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Lighting - to your good health = Lyset og det gode helbred
Veitch, J. A.
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Arkitekten, 9, pp. 60-63, 2007-09-01
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Lighting – to your good health = Lyset og det
gode helbred
NRCC-49682
Veitch, J.A.
A version of this document is published in / Une version de ce document se trouve dans:
Arkitekten, no. 9, Sept. 2007, pp. 60-63
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Lighting – To Your Good Health
Jennifer A. Veitch, Ph.D.
NRC Institute for Research in Construction
[email protected]
Abstract
Many lighting designers and researchers see exciting possibilities in the mounting discoveries concerning
physiological functions that light and darkness influence. Our daily exposure to light and darkness
influences circadian cycles of hormone release, bodily functions, and activity. This knowledge has led to
light treatments to help shift workers and people with sleep disorders. Some argue that new forms of
interior lighting might improve the health and well-being of people in everyday environments, and that
updated lighting recommendations should have this aim. So far as is currently known, chief among the
implications is the importance of daylighting, which means that sustainability and healthy lighting are
congruent goals.
Lighting – To Your Good Health
Recent years have brought new excitement to lighting research, and new efforts to connect with lighting
designers. Two related developments are the basis for these changes:
The first development, in the mid 1990s, saw the adoption of models of lighting quality, which integrate
human needs, architectural integration, and economic constraints (including energy) (Figure 1), as
organizing principles for lighting recommendations. Good lighting must simultaneously satisfy all these
dimensions. The human needs incorporate vision and the avoidance of visual discomfort, but also
demand attention to lighting for the maintenance of good health, task performance, interpersonal
communication, and aesthetic appreciation. One mark of the value of this model is its appearance in the
9th Edition IESNA Lighting Handbook (2000) as the organising framework for the new Lighting Design
Guide. (The Illuminating Engineering Society of North America, IESNA, is the principal North American
body for lighting recommendations and standards.)
Figure 1: Lighting quality requires the integration of individual well-being, architecture, and economicenvironmental dimensions.
The second development is the newfound excitement for understanding the effects of light on human
physiology and health. Although research in this area has a long pedigree, the discovery of new
photoreceptors – retinal cells that detect light – surprised the photobiology world in 2001. Researchers
© 2007, Her Majesty the Queen in Right of Canada. National Research Council, Ottawa, Canada K1A 0R6.
Originally published in Danish as “Lyset og det gode helbred” in Arkitekten magazine, 09/07, pp. 60-63, Sept. 2007.
Translation by Lars Nevald.
had thought that they knew everything there is to know about the retina: that rods and cones detect light
and send signals to the brain that are decoded to produce visual perception. Now, it is clear that that
there is a separate set of retinal receptors, a special subset of the ganglion cells, that detects light and
sends signals to the brain. It seems to be a small number of cells, spread all over the retina, and with
connections to a wide variety of brain structures. These cells detect only light and darkness, and the
information they send synchronizes many bodily functions with these external conditions.
The pathway from the retina to the pineal gland, which secretes melatonin, has received the most
research attention. Melatonin is one of many hormones that rise and fall in a daily cycle. It is released at
night, during darkness, and is a hypnotic that regulates activity-sleep cycles and core body temperature,
among many other physiological functions. During the day, there is almost no melatonin secretion. Good
health requires a regular rhythm of melatonin and other hormones, each rising and falling in its turn.
Healthy lighting, then, includes healthy darkness.
Bright light exposure at night suppresses melatonin, increasing alertness and lowering sleepiness. This
phenomenon has helped to demonstrate that there are separate visual and non-visual pathways from eye
to brain. Previously, we knew of two spectral sensitivity curves that described the eye’s response to light
of varying wavelengths: V , with its peak at 555 nm (yellow-green) was the response with the eye adapted
to bright light (photopic) and V’ , with its peak at 505 nm (blue-green) was the response in dark adaptation
(scotopic). To these we can now add a new curve, which does not yet have a name, and whose shape is
still the subject of study, but which peaks around 460 nm. Figure 2 shows the results from studies of the
suppression of melatonin following light exposure at night in two laboratories (Thapan et al., in the UK,
and Brainard et al., in the USA), which agree on the general shape and the location of the peak. The
newly-discovered retinal receptors appear to respond most strongly to short-wavelength light, and in a
clearly different pattern than the visual sensitivity curves that have long been known. Thus, we can
deduce that different light detectors are involved in melatonin suppression than in vision.
Figure 2. Spectral sensitivity curves show us how the eye responds to
different wavelengths for various functions.
The effect of bright light on melatonin suppression has also led to useful applications: Work from several
labs has shown that resetting a maladjusted circadian rhythm – such as one experiences when flying
across time zones, or working a night shift – can be achieved with intermittent bursts of 20 minutes
exposure to 1200 lux white light, provided that the exposures are properly timed and the individual avoids
light exposure during non-working hours. This is an important advance because the solution does not
require energy-intensive additions to room lighting, as had previously been thought. Ongoing
experimental work tests the effectiveness of using very high correlated colour temperature lamps (CCT~
17000 K), which are rich in the short wavelengths to which these photoreceptors are most sensitive;
these might produce the same benefits either with shorter exposures or lower energy use, which would
make them still more practical.
Epidemiological studies of shift workers have observed that people who work night shifts are at greater
risk of breast and other cancers. One hypothesis that might explain this is disruption to melatonin
rhythms. Melatonin has been shown to prevent cancer cell growth in cell cultures and in animal models.
Most recently, a team of US researchers tested the hypothesis experimentally and found that rats who
received the highest melatonin doses showed the least tumour growth. This finding reinforces the
importance of a regular rhythm of light and dark for everyone, so that there is a regular rhythm to the rise
and fall of melatonin and other hormones.
For night-shift workers, this may mean that permanent, or at least slowly-rotating, shift schedules are
more healthy, because they allow hormones, melatonin among them, to have a regular daily rise and fall
— again, provided that there is a period each day of light exposure and a period of darkness. Light at
night during the night shift can help to maintain work performance and alertness; light avoidance by day
provides better sleep and the opportunity for melatonin secretion and its physiological benefits. Timing is
everything, however; expert advice is needed to fit the light exposure to the shift schedule so that all the
rhythms are appropriately adapted.
Most people, of course, work the day shift. How can the new research help them? Research in this area is
in very early days. However, correlational evidence suggests that healthy people who receive little light
exposure each day experience more symptoms of depression than those who receive higher light
exposures. Experimental evidence from Finland shows that modest increases to daily light exposure (e.g.,
exercising in a gym lit to 2400 lx instead of 600 lx, for one hour three times a week) can improve feelings
of vitality and well-being. Whether or not this effect occurs through the same pathway as melatonin
regulation is unknown, and we are a long way from knowing how much light exposure, of what
wavelengths, at what time of day, is needed for optimal physical and mental health.
The lighting practitioner community is eager to incorporate lighting and health concepts into lighting
recommendations. The fact that short-wavelength light is most effective for melatonin suppression, and
the evidence that people can benefit from some bright light exposure every day, lead to an obvious
design conclusion: Daylighting is one way to provide healthy lighting in buildings (Figure 3). It is energyefficient, rich in short-wavelength light, and available much of the time at high intensities. Lighting for
sustainable design can also be lighting for good health.
Figure 3. Daylighting is one way to ensure that people have opportunities to get daily bright light
exposure.
Health care settings are among the obvious first targets for applications of lighting and health research.
For example, facilities for Alzheimer patients seek ways to reduce night restlessness among patients,
which is a serious problem for caregivers and patients alike. Two small studies have shown that exposure
in the late afternoon or evening to bright blue light from light-emitting diodes (LEDs), as compared to dim
red LED light, reduced the frequency of patients’ early-morning waking. Other studies among nursinghome residents in varying states of health have found that increasing the general illuminance level in
lounge areas can reduce night restlessness. The Commission Internationale de l’Eclairage (CIE) has a
technical committee, TC 3-44, currently engaged in preparing a design guide on lighting for the elderly
that will incorporate these and other findings.
Some have characterised lighting and health as causing a revolution in lighting. Whether this is true or
not, remains to be seen. Certainly, lighting researchers have no shortage of research directions to follow!
Lighting designers and industry have more reason than ever to follow the latest research results over the
next several years, as we understand more about how to improve well-being and health using light and
lighting.
Jennifer Veitch is a Senior Research Officer at the National Research Council Canada Institute for Research in
Construction (NRC-IRC). NRC-IRC is the principal governmental research and development laboratory for the
Canadian construction industry. Through its research and in partnership with industry, the Institute works to improve
the safety, durability and comfort of Canadian workplaces, homes and public infrastructure (http://irc.nrc-cnrc.gc.ca).