - 2nd International Conference on Sustainable Healthy Buildings; Seoul, Korea.
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