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Lighting for work: A review of visual and biological effects


Abstract and Figures

With the detection in 2002 of a novel photoreceptor cell in the eye, the biological effects that light has can be better understood. From the research on the biological effects of lighting, it is evident that the rules governing the design of good and healthy lighting installations are, to a certain degree, different from the conventionally held rules. We demonstrate that it can be beneficial to be able to adapt both the level and the colour of the lighting. Not only the light on the visual task, but also that entering the eye determines the overall quality of lighting. In a working environment, not only are the advantages in terms of health and wellbeing important for the workers themselves, they also lead to better work performance, fewer errors, better safety, and lower absenteeism.
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Lighting for work:
visual and biological effects
Ir.W.J.M. van Bommel
Ir. G.J. van den Beld
April 2004
Philips Lighting, The Netherlands
Ir.W. J. M. van Bommel and Ir. G. J. van den Beld
The two authors, the former with a university degree in physics and the latter with a degree in electrical
engineering, joined Philips Lighting in the early 1970’s. They have since been involved in fundamental
lighting application research in many different application areas whilst occupying a number of different
positions within the company. They also actively participate in the work of the International
Commission on Illumination (CIE) and of the European Standardisation Technical Committee for
Light and Lighting (CEN TC 169), and have individually presented papers at many different national
and international Congresses. Their papers have also been published in many renowned lighting
Wout van Bommel has recently been elected president of CIE for the period 2003-2007.
Gerrit van den Beld is the Dutch representative of CIE Division 6: “Photobiology and Photochemistry”
and is a member of the Board of the Dutch Foundation: “Lighting and Health” that promotes a wider
medical-scientific knowledge of the influence of light on human beings.
“Lighting for Work: visual and biological effects” (April 2004) updates and extends the previous article
“Industrial lighting and productivity” by the same authors (August 2002) with the latest findings on the
biological effects of lighting on health and well being. For detailed information on lighting and industrial
productivity, please refer to pages 6 to 8 of the August 2002 article.
Three types of photoreceptor cells in the eye
Lighting and visual effects
Visual performance
Visual environment
Vision-related quality aspects of lighting installations
Lighting and biological effects
Light and body rhythms
Lighting, alertness, mood, and stress
Health-related quality aspects of lighting installations
Lighting for work:
visual and biological effects
With the detection in 2002 of a novel photoreceptor cell in the eye, the biological effects that light
has on human beings can be better understood. The spectral sensitivity of the novel cell type has in
the meantime been studied and shows that bluish light has biologically a larger activating effect
than does reddish light.
A large number of research projects that compare the effects on health, well-being and alertness as a
result of people working under different lighting conditions have been carried out. The results, as
summarised in this article, show that good lighting indeed has important beneficial effects, not
only visually but also biologically. From the research on the biological effects of lighting, it is
evident that the rules governing the design of good and healthy lighting installations are, to a
certain degree, different from the conventionally held rules. We demonstrate that it can be
beneficial to be able to adapt both the level and the colour of the lighting. Not only the light on the
visual task, but also that entering the eye determines the overall quality of lighting.
In a working environment, not only are the advantages in terms of health and well-being important
for the workers themselves, they also lead to better work performance, fewer errors, better safety,
and lower absenteeism. An example from an industrial environment demonstrates that by
changing the lighting from 300 to 500 lux may easily increase the overall productivity by 8 per
The visual effects of lighting have been studied for more than 500 years. Leonardo da Vinci (1452-1519)
described ideas about “street lighting”. Christiaan Huygens (1629–1695) formulated the wave theory of
light, while Sir Isaac Newton (1642-1727) developed the corpuscular theory of light. Johann Wolfgang
Goethe (1749-1832) analysed the colour effects and aspects of lighting.
With the introduction of gaslight and electric light in the early-to-mid 1800s, the study of visual lighting
effects was directed more and more towards practical lighting application research.
As regards the mechanism of visual effects, as early as 1722 the Dutchman Antony van Leeuwenhoek noted
the presence of “rod and cone cells” in the retina. Their existence was confirmed as “the light sensitive
photoreceptors” in 1834 by the German Gottfried Treviranus. This discovery opened the way to the
understanding of many of the visual lighting effects already described and to a more concrete investigation
into the visual effects of lighting, the goal being to design more effective lighting installations.
For more than 150 years, scientists considered rods and cones to be the only photoreceptor cells in the eye.
Seen in this historic context, it is sensational that in 2002 David Berson et al. [1] of the Brown University
(USA) detected a novel, third type of photoreceptor in the retina of mammals. This novel photoreceptor is a
“missing link” in describing the mechanism of biological effects as controlled by light and darkness. That
lighting has important biological effects has been the subject of extensive studies in the biological and
medical scientific world during the past twenty-five years. From this, we have learned that the effects of
good lighting extend much further than visual effects only: the biological effects mean that good lighting
has a positive influence on health, well-being, alertness, and even on sleep quality [2], [3], [4], [5]. At the
same time, it means that the lighting parameters with which good lighting can be described need to be
This article first describes the mechanism of both visual and biological effects based on the three
photoreceptors in the eye. Subsequent sections deal with lighting and visual effects, and lighting and
biological effects. The first of these sections concludes with a summary of the “vision-related” lighting
quality aspects, while the second concludes with a discussion of “health-related” lighting quality aspects.
Lighting for work: visual and biological effects
The photoreceptor cells in the retina of the eye, the cones and rods, regulate the visual effects. When light
reaches these cells, a complex chemical reaction occurs. The chemical that is formed (activated rhodopsin)
creates electrical impulses in the nerve that connects the photoreceptor cells with the back of the brain
(visual cortex). In the visual cortex of the brain the electrical impulses are interpreted as “vision”.
Figure 1 shows the nerve connection between cones and rods in the eye and the visual cortex of the brain.
The rods operate in extremely low-level light situations (scotopic vision) and do not permit colour vision.
The cone system is responsible for sharpness and detail and colour vision. For all indoor lighting situations,
the cones are to a very large extent decisive.
The sensitivity of the cone and rod systems varies with varying wavelength of light, and thus with varying
colour of light. This is illustrated in Figure 2, where the spectral eye sensitivity curves Vλfor the cone system
and V’λfor the rod system are given. The Vλcurve for the cone system is the basis for all lighting units such
as lumen, lux and candela. It is called the photopic system. As can be seen from the Vλcurve, the eye is not
very sensitive to extreme blue and extreme red light, and has its maximum sensitivity for green-yellow light.
Fig.1 Visual and biological
pathways in the brain:nerve
connections between the
retina of the eye,with its cones
and rods,and the visual cortex
on the one hand (in red) and
between the retina,with the
novel photoreceptor cell,and
the suprachiasmatic nucleus
(SNC) and the pineal gland
(in blue).
Fig.2 Spectral eye sensitivity
curves,Vλfor the cone system
(photopic vision:solid line) and
V’λfor the rod system
(dotted line).
pineal gland
% 75
400 500 600 700 800 nm
It should be noted that different light colours can be obtained by different mixtures of wavelengths.
White light consists of such a mixture. It is evident that the (visual) efficacy of a light source is very much
determined by the spectral eye sensitivity and the wavelengths that are incorporated in its light.
The novel photoreceptor cell type in the retina of the eye detected by David Berson et al. [1] in 2002
regulates the biological effects1. When light reaches these cells, a complex chemical reaction occurs (here
involving the photo pigment melanopsin [6]), again producing electrical impulses. These cells have their
“own” nerve connections to, amongst others, locations in the brain called the suprachiasmatic nucleus
(SNC), which is the biological clock of the brain, and the pineal gland. Figure 1 shows the nerve
connection between the novel photoreceptor cells in the eye and these locations in the brain.
The sensitivity of this novel photoreceptor cell also varies for different wavelengths of light, and thus for
different colours of light. On the basis of the biological factor “melatonin suppression”, Brainard [7] was
already able to determine the spectral “biological action” curve2. This curve is given in Figure 3, together
with the visual eye sensitivity curve of cones.
Lighting for work: visual and biological effects
Fig.3 Spectral biological action
curve (based on melatonin
suppression),in blue,
(source:Brainard [7]),
and the visual eye sensitivity
curve, in red.
By comparing the two curves it is immediately evident that the biological sensitivity for different
wavelengths of light is quite different from the visual sensitivity. Where the maximum visual sensitivity lies
in the yellow-green wavelength region, the maximum biological sensitivity lies in the blue region of the
spectrum. These phenomena have an important meaning for the specification of healthy lighting.
1Probably,the rods and cones do play a certain role in this respect as well.
2As will be discussed further on in this article, one of the biological effects of light is the suppression of the hormone melatonin.Probably many other biological factors regulated
by lighting will have an action spectrum similar to that determined on the basis of melatonin suppression.
% 75
400 500 600 700 800 nm
Visual performance
Lighting for work covers a wide range of different working interiors and tasks: from offices and small
workshops to huge factory halls, and from reading, writing and PC working tasks to fine precision work or
heavy industrial tasks.
The lighting quality should always be high enough to guarantee sufficient visual performance for the tasks
concerned. However, a person’s actual visual performance depends upon not only the quality of the lighting
but also upon his or her own “seeing abilities”. In this respect, age is an important criterion, since lighting
requirements increase with age. Figure 4 gives the relative amount of light required for reading a well-
printed book, as a function of age. This research was carried out with test persons wearing, if required, the
correct reading glasses. It is evident from this curve that the age effect is extremely severe. One of the many
reasons for this age effect is the deterioration of the transmittance of the eyes’ lenses: the lenses gradually
turn yellowish (see Figure 5). This deterioration means that the ageing lens has a lower transmittance.
It also means that less and less bluish light is transmitted. The ageing eye sees a less-blue world.
Fig.4 Relation between age and
relative amount of light required
for reading good print
(source:Fortuin [8]).
Fig.5 Lens transmittance for
various age categories.Values
are expressed as a percentage
of the 560 nm point for the new
born (source:adapted from
Brainard et al.[9]).
300 350 400 450 500 550 600
wavelength (nm)
% transmittance
new born
20-29 years
60-69 years
0 10203040506070
age (years)
ight requirement
Figure 6 serves as an illustration of the many research results pertaining to the influence of lighting quality
on visual performance. It gives the relative visual performance as a function of lighting level for different
visual task difficulties: one for a moderately difficult task (e.g. office work or general machine work in an
industrial environment) and another for a difficult task (e.g. colour inspection work or fine assembly work).
All tasks show a clear increase in visual performance with increased lighting quality – in this example the
lighting level. In the graph, the required lighting levels (EN) for industrial environments, as in many cases
specified in the European Norm for the lighting of work places [10], are indicated.
Lighting for work: visual and biological effects
The graph shows that the requirements laid down in the European Norm are, in fact, well-suited to the
younger persons. However, the visual performance of the older workers is considerably lower. Luckily,
compensation with a higher lighting level is completely possible for the moderately difficult task. In
practice, this calls for adaptable lighting on top of the lighting required by the “EN Standard” for those
moments that daylight is not sufficient to give the higher lighting levels needed for the older workers.
Of course, an improvement in visual performance yields, in its turn, an improvement in sustained work
performance, reflected in a higher output and in a lower number of errors. The extent to which good-
quality lighting enhances work performance depends on the visual component of the task. A task with an
important visual component will benefit more from good seeing conditions than a task with a less
important visual component.
Visual environment
Besides its effect on visual performance, lighting can also have a powerful influence on atmosphere and the
visual impression of the workplace. Properly designed, the overall working environment can have a
stimulating effect on the people working within it [12]. Today, a lot of emphasis is placed on the layout and
interior design of the workplace. Good lighting can strengthen the interior design, but poorly-designed
lighting can diminish or even “destroy” the effect of the interior design.
One aspect that is important in this respect is a controlled brightness of the surfaces that form the physical
limits of the space, such as walls, floor and ceiling. The brightness of these surfaces determine to a large
extent how the total space is experienced. Another factor is a proper limitation of glare and undesirable light
reflections. Glare is the sensation produced by brightness levels within the visual field that are considerably
greater than the brightness to which the eyes are adapted. Owing to limitations in the adaptation properties
of the eye, abrupt changes in brightness may lead to reduced visual performance and to visual stress and
Fig.6 Relation between
relative visual performance
(in %) and lighting level (in lux).
Continuous blue line:young
persons;broken red line: older
persons (source:CIE [11]).
EN:lighting levels specified in
the European Norm.
100 300 500 1000 3000
level (lux)
visual performance (%)
100 300 500 1000 3000
visual performance (%)
difficult task
Difficult task
The colour properties of the light should also receive considerable attention. The lighting should permit the
“real” colours to be seen. Proper colour rendering of the human skin is especially important, since lighting
that makes the skin look pale and unhealthy often leads to complaints. Also, the colour appearance of the
light itself plays a role in providing the space with an atmosphere. It may even have an emotional influence.
For example, a somewhat bluish-white light gives a cool impression that is often experienced as
businesslike, while reddish-white light gives a warm impression that may be experienced as cosy and
Finally, daylight contribution to the interior is another very important factor determining the quality of the
working environment. Fortunately, in many cases daylight penetrates the building for at least several hours
each day, considerably increasing the overall lighting levels. But daylight not only facilitates the visual
performance of the visual task by contributing to the lighting on that task; because of its dynamic, varying
character in both intensity and colour, it also contributes greatly, if properly controlled (e.g. by proper
window and sun-shielding design), to a good working environment. The dynamic changes in daylight have
a positive influence on mood and stimulation. An extensive study under office conditions has shown that
people prefer artificial lighting in addition to the normal daylighting present in an office environment:
average 800 lux on top of the prevailing daylight contribution [13].
Vision-related quality aspects of lighting installations
Most national and international recommendations and standards specify lighting quality figures for the
majority of the visual quality aspects mentioned above, and for a wide variety of interiors and activities.
Table 1 lists the visual quality aspects together with the most important parameter for each aspect as used in
the European Norm for the lighting of workplaces.
It should be noted that the colour appearance of the light itself is not specified in the European Norm.
The reason for this is that so far the colour appearance is seen as a matter of psychology and aesthetics and
is considered to be natural.
Table 1 Visual quality aspects
of lighting installations with
their quality parameters as
specified in the European
Norm for the lighting of
workplaces [10].
Visual quality aspect Quality parameter
Lighting level Average illuminance level,Eav
Spatial distribution Uniformity:Emin / Eav
Glare restriction:UGR
Colour rendering Ra
As an illustration of what quality is required in different situations, Tables 2 and 3 give the required values
specified in the European Norm for an office and for an industrial environment (the chemical, plastics and
rubber industries)3. These requirements are values that meet the needs of visual performance and visual
comfort for workplaces for the majority of the workforce. However, as discussed above, the age effect is so
important that adaptable lighting on top of the “EN Standard lighting” is needed for those moments when
daylight is not sufficient to give the higher lighting levels that are required for the ageing eye.
3 Offices Type of interior,task or activity ¯
Em UGRL Ra Remarks
3.1 Filing,copying, etc. 300 19 80
3.2 Writing,typing,reading, 500 19 80 DSE-work:
data processing see clause 4.11.
3.3 Technical drawing 750 16 80
3.4 CAD workstations 500 19 80 DSE-work:
see clause 4.11.
3.5 Conference and meeting rooms 500 19 80 Lighting should be
3.6 Reception desk 300 22 80
3.7 Archives 200 25 80
2.5 Chemical,plastics and rubber industry Type of interior,task or activity ¯
Em UGRL Ra Remarks
2.5.1 Remotely-operated processing 50 - 20 Safety colours
installations shall be recognisable
2.5.2 Processing installations with limited 150 28 40
manual intervention
2.5.3 Constantly-manned workplaces 300 25 80
in processing installations
2.5.4 Precision measuring rooms,laboratories 500 19 80
2.5.5 Pharmaceutical production 500 22 80
2.5.6 Tyre production 500 22 80
2.5.7 Colour inspection 1000 16 90 TCP 4000 K.
2.5.8 Cutting,finishing,inspection 750 19 80
Lighting for work: visual and biological effects
Table 2 Lighting requirements
for offices
(source:EN 12 464 [10]).
Table 3 Lighting requirements
for the chemical,plastics and
rubber industries
(source:EN 12 464 [10]).
3The values specified for the average illuminance are “maintained illuminances”:viz. values below which the average illuminance on the specified surface is never allowed to fall.
The value specified for uniformity on the task is always the same:Emin / Eav 0.7.
Fig.7 Double plot
(2 x 24 hours.) of typical daily
rhythms of body temperature,
melatonin,cor tisol,and
alertness in humans for a
natural 24-hour light/dark
The beneficial effect of (day)light has been well known since ancient times, an example being heliotherapy,
or the treatment of disease by exposure of the body to the suns rays. Light therapy for dealing with health
problems was popular until the 1930s, after which time the introduction of penicillin led to
pharmaceuticals taking the leading role. Over the last 20 to 30 years, however, the appreciation of light as
an important contributor to health and well-being has been revived, thanks to various findings in biological
and medical research.
We normally think of the eye as an organ for vision, but due to the discovery of additional nerve
connections from recently-detected novel photoreceptor cells in the eye to the brain, it is now understood
how light also mediates and controls a large number of biochemical processes in the human body.
The most important findings are related to the control of the biological clock and to the regulation of some
important hormones through regular light-dark rhythms. This in turn means that lighting has a large
influence on health, well-being and alertness.
Light and body rhythms
Light sends signals via the novel photoreceptor cells and a separate nerve system to our biological clock,
which in turn regulates the circadian (daily) and circannual (seasonal) rhythms of a large variety of bodily
processes. Figure 7 illustrates some typical rhythms in human beings. The figure shows only a few examples:
body temperature, alertness, and the hormones cortisol and melatonin
6 121824 121824 66
body temp.
The hormones cortisol (“stress hormone”) and melatonin (“sleep hormone”) play an important role in
governing alertness and sleep. Cortisol, amongst others, increases blood sugar to give the body energy and
enhances the immune system. However, when cortisol levels are too high over an extended period, the
system becomes exhausted and inefficient. Cortisol levels increase in the morning and prepare the body for
the coming day’s activity. They remain at a sufficiently high level over the course of the bright day, falling
finally to a minimum at midnight. The level of the sleep hormone melatonin drops in the morning,
reducing sleepiness. It normally rises again when it becomes dark, permitting healthy sleep (also because
cortisol is then at its minimum level). For good health, it is of importance that these rhythms are not
disrupted too much. In case of a disruption of the rhythm, bright light in the morning helps restoring the
normal rhythm.
Lighting for work: visual and biological effects
In a natural setting, light, especially morning light, synchronises the internal body clock to the earth’s 24-
hour light-dark rotational cycle. Without the regular 24-hour light-dark cycle, the internal clock would be
free-running with, for humans, an average period of about 24 hours and 15 to 30 minutes. This would, as a
consequence, produce ever-greater day-to-day deviations in our body temperature, cortisol and melatonin
levels from those set by the environmental clock time [14]. This deharmonisation in the absence of the
“normal” light-dark rhythm would result in an incorrect rhythm of alertness and sleepiness, ultimately
leading to alertness during the dark hours and sleepiness during the bright hours. In fact, the same
symptoms, and for the same reasons are associated with jet lag after travelling over several time zones [15].
Rotating shift workers also experience the same symptoms for a couple of days after each shift change, again
for the same reason [16].
Lighting, alertness, mood,and stress
A wealth of research projects that compare the effects of health, well-being and alertness as a result of people
working under different lighting conditions have already been carried out. In this article we will discuss
only a limited but typical number of these.
Küller and Wetterberg [17] studied the brain-wave pattern (EEG) of people in a laboratory made to look
like an office environment, once with a relatively high lighting level (1700 lux) and once with a relatively
low lighting level (450 lux). The composition of the EEGs exhibit a pronounced difference: the higher
lighting level results in fewer delta waves (the delta activity of an EEG being an indicator of sleepiness),
meaning that bright light has an alerting influence on the central nervous system (see Figure 8).
Many investigations into the effects of light on alertness and mood have been carried out under night-shift
conditions, because here the effects to be expected would be strongest. Figure 9 shows the effect of two
lighting regimes on arousal as a function of time at work for shift-workers [15]. A decline in arousal over the
night occurs for both regimes, but the high-light regime always results in a significantly increased arousal
level and thus better alertness and mood.
1700 450
left hemisphere
of brain
right hemisphere
of brain
EEG delta activity (%)
024 68
time (hrs. after midnight)
arousal level
Fig.8 Delta activity in the EEG
of office workers under lighting
levels of 450 lux and 1700 lux
(source:Küller and Wetterberg
Fig.9 Alertness and mood
expressed as arousal level for
lighting levels of 250 lux and
2800 lux,as a function of
working hours after midnight
(source:Boyce et al. [18]).
Other studies show that the use of higher lighting levels to cope with fatigue results in the subjects indeed
staying alert longer [19], [20], [21].
Studies of stress levels and complaints in people working indoors have been made by comparing a group of
people working solely under artificial light with a group working under a combination of artificial light and
daylight [22]. As can be seen from Figure 10, in January, when daylight penetration is not sufficient to
make a substantial contribution to the lighting level, there is hardly any difference between the two groups.
But in May, when daylight really contributes, the group benefiting from daylight has a considerably lower
stress complaint level. Another study shows that bright artificial light in interiors in winter has a positive
effect on mood and vitality [23].
Fig.10 Stress complaint levels
(with statistical spread) in a
group of workers working
either under artificial light only
or under a combination of
artificial and daylight
(source:Kerkhof [23]).
Some, but few people experience headaches because of the light ripple caused by the 50 Hz power supply of
fluorescent lamps operated on magnetic ballasts. Fluorescent lamps running on modern, high-frequency
electronic ballasts operate at around 30 kHz and thus do not exhibit this flicker or ripple phenomenon. In a
comparison, it has been found that the occurrence of headache is, indeed, significantly lower when
electronic ballasts are used [24]. Küller and Laike [25] measured the EEG of persons working in an office
environment under respectively magnetic (50 Hz) and high-frequency fluorescent lighting. At the same
time, they also measured the speed and errors made in a proof-reading task. Figure 11 shows that the
reciprocal value of the alpha activity of the EEG, and therefore the brain arousal (“stress”), is higher with the
50 Hz operated lighting. The working speed is slightly higher, but the errors are dramatically higher (more
than double). The combined effect means that it is wise, from both the well-being and productivity points
of view, to use high-frequency fluorescent lighting instead of magnetic 50 Hz lighting to limit brain arousal
or stress.
Fig.11 Brain arousal measured
as the reciprocal value of the
alpha activity of EEGs in
persons in offices under 50 Hz
and under high-frequency HF
(30 kHz) fluorescent lighting.
The working speed and errors
of a proof-reading task are also
given (graph adapted from:
Küller and Laike [25]).Subject
group:high flicker sensitivity.
Stress Level
January May artificial light only
artificial light + daylight
HF 50 Hz HF 50 Hz HF 50 Hz
brain arousal speed errors
Lighting for work: visual and biological effects
Health-related quality aspects of lighting installations
The visual-quality aspects of lighting installations as listed in an earlier section, i.e. lighting level, spatial
distribution of light and colour rendering, have to be refined and extended if we want to arrive at truly
“good and healthy” lighting installations.
The biological effect of light is not steered directly by the illuminance on the working plane, but by light
entering the eye. Studies are under way to see how this difference between “visual lighting level on the task”
and “biological lighting levels” can be accounted for [26]4.
As has been illustrated, especially because of the effects due to ageing eyes, the lighting level has to be
Daylight by its nature is dynamic in its intensity. There are indications that a variable lighting condition has
a positive effect on the activation state of people in an office environment [28]. Where the benefits of the
dynamics of daylight intensity are not sufficiently available, dynamic artificial light can be advantageous.
Two complete new aspects relate to the timing and duration of the lighting. Visually, of course, light is only
needed when and for as long as one “views”. Biologically, however, the time when the light (or darkness) is
received and its duration plays an essential role, as is evident from the rhythm graph of Figure 7.
We have always realised that the colour of light itself has an emotional meaning, and is therefore important
for the atmosphere of a space. But we now also understand that the spectrum and thus the colour of light
has an important biological meaning. As was shown in the section on the novel photoreceptor cell, bluish,
cool light has biologically a larger effect than warmer coloured reddish light (Figure 3). The daylight
situations of the photographs shown in Figure 12 produce not only a different emotional feeling but also
have a different biological effect.
Fig.12 Ambient colour early in
the morning and early in the
evening in Paris.
4Very recent research indicates that light on the upper and lower part of the retina has different importance as far as the resulting biological effect is concerned [27].This suggests
that also the spatial distribution of light is important from a “health” point of view.
The bluish morning light has biologically an activating (alerting) effect, while the red sky in the early
evening has a relaxing effect. In a working environment, both activating and relaxing moments are
required. The colour and lighting level of the artificial lighting together may help to create these moments.
Studies on the preferred colour of light in an office environment have shown that there is no trend in
preference between individuals in this respect: everyone has their own personal preference (Figure 13).
Fig.13 Colour preference of
artificial light in an office with
(daylight) windows,expressed
as correlated colour
temperature of the light Tk for
different ages and for men and
women (source:Tenner [29]).
Table 4 Vision- and health-
related quality aspects of
lighting installations
Table 4 summarises the vision- (from Table 1) and health-related lighting quality aspects that together
determine “good and healthy” lighting.
Lighting quality aspects
Vision related Health related
(adaptable) lighting level on the task (adaptable) lighting level in the eye
spatial distribution spatial distribution
colour rendering (adaptable) colour appearance
20 30 40 50 60
Lighting for work: visual and biological effects
Thanks to the recent discovery of a novel photoreceptor in the eye, we are now much better able to
understand why the benefits of good lighting at work, taking into account both the visual effects and the
biological effects (viz. health, well-being and alertness), are so important. Apart from the health and well-
being advantages for the workers themselves, good lighting also leads to better work performance (speed),
fewer errors and rejects, better safety, fewer accidents, and lower absenteeism. The overall effect of all this is
better productivity.
For an industrial environment (moderately difficult visual task), we investigated the possible resulting total
productivity increase as a result of improved lighting level [30]. Table 5 provides a summary of the results.
Improvement of lighting level Productivity increase
From 300 to 500 lux 8 %
From 300 to 2000 lux 20 %
To confirm the results, we are carrying out real-life productivity investigations in a number of industrial
environments where the lighting has recently been renovated. Realising the importance of the biological
component in the productivity increase, we believe that similar figures can also be obtained in an office
By putting our advice for flexible and adaptable lighting levels and colours into practice, such productivity
advantages will become even more impressive.
[1] Berson, D.M., Dunn, F.A., Motoharu Takao; “Phototransduction by retinal ganglion cells that set the
circadion clock”, Science, February 8; (2002).
[2] van den Beld, G.J., “Licht und Gesundheit”, Licht 2002 Tagung, Maastricht, (2002).
[3] van den Beld, G.J., “Healthy lighting, recommendations for workers”, Symposium healthy lighting at
work and at home, University of Technology Eindhoven, (2002).
[4] Veith, J.A., “Principles of healthy lighting: highlights of CIE TC 6-11’s forthcoming report”, Fifth
International LRO lighting research symposium, Orlando, (2002).
[5] NSVV Recommendation: “Light and Health in the workplace”, ISBN 90-76549-21-4, Haarlem
[6] Berson, D.M.; “Melanopsin and phototransduction by retinal ganglion cells”, Fifth International
LRO lighting research symposium, Orlando, (2002).
[7] Brainard, G.C., “Photoreception for regulation of melatonin and the circadian system in humans”,
Fifth International LRO lighting research symposium, Orlando, (2002).
[8] Fortuin, G. J., “Visual power and visibility”, Philips Research Report 6, (1951).
[9] Brainard, G.C. et al. “Action spectrum for melatonin regulation in humans: Evidence for a novel
circadian photoreceptor”, Journal of Neuroscience (2001).
Table 5 Increase in
productivity in the metal-
working industry with a
moderately difficult visual task
as the combined effect of
increased work performance,
errors/ rejects reduction and
accident reduction (source:
van Bommel et al.[30]).
[10] European Standard EN 12464, “Lighting of workplaces”, (Comité Européen de Normalisation,
CEN), (2003).
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... Good lighting is required for good visibility of the environment and should provide a luminous environment that is human-friendly and appropriate for the visual task performed. Various studies have been conducted in order to identify the effects of lighting towards human health, productivity, and well-being and alertness level (Boyce et al., 2003;Hameed & Amjad, 2009;van Bommel & van den Beld, 2004).In regards of human perception, two of the most important characteristics of lights are illumination and correlated colour temperature (CCT) (Barkmann et al., 2012;Veitch & Newsham, 1998a).Recently, studies have proven that different CCT provided by different lighting are important in affecting human beings psychologically and physiologically, through their visual and non-visual processes(IEA, 2010). CCT is found to have effects on visual and mental fatigue. ...
... This implies that the better quality of office space is essential for every occupant in the office. which, along with modular workstations, provide a flexible, open-plan environment that enhances communication and collaboration among employees while making future moves and changes easier (Troukens, 2001). Demountable partitions placed in the office are blocking the window from space to space and become an encumbrance to allow daylight to enter, the space will become gloomy. ...
... In the year 2002, David Berson noted that apart from traditional photoreceptors (rods and cones) typically responsible for vision, in mammals' retina, there is another photoreceptor called intrinsically photosensitive retinal ganglion (ipRGC) (Pauley, 2004). This is a part of the suprachiasmatic nuclear (SCN) of the hypothalamus (van Bommel & van den Beld, 2004) which is a section of the brain that controls the body circadian cycle and is mostly involved in several nonimage forming functions such as promoting alertness, mood, cognitive performance, controlling body metabolism, DNA damage response, hormone production, and even cell cycle regulation and division (Kruisselbrink et al., 2018;Stevens et al., 2013). ...
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Workspace is a place should be concerned by society since that people spend one third of their life in it. The quality of workplace can be based on visual comfort and occupants’ job satisfaction. Job satisfaction can affect not only occupants’ performance during work and affects occupants physically and psychologically. Visual comfort is one of the factors can affect job satisfaction of office occupants. Poor visual comfort can cause eyestrain, eye fatigue and even affects occupants’ circadian rhythms. This can affect occupants’ moods and well-being. Visual comfort can be achieved by natural lighting and artificial lighting. This paper will just mention about artificial lighting. Artificial lighting plays a key role in creating a healthy environment that enhance visual comfort in office and increase productivity of office occupants since that natural lighting is not under control due to weather. This study aims to provide a better quality of working environment in shop office by applying appropriate artificial lighting and the effects on employees’ performance during work. Objective of this study is to identify the factors that affect employees’ performance based on visual sector. Investigate the job satisfaction of employees with their working environment and find out the effects of different level of illuminance and correlated colour temperature (CCT).
... Findings from the areas of medicine, biology and psychology confirm this and report benefits on vision improvement and eyestrain reduction, as well as on non-visual effects (Aries et al., 2013;Silvester and Konstantinou, 2010;Boubekri, 2004;Edwards and Torcellini, 2002). While the study of light's visual effects date back to the fifteenth century, the study of non-visual effects has taken place only in the last four decades (Van Bommel and Van den Beld, 2004). The vital role of eye and skin exposure to sunlight in the process of Vitamin D production and rickets has been established (Glerup et al., 2000;Liberman, 1991) and further work is examining subsequent effects on bone frailty, blood pressure changes, mood, depression and a range of seasonal affective conditions (Shishegar and Boubekri, 2016). ...
... Recent research has indicated that green landscapes improve the rate of student recovery from stressful experiences (Li and Sullivan, 2016). Moreover, in terms of mood and stimulation, these are positively influenced by the dynamic nature of daylight and the variable light conditions it creates (Van Bommel and Van den Beld, 2004). ...
Research confirms that daylight is important not only for vision, but also for general well-being. Little is known, however, about how real world occupied spaces perform in terms of daylight. This holds true particularly in schools, where practicalities prevent the collection of data from classrooms in use. The framework presented here addresses the lack of daylighting performance evidence from the real world, necessary for guiding daylighting predictions for classroom design. It describes and prototypes a methodology that achieves long-term daylighting performance monitoring in classrooms in use. This methodology also enables the observation of actions the occupants take to sustain or improve their visual comfort. Four UK secondary school classrooms were used as case studies and were monitored for up to a year. A mixed method approach was taken in order to associate measured luminance, a physical characteristic of light, to user interaction with electric lights and blinds, as well as student subjective responses. This resulted in two novel fine-grained year-long datasets, as well as a record of student appraisals of the luminous environment. The luminance dataset contains over a trillion measurements captured on-site simultaneously for multiple (nearly 18,000,000) points in space, at a 10-minute frequency over a year, resulting in multiple (over 62,000) points in time. Application of the long-term monitoring method was found to be robust and useful for monitoring complex multi-user spaces for at least six consecutive months. Combining fine-grained luminance mapping, records of occupant interactions with design elements and occupant subjective views of the case study classrooms provided a better understanding of the many factors that shape operational daylighting performance. This was achieved by identifying specific parameters, examining their effect across a set of the three types of evidence and highlighting the complex relationships detected between them. The three aspect framework presented here contributes to a philosophy of research that addresses real world challenges by combining their technical, behavioural and subjective expressions. In doing so it supports the view that sustainable and thus effective solutions are those that stem from holistic people-centred interdisciplinary research.
... 495 Moreover, as discussed in section 3.4.4 regarding environmental noise exposure, 485 Cited in van Bommel & van den Beld (2004). 486 The authors reported the following outcomes among nurses who were working in the nursing stations with windows: 'communication (p < 0.0001) and laughter (p = 0.03) both increased, and the subsidiary behaviour indicators of sleepiness and deteriorated mood (p = 0.02) decreased. ...
... See: Boubekri et al. (2014). 557 van Bommel & van den Beld (2004), cited in Mujan et al. (2019). 558 Boyce et al. (2003). ...
Technical Report
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There is strong evidence that a poor indoor climate has a significant impact on people's health and well-being, and that in turn has wider socio-economic consequences, such as via its impact on work attendance, productivity and performance. Four indoor hazards in particular were identified and used in the analysis: Damp and mould; Noise pollution; Indoor temperature (excess cold), and; Lack of daylight. The objective of this study was to undertake a detailed analysis of the impact of the indoor climate across all age groups in the EU and the UK, Norway and Switzerland.
... Regarding emotions, light colour and intensity have been found to impact on productivity, mood and room perception [40,41], with daylight showing a positive impact due to its dynamic nature positively influencing mood and arousal [42,43]. Occupants seem however to prefer the completion of daylight input with artificial lighting [44]. ...
Electric lighting energy expenses has gained importance in the last decades representing a large part of the global energy expense worldwide. The increase of the proportion of glazed building facades is an incomplete solution raising other problems regarding thermal and visual comfort, while rebound effects in terms of lighting usage lowered the energetic benefits of LED technology. Another strategy to address the issue of energy is the well-known strategy of the re-introduction of task lights. The current study presents a system arbitrating the contribution of daylight with general and task electric lighting from the prediction of key performance indicators (work plane illuminance and daylight glare probability) by a machine learning model. It aims at reducing energy consumption while minimizing the impact on occupants’ comfort and productivity. This system was validated by the mean of a controlled user experiment with 60 participants. Altogether, our data revealed that RADIANCE simulations model accurately predicts on-site monitoring (R2=.96) and that the machine learning model accurately predicts RADIANCE simulations for both work plane illuminance (R2=.99) and daylight glare probability (R2=.99) allowing to operate the automated system. Data from the user experiment shows that our system successfully saves 35 Wh on average compared to manual operation of the room by users, by making prior use of daylight and task lighting. This represents more than halving the energy demand. Importantly, the automation impacted neither users’ comfort or task performance. System acceptance constructs such as system reliability or trust in the system were found to be linked with an attribution of the locus of control to powerful others. This result suggests that the key towards high user acceptance might lie in purposefully addressing this dimension. Altogether, the presented results support the potential for energy saving through the development of user-centred lighting automation.
... We would like to highlight other valuable literature reviews that have addressed the effects of indoor lighting on task performance [106], examined the evidence on lighting for work beyond visual responses [17,[107][108][109], the effects of windows in the work environment [110], occupants' preferences towards daylighting and control systems [111] and how occupant's behavior can contribute to energy savings [112]. ...
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This paper presents a critical review of studies addressing the effects of window views, daylighting, and lighting on occupant behavior, perception, performance, and well-being. A systematic search in the Scopus database was performed in November 2021 and yielded 515 hits. Seventy-six studies were selected according to the following criteria: i) papers presenting research results with participants' responses and ii) accounting for daylighting, lighting, or window view assessments. The study and setting features, participants, predictors and outcomes, the statistical approach, the reported significance level, and study limitations were extracted from each paper. The analysis then identified differences in the effect of the predictor on the outcome. The number of records obtained through the structured analysis was 240. A wide range of predictors have been used in indoor daylighting, lighting, and window view research to assess people's responses. The most commonly used predictors were artificial lighting features and window features -qualitative predictors - followed by some properties of the light sources, such as correlated color temperature, spectral distribution and horizontal illuminance. Differences in the methods for data collection, the used predictors, the outcomes, and the ways to measure the outcomes generated inconclusive results or results that were limited to the specific study. We extracted data from selected studies to suggest a simple model for the prediction of occupant performance from illuminance and correlated color temperature. The data points were few and scattered and the model, therefore, suffers from considerable uncertainties. Yet, it quantifies performance effects in ranges that are comparable with similar models from other indoor environment domains.
... Researchers (Bommel and Beld, 2004;Nagy et al., 1995) reported that natural lighting from doors, windows and any other opening in the building poses more importance to the occupants' comfort more than its primary requirement for view and light, it also has an impact on occupants' psychological needs. Non-natural lighting is an alternative vital lighting mode in a building. ...
Conference Paper
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The COVID 19 pandemic has caused a dramatic change in the human lifestyle. This change has had devastating effects on human health and productivity. Currently, people spend a substantial amount of time indoor due to the lockdown of the pandemic. Consequently, the impact of indoor environmental quality (IEQ) on building occupants’ health and productivity becomes a crucial area of study which needs urgent attention. Therefore, this paper discusses the critical factors affecting IEQ in buildings and their impacts on occupants. The methodology involves a thorough review and analysis of selected published journals. The search included journal articles, books, and conference proceedings on the impact of IEQ on building occupants from different databases, including ScienceDirect, Taylor, and Francis, among others. Five (5) critical factors influencing IEQ were identified from the 70 reviewed literature. These factors are ‘building plan layout, indoor air quality, indoor thermal condition, indoor lighting quality, and acoustic environment comfort’. The impacts of the identified factors on residential occupants’ productivity and health were discussed. The current change in the lifestyle in which most activities are done indoors calls for a reexamination of the factors that impact building occupants’ health and productivity. This paper provides an understanding of the critical factors affecting building occupants' productivity and general lifestyle. The knowledge of these vital factors will not only assist the construction professionals in their decision-making. Still, it will promote new construction innovations that can improve building occupants' health and productivity.
... Studies have shown that both natural and artificial lighting affects people's health, mood, and alertness (Cajochen 2007;Van Bommel, et al 2004). For this reason, it can be said that the lighting systems of educational buildings directly affect the academic performance of students (Sleegers et al, 2013). ...
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Educational buildings need to be properly built and renovated because of the number of users served, the rate of usage, the potential for energy savings, and their number in public buildings. Physically, educational buildings that do not meet the essentialcomfort conditions cause more energy consumption, have a negative effect on academic performance of students and also cause disruptions in educational program applications. According to 2021 data, there are approximately 67,000 school buildings in Turkey.A major portion of these buildings were constructed before 2000 and are now nearing the end of their economic life. It is essential to renew the insufficient buildings make them suitable for the conditions of the age. In this context, resilient systems that continue to function in a variety of negative conditions while maintaining comfort conditions become a priority in the design of the created environment. The lighting arrangements of educational buildings that are directly connected to visual comfort, academic performance, and energy consumption are discussed in this study. Within the framework of resilient design, certain suggestions have been developed in light of the current lighting standards in effect regarding the processes to be followed before the retrofit works to be performed in the lighting arrangements of the school buildings. These suggestions were discussed in three categories as short-, medium-, and long-termperiods, taking into consideration the duration of the improvement processes and without interfering with the existing activities during the school education period and it was aimed to create a guide for designers and practitioners with the improvement systematics to be made in these periods. In order to test these suggestions, a classroom from the Ministry of National Education's type school projects is used as an example. The existing situation of the natural and artificial lighting system of this classroom and short-, medium-and long-termimprovement suggestions were estimated through the Dialux Evo program. According to the findings, the recommended improvements enhanced visual comfort criteria and resulted in a considerable reduction in energy consumption. With the help of the improvement calendar, it is possible to modify the lighting systems of existing school buildings and increase visual performance. Keywords:school lighting design, retrofit, resilient lighting design, visual comfort, educational buildings
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Multiple environmental changes are related to mental disorders. However, research on the association between artificial light at night (ALAN) and mental health in China is limited, particularly at the national level. We used a “difference-in-differences” design and logistic regression to explore the relationship between ALAN changes and scores on self-assessed mental health. Participants were drawn from the China Family Panel Studies of adults in 2012 and 2018. The final analysis was based on 21,036 adults from 25 provinces throughout China. The brighter the ALAN, the worse was the mental health, and this connection was unaffected by particulate matter 2.5 (PM2.5) or temperature. ALAN sensitivity may differ among populations. Our findings suggest that exposure to brighter ALAN is associated significantly with worse mental health among Chinese adults. Environmental policies that reduce ALAN could improve the mental health of the Chinese public. Graphical abstract
The proper consideration of daylight in indoor environments refers to guaranteeing sufficient light levels while minimizing the risks of glare. Currently, The International Organization Standardization-ISO and the International Commission on Illumination-CIE establish that, for classrooms, the proper lighting level oscillates between 300–500 lx. Despite this, there is evidence of differences in the daylighting levels perceived as sufficient. The objective of this article is to identify and to explain the differences in perception of daylighting sufficiency to perform typical reading and writing activities in four cities in Colombia with latitudes that oscillate between 3°25’18”N to 6°15’7”N: Armenia, Cali, Medellin and Manizales. A methodology that included the application of surveys to university students in classrooms was outlined; at the same time workplane illuminance was measured in the workstations and vertical illuminance at the height of the eyes of people. The results showed differences between cities in the proportion of people who perceive certain daylighting level as sufficiently illuminated. A logistic regression model showed that those differences can be explained from the global solar radiation of each city.
Commercially available desk lamps are generally designed for reading books, and their traditional lighting designs are not suitable for working environments with computer monitors. However, the general public uses conventional desk lamps in their computer monitor working environment because they do not understand the difference, which may lead to eye fatigue and discomfort. In recent years, lights specially designed for a computer monitor working environment have appeared on the market to offer users more comfortable lighting. The objectives of this study are to define the main lighting elements via literature review and expert discussions, and to conduct experiments to investigate the design elements necessary to provide good lighting in a computer monitor working environment, thereby offering better lighting solutions in the future. This study organized the relevant industry guidelines and design principles, in which the BenQ Screenbar was used as the sample and different color temperature and illumination mode combinations were adopted as variables. A total of 22 subjects participated in the experiment. The goal was to investigate what lighting elements are required to optimize the computer monitor working environment, identify the most suitable lighting modes, and provide a reference for developing such products in the future.
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The weekly incidence of headaches among office workers was compared when the offices were lit by fluorescent lighting where the fluorescent tubes were operated by (a) a conventional switch-start circuit with choke ballast providing illumination that pulsated with a modulation depth of 43-49% and a principal frequency component at 100 Hz; (b) an electronic start circuit with choke ballast giving illumination with similar characteristics; (c) an electronic ballast driving the lamps at about 32 kHz and reducing the 100 Hz modulation to less than 7%. In a double-blind cross-over design, the average incidence of headaches and eyestrain was more than halved under high-frequency lighting. The incidence was unaffected by the speed with which the tubes ignited. Headaches tended to decrease with the height of the office above the ground and thus with increasing natural light. Office occupants chose to switch on the high-frequency lighting for 30% longer on average.
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This experiment was designed to establish whether lighting provided by a daylight-simulating skylight could be used to enhance the task performance and mood of night-shift workers. Subjects performed a series of cognitive tasks, gave subjective ratings of their mood and had their core temperature measured six times during each shift, for three successive nights, under the same lighting condition. Each shift ran from 00.00 hours to 07.59 hours. The subjects also kept a daily diary recording their general health, times of sleep and sleep quality for the complete period of the experiment. Four lighting conditions were experienced: a fixed low-illuminance condition; a fixed high-illuminance condition; an increasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from dawn to midday; and a decreasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from midday to dusk. There was a three day rest period before exposure to each lighting condition. The high, increasing and decreasing illuminance conditions produced higher core body temperatures and greater subjective arousal than did the low illuminance condition, on all three nights. The high- and decreasing-illuminance conditions improved the performance of complex cognitive tasks relative to the low and increasing illuminance conditions, on all three nights. There was no difference between the lighting conditions for the performance of simple cognitive tasks. The high illuminance condition led to a greater delay in going to bed following the shift than did the low-illuminance condition.
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Regulation of circadian period in humans was thought to differ from that of other species, with the period of the activity rhythm reported to range from 13 to 65 hours (median 25.2 hours) and the period of the body temperature rhythm reported to average 25 hours in adulthood, and to shorten with age. However, those observations were based on studies of humans exposed to light levels sufficient to confound circadian period estimation. Precise estimation of the periods of the endogenous circadian rhythms of melatonin, core body temperature, and cortisol in healthy young and older individuals living in carefully controlled lighting conditions has now revealed that the intrinsic period of the human circadian pacemaker averages 24.18 hours in both age groups, with a tight distribution consistent with other species. These findings have important implications for understanding the pathophysiology of disrupted sleep in older people.
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A century of research and practice have optimized the use of electric lighting in buildings to support human vision. However, recent lines of research show that light is also important to human circadian regulation, as reflected in such diverse phenomena as depression, sleep quality, alertness, and, perhaps, even health. Although light is essential to both vision and circadian regulation, research shows that the biophysical processes that govern circadian regulation are very different from those that govern vision. This growing body of research will probably influence the architectural lighting community and manufacturers to reoptimize the use of electric lighting in buildings to support both human vision and circadian functions. The present paper is concerned with establishing a framework for lighting practice and applied research that will assist lighting practitioners and manufacturers in interpreting this emerging research.
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In the late 1990s, CIE began to shift its emphasis from lighting for visibility to a more broad definition of lighting quality, encompassing human needs, architectural integration, and economic constraints (including energy) [41]. 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 aesthetic appreciation. Among other developments, this definition reflects the many demonstrations that there are nonvisual, systemic effects of light in humans. Specifically, controlled laboratory and clinical studies have demonstrated that light processed through the eye can influence human physiology, mood and behaviour. These findings may provide the basis for major changes in future architectural lighting strategies. The report of CIE TC 6-11 summarises the literature in this rapidly-developing area through December 2001, including the neurophysiology, neuroanatomy, behavioural effects of daytime and night-time effects of light exposure in healthy people, and therapeutic effects of light. The report concludes with preliminary guidance concerning healthy lighting and how it might be applied architecturally. This presentation will focus on the possible architectural applications of this area of research, for lighting interiors occupied by day and by night, as a step towards lighting recommendations that respect the broadest definition of lighting quality. Jusqu'à la fin des années 1990, la Commission internationale de l'éclairage (CIE) considérait qu'un système d'éclairage se résumait à la seule visibilité. La CIE a élargi depuis sa vision, et le but de l'éclairage, en introduisant la notion de qualité d'éclairage : outre la visibilité, l'éclairage doit répondre aux besoins personnels, à l'intégration architecturale et aux contraintes économiques (y compris l'énergie) [41]. Dans le cadre des besoins personnels, tels que définis ici, un bon éclairage doit satisfaire la visibilité, la santé, la capacité de travailler, la communication interpersonnelle et l'appréciation esthétique. Outre les autres considérations, cette définition conforte différents témoignages selon lesquels la lumière aurait des effets systémiques non visuels sur l'homme. Plus spécifiquement, des études contrôlées en laboratoire et des études cliniques ont montré que la lumière traitée par l'?il peut influencer la physiologie, l'humeur et le comportement des humains. Ces résultats pourraient servir de base à d'importants changements dans les stratégies d'éclairage architectural. Le rapport CIE TC 6-11 résume les recherches effectuées jusqu'en décembre 2001 dans ce domaine en constante évolution, y compris en neurophysiologie et en neuroanatomie, sur les effets de la lumière du jour sur le comportement, les effets de l'exposition lumineuse dans la nuit et les effets thérapeutiques de la lumière. Les conclusions du rapport contiennent des recommandations sur l'éclairage salutaire et sur la manière de l'appliquer architecturalement. Cet exposé s'attache aux applications architecturales potentielles de ce domaine recherche - l'éclairage d'espaces intérieurs occupés de jour comme de nuit. Une étape vers des recommandations qui respectent la définition la plus large de la qualité d'éclairage. RES
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Sleep disturbances are an all-too-familiar symptom of jet lag and a prime source of complaints for transmeridian travelers and flight crews alike. They are the result of a temporary loss of synchrony between an abruptly shifted sleep period, timed in accordance with the new local day-night cycle, and a gradually reentraining circadian system. Scheduled exposure to bright light can, in principle, alleviate the symptoms of jet lag by accelerating circadian reentrainment to new time zones. Laboratory simulations, in which sleep time is advanced by 6 to 8 h and the subjects exposed to bright light for 3 to 4 h during late subjective night on 2 to 4 successive days, have not all been successful. The few field studies conducted to date have had encouraging results, but their applicability to the population at large remains uncertain due to very limited sample sizes. Unresolved issues include optimal times for light exposure on the first as well as on subsequent treatment days, whether a given, fixed, light exposure time is likely to benefit a majority of travelers or whether light treatment should be scheduled instead according to some individual circadian phase marker, and if so, can such a phase marker be found that is both practical and reliable.
Conference Paper
Everyone has their own personal struggles, and we are in the habit, for better or for worse, of powering through them. But is that the right approach? Sleep deprivation, anxiety, depression, to name but a few, are frighteningly commonplace amongst the general populace. To deny that these conditions exist in the workplace would seem to be foolish. The important question is, is this reality acknowledged? Are there support structures in place to help us address mental health issues when they arise? After all, healthier employees are in everyone's best interest: company, client, and of course, the individuals themselves. This panel will be comprised of members of the SIGUCCS community who currently experience, or have experienced, some form of mental health issue that they feel has had an impact on their professional (and personal) lives. We'll talk about how these conditions manifested themselves, the impact that they had or are having on our work, and what we did or are doing to address them. We'll also talk about the importance of support structures in our workplace, whether they existed in our personal experiences or not. Please join us in what we hope to be a safe environment for an important conversation.
This study has focused on the impact of fluorescent light on endocrine, neurophysiological, and subjective indices of wellbeing and stress. Results from two types of fluorescent lamps, 'daylight' and 'warm-white', were compared, each at two different levels of illuminance. Exposure lasted one day for each of the four combinations. The condition involving 'daylight' lamps with a high illuminance evoked a negative response pattern. The social evaluation of the office space went down, and at the same time the visual discomfort increased. The EEG contained less delta rhythm under the high illuminance conditions. During the day of light exposure the alpha rhythm became attenuated under the 1700 lux 'daylight' lamps. The results warrant the conclusion that fluorescent light of high illuminance may arouse the central nervous system and that this arousal will become accentuated if the lamps are of the 'daylight' type. The practical implication may be that people should not be exposed to fluorescent light of high illuminance for a prolonged period of time.
Long-term behaviour /response of people has been studied in standard window zone offices during daytime working hours. Regular cell-offices were equipped with experimental lighting systems delivering lighting conditions that are known to influence human physiology. The results show that most people prefer to follow a daylight cycle instead of a constant level. Preferred lighting levels are significantly higher than today's indoor lighting standards and correspond to levels where biological stimulation can occur. The results strongly suggest that meeting biological lighting needs is very different from meeting visual needs. Results of two permanent occupants show striking differences in lighting settings, which correspond to individual circadian cycles and performance. This strengthens that present indoor lighting levels (and standards) are too low for biological stimulation. Medical research has shown that a prolonged lack of ‘light vitamin’ can cause health problems ranging from minor sleep and performance difficulties to major depressions. This inevitably suggests that ‘poor’ indoor lighting is the underlying cause of many of the health and performance problems. By naming this the ‘ill-lighting syndrome’ we may well have identified the fundamental mechanism that can result in many different negative health/performance effects. Creating healthy indoor lighting can be a simple form of preventive medicine and providing a new challenge for the lighting community.
Proefschrift--Groningen. Bibliography: p. 76.