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The importance of light to health and well-being

Authors:

Abstract

Senior Researcher, the VELUX Group The design of well-lit environments is likely to become more and more complex. Traditionally, lighting designers have concentrated on creating lighting conditions that are suitable for the visual tasks performed in a room and simultaneously meet individual needs. This must also support a good interplay between the light from windows and the light from electric lighting, and a wise balance between the intensity of the light used its location and direction. And the light in a room should neither restrain nor impede our ability to see, thus allowing us, at all times, easily to orientate ourselves and move freely around in the rooms and the building. Recent research, however, indicates that the lighting environments of the future must also take into account other factors, such as health issues 1-3. How this can be incorporated into the lighting design of a well-lit environment, though, remains unexplained. What is quite certain is that lighting environments have a direct influence on the health and well-being of the people living and working in them. Circadian rhythms and habits Research has shown that the variation of light is by far the most important factor in setting and maintaining our natural daily rhythm, the so-called circadian rhythm. We should be exposed to intense light in the daytime and preferably sleep in darkness at night. Outdoor daily light exposure will have a significant effect on maintaining our circadian rhythms, but the reality is that we spend 80 to 90% of our time indoors 4-6 ; a consequence of which is that many people are exposed to very low light-doses for long periods of the year. Preliminary evidence suggests that low light-exposure is associated with diminished health and well-being and it can lead to reduced sleep quality, depressed mood, lack of energy and reduced social relations. When we sleep well – and in complete darkness-we produce melatonin; but if we are exposed to light at night, the production of melatonin is suppressed 7. Research has shown that exposure to shortwave length-at the blue end of the spectrum – suppresses our production of melatonin. Night-time outdoor lighting and indoor light sources, especially light sources with high colour temperature ('cool-white' light sources) may have an impact on our sleep quality and natural melatonin secretion. The long-term effect of light exposure at night is not fully understood, but a number of studies 8 indicate a possible connection between light at night and a greater incidence of breast cancer among people who do shift work. Seasonal affective disorder (SAD) Seasonal affective disorder (SAD), also known as winter depression or winter blues, is a form of depression that occurs more frequently in the winter months, typically arising in the autumn and disappearing in the spring. SAD will increase in incidence with increasing latitude. A milder form of seasonal mood disturbance is called sub-syndromal SAD (or S-SAD).
March 2011
The importance of light to health and well-being
By Jens Christoffersen, Ph.D., Senior Researcher, the VELUX Group
The design of well-lit environments is likely to become more and more complex.
Traditionally, lighting designers have concentrated on creating lighting conditions that
are suitable for the visual tasks performed in a room and simultaneously meet
individual needs. This must also support a good interplay between the light from
windows and the light from electric lighting, and a wise balance between the intensity
of the light used its location and direction. And the light in a room should neither
restrain nor impede our ability to see, thus allowing us, at all times, easily to orientate
ourselves and move freely around in the rooms and the building. Recent research,
however, indicates that the lighting environments of the future must also take into
account other factors, such as health issues
1-3
. How this can be incorporated into the
lighting design of a well-lit environment, though, remains unexplained. What is quite
certain is that lighting environments have a direct influence on the health and well-
being of the people living and working in them.
Circadian rhythms and habits
Research has shown that the variation of light is by far the most important factor in
setting and maintaining our natural daily rhythm, the so-called circadian rhythm. We
should be exposed to intense light in the daytime and preferably sleep in darkness at
night. Outdoor daily light exposure will have a significant effect on maintaining our
circadian rhythms, but the reality is that we spend 80 to 90% of our time indoors
4-6
; a
consequence of which is that many people are exposed to very low light-doses for
long periods of the year. Preliminary evidence suggests that low light-exposure is
associated with diminished health and well-being and it can lead to reduced sleep
quality, depressed mood, lack of energy and reduced social relations.
When we sleep well – and in complete darkness - we produce melatonin; but if we are
exposed to light at night, the production of melatonin is suppressed
7
. Research has
shown that exposure to short-wave length - at the blue end of the spectrum –
suppresses our production of melatonin. Night-time outdoor lighting and indoor light
sources, especially light sources with high colour temperature (‘cool-white’ light
sources) may have an impact on our sleep quality and natural melatonin secretion.
The long-term effect of light exposure at night is not fully understood, but a number
of studies
8
indicate a possible connection between light at night and a greater
incidence of breast cancer among people who do shift work.
Seasonal affective disorder (SAD)
Seasonal affective disorder (SAD), also known as winter depression or winter blues, is
a form of depression that occurs more frequently in the winter months, typically
arising in the autumn and disappearing in the spring. SAD will increase in incidence
with increasing latitude. A milder form of seasonal mood disturbance is called sub-
syndromal SAD (or S-SAD).
March 2011
Typical SAD symptoms are emotional depression, lack of energy, increased need for
sleep, increased irritability, increased appetite and weight gain, reduced immune
system activity and often also periodic reduced performance and productivity.
The incidence of sub-SAD is estimated to be two to three times higher than SAD. The
primary treatment of winter depression is light therapy – there are special lamps on
the market for the purpose. Research
9
has also shown that exposure to daylight
outdoors (~ 1000 lux) can reduce SAD symptoms; and as sub-SAD is relatively
common, the amount of daylight in our homes or workplaces can be of considerable
significance – though the effective value of daylight will depend on the architectural
design of a room and the facade
10
.
Health dependent on lighting environment
Should there be significant changes in the building practices of today or should we
just put more conscious thought into the design process? Crucial decisions affecting
daylight conditions are often made at the very early stages of a project. With the
knowledge that the building floor plan and facade is rarely changed in a building’s
lifetime, the design of a building should be determined by the room layout behind the
facade and the activities that go on there. Besides, architects looking to incorporate
this new knowledge of the link between light and health into their building designs will
encounter considerable barriers; available information is often complex and
researchers rarely pass on their findings to architect level, which means that even if
information is available, there is a danger that it will be applied incorrectly
11,12
.
Creating a good visual environment requires an understanding of the function and
capabilities of the visual system, insight into visual perception and knowledge of the
basic properties of light. These include knowledge about adaptation (the eye’s
adjustments to ambient light levels), spectral (colour) characteristics, composition of
diffuse and direct light, brightness contrast or luminance gradient etc. Nor should
attention be given exclusively to the illumination of an object supporting the central
vision (fovea) – the surroundings must be adequately lit as well (peripheral vision).
Peripheral vision contributes to an impression of the surroundings in which we find
ourselves – space dimensions and shape, ambience, materials and light distribution.
For example, the interpretation of peripheral vision information is made easier when
light casts shadows that give visual clues of the shapes in a room – and is made more
difficult when light is uniform. Vertical surfaces in a room often receive more light
from the windows than the horizontal surfaces, whilst the opposite is often true for
artificial light. Because the biological effect of light is affected by the amount of light
in the eye, the difference in contribution within the room between daylight and
artificial light is important. For example, deep rooms and work stations placed too far
from a window could have implications for our health with inadequate daylight levels
all year round.
Adequate lightning
If the lighting of a space is unsuitable or inadequate and makes it difficult to see
properly, it will influence our performance (the visual system) but also can affect our
health (the circadian system) and well-being (the perceptual system). It can result in
unnecessary eye strain and give rise to symptoms such as eye irritation, fatigue and
March 2011
headache. Lighting conditions that can cause these symptoms are poor brightness
contrast, high luminance differences and flickering etc.
Adequate lighting is important for a person’s well-being. Daily working life often
consists of changing visual tasks, with similarly changing demands on the lighting
provided. By supplementing general lighting (daylight and artificial lighting) with task
light, people’s needs can often be met and potential physical and mental irritation can
be avoided or reduced. The need for higher light levels increases with age and elderly
people often need more than twice the amount of light than young people to perform
the same task.
Lighting requirements in different scenarios
Whenever possible, daylight should meet daily lighting requirements, and artificial
lighting should be planned to create the right conditions in those times of the day
when daylight is inadequate. Furthermore, it is likely that artificial lightning should be
‘thought into’ a 24-hour cycle, in which there is a need for one lighting scenario during
the day and another at night. Several studies
13,14
have shown that people prefer
daylight to artificial lighting at work. This is often linked to daylight’s dynamic
variation of intensity, colour and direction and the positive effect these have on our
experience and mood. Canadian studies show that there is a general perception that
daylight should be the primary light source for the sake of our health and well-
being
15,16
.
The importance of a view
A view to the outside is also important for the same reason – it is important to be able
to see out of the window (a view) and have something pleasant to look at (a good
view). One challenge of the future, therefore, might be a greater requirement for a
more flexible lighting plan that takes into account changing work tasks and individual
preferences and needs.
Knowledge of today: facts about the visual system
We have known for a long time that the eye registers change in light and colour
through two classes of light-sensitive photoreceptors in the retina. Our normal ‘day-
vision’ is provided through the colour-sensitive cones (about 8 million) that are
subdivided into three cone photoreceptors, each with its own spectral sensitivity –
blue (S - short wavelength), green (M – medium wavelength) and red (L – long
wavelength) light; the blue-sensitive cells are less sensitive than the other two. Rods
(about 120 million) are more sensitive to light-dark contrasts.
In 2002, a new class of photoreceptor was discovered; a specific subtype of retinal
ganglion cells - ipRGCs (intrinsically photosensitive retinal ganglion cells)
17
. These
ipRGCs comprise about 1-3% of the ganglion cells in the eye, and their sensitivity to
light involves the photo pigment melanopsin. The ipRGCs are most sensitive in the
lower end of the visible spectrum (peaking around 459-484 nm
18,19
), whilst the other
light sensitive photoreceptors are sensitive in other parts of the spectrum
20
. The
interesting thing about these light-sensitive ganglion cells is that they transmit signals
to other parts of the brain than do the rods and cones; one of the effects of these
signals is to help control the circadian rhythm – the biological clock. This is done via a
specific neural pathway from the eye to the suprachiasmatic nucleus (SCN). This
pathway generates physiological and behavioural circadian rhythms such as the
March 2011
sleep/wake cycle, temperature and hormone secretion. The average human circadian
cycle is a little longer than 24 hours and varies from 23.9 hours to 24.5 hours
21
. The
synchronisation of our body clock to a 24-hour cycle is provided by external time-
givers, known by the German word zeitgebere. One very important zeitgeber is the
morning light. There are other external time markers but daylight’s characteristic
light/dark variation, continuity and spectral composition are excellent synchronisers of
our circadian rhythm. The SCN sends information to the pineal gland to produce
hormones such as melatonin. This hormone is an important time-marker and plays a
role in the regulation of circadian rhythm and the coordination of a number of
biological processes
21
. Secretion of melatonin is triggered at a certain light level, being
stimulated by dark and suppressed by light. Body temperature and cortisol production
also show characteristic circadian variation.
Quite how light affects the visual system or circadian rhythm can be divided into five
functions; intensity, spectrum, timing, duration and spatial distribution (the
distribution of the light-sensitive receptors in the retina - see above). Each factor has
a different effect visual and circadian system; for example, most people are able to
read and work with a daily light level of 500 lux, but one hour’s exposure to 500 lux
may not be enough to trigger the circadian rhythm (intensity). The visual system
reacts to and processes light impulses in a fraction of a second, whilst the biological
clock needs minutes or hours (duration). The light that is important to our circadian
rhythm is different from the light that is important to our visual system because of the
spectral difference in the light sensitivity of the individual photoreceptors. The time of
day at which light is registered on the retina (phase response curve) also has a clearly
different effect on the visual system and circadian rhythm (timing). Exposure to
intense light in the morning can reset the biological clock to an earlier time (“get up
earlier”), whilst in the evening it sets it to a later time (“get up later”). This is, in
essence, the syndrome of jetlag, caused by a conflict between the biological time of
day and the geographical time of day. The visual system reacts identically whatever
the time of day.
The research of tomorrow – energy savings and health
So far, research has shown that we have considerable insight into how the intensity,
time, duration, spectrum and distribution of exposure to light affects human behaviour
and physiology – but we cannot describe exactly what conditions, or combination of
conditions, will lead to ‘optimum’ health and well-being
22
. However, we do know that
the impact of light on people will lead to new alliances between researchers from
various scientific disciplines (physiology, psychology, medicine and physics, for
example) and architects
1,2,23,24
. The result will certainly produce rational
recommendations for how we can integrate energy saving with lighting quality, health
and well-being.
References
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