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LIGHT AND QUALITY OF LIFE
Chapter to appear in A. C. Michalos (in press). Encyclopedia of Quality of Life Research. Germany: Springer.
Yvonne A. W. de Kort
Eindhoven University of Technology
Eindhoven
The Netherlands
y.a.w.d.kort@tue.nl
Synonyms
Light; Lighting; Indoor lighting; Daylight
Definition
Light is essential to the very existence of life, although much of the time we take it for granted.
On a day-to-day basis, light impacts quality of life significantly and through different pathways.
Light is often used as a means to create atmospheres and can powerfully influence mood and
emotion. Moreover, light impacts alertness, vitality, and performance, entrains our biological
clock, regulates sleep and hormonal processes, and is a crucial determinant of both physical and
mental health. The design of environments that maintain and foster human wellbeing thus
requires careful consideration of both visual and non-visual pathways through which indoor light
– both natural and artificial – impacts quality of life for its inhabitants.
Description
Intuitions about the beneficial effects of light – especially sunlight – date back at least to the
ancient Greek, but many will regard Florence Nightingale as one of the first to explicitly
recognize the importance of light in health care environments. In her ‘Notes on Nursing: What it
is and what it is not’ she argues that light is essential to health and recovery:
It is the unqualified result of all my experience with the sick that, second only to their need of fresh air, is their need
of light; that, after a close room, what hurts them most is a dark room and that it is not only light but direct
sunlight they want.
— Florence Nightingale, 1860, p.47
Although Nightingale’s ideas on the salutogenic effects of light were largely based on
unstructured observations at the time, her insights have indeed been confirmed by a number of
controlled studies performed in clinical settings. In these studies, direct sunlight entering the
room – particularly in the morning – proved effective in decreasing the length of stay for
depressed patients in psychiatric units (Beauchemin & Hays, 1996; Benedetti et al., 2001).
Similarly, spinal surgery patients reported lower levels of experienced pain and stress in more
sunny hospital rooms (Walch et al., 2005). Moreover, patients treated for a myocardial infarction,
showed faster recovery and lower mortality in more sunny rooms (Beauchemin & Hays, 1998, in
a manuscript aptly titled ‘dying in the dark’). These studies demonstrate that sunlight is conducive
to recovery from both mental and physical health problems.
Electric light has also demonstrated therapeutic effects in clinical settings. Its best-known
application is in the treatment of Seasonal Affective Disorder (SAD, or ‘winter depression’).
Based on a review and meta-analysis of randomized controlled trials, Golden and colleagues
(2003) conclude that bright light treatment and dawn simulation are effective for persons
suffering from SAD. The effect sizes were equivalent to those in most antidepressant
pharmacotherapy trials, and effects appeared relatively fast and with minimal adverse side effects.
But application of bright light also shows promise for the treatment of non-seasonal mood
disorders (Terman & Terman, 2005). Its effectiveness in this domain has been established in a
very recent study on elderly patients with major depressive disorder (Lieverse et al., 2011), which
demonstrated that bright light therapy improved mood and enhanced sleep efficiency.
Importantly, the effects of light – natural or electric – on wellbeing extend beyond clinical
settings and pertain also to the healthy population. For instance, Partonen and Lönnqvist (2000)
explored the effects of exposure to bright light on office employees during a field study in winter.
Repeated bright-light exposure improved vitality and alleviated distress both for those with and
without season-dependent symptoms. Hubalek and colleagues (2010) demonstrated that daily
light exposure was positively and significantly related to sleep quality in a healthy population of
office workers. Exposure to bright light can impact mood, increase subjective alertness, improve
cognitive task performance and influence physiological measures of arousal. A higher illuminance
can, for instance, affect hormone secretion, increase heart rate and heart rate variability, and
increase core body temperature (e.g., see Cajochen, 2007). Such effects have been demonstrated
for nocturnal exposure to light, but have recently also been established during the day, under
regular conditions, i.e., in persons who had not been sleep or light deprived before the light
exposure (Smolders & de Kort, 2012).
Although far from comprehensive, the literature discussed above clearly illustrates the powerful
impact light has on subjective and objective mental and physical wellbeing. Its effects range from
improved mood, vitality, alertness, stress relief, and sleep quality, to recovery from depression,
and recovery after surgery. In order to employ natural and artificial lighting to optimize human
functioning, and to formulate crucial requirements for human light exposure – e.g., dose, timing,
spectrum, source – we need to fully understand the mechanisms through which this external
stimulus gets under our skin.
Pathways of light to human wellbeing
Different mechanisms underlie light’s impact on human health and wellbeing. The first category
of mechanisms is referred to as the visual path. Importantly, this visual path not only pertains to
visual performance in terms of, for instance, object recognition, contrast perception or visual
comfort. It also refers to phenomena that are more experiential in nature, e.g., relating to the
strong preferences individuals show towards (brighter) daylight and the positive connotations
they have with natural light and sun (e.g., Galasiu & Veitch, 2006). From a theoretical viewpoint it
is important to note that preferences that exist for environments with windows are naturally
confounded with preferences for a view to the outside, providing among other things
information on weather, season, time of day, social activity and positive distraction. Yet recent
research showed a consistent preference for brighter and sunnier views, even when controlling
for the content of images (Beute & de Kort, 2012). As such, sunlight and daylight can improve
satisfaction, improve mood, and induce positive emotions. In turn, mood and emotion, as core
elements of subjective wellbeing have been related to health in the domain of positive
psychology.
In addition to daylight, the literature indicates that artificial lighting can also influence emotions,
mood, ambiance, aesthetic appreciation, and spatial impressions, although at this time the
collected findings are quite inconclusive, and have only rarely been established outside of the
laboratory. Nevertheless, light is one of the core elements people use to create an ambiance, for
instance at home, in retail or hospitality settings, and beneficial effects are even reported for work
environments (e.g., Kuller et al., 2006).
The strong preference for daylight in workplaces is said to be associated particularly with the
belief that daylight supports better health (Galasiu & Veitch, 2006). To illustrate this point,
studies assessing beliefs about lighting effects, found that over eighty percent of their participants
agreed or strongly agreed that natural light indoors improved their mood. A majority also
reported that the quality of light was important to their wellbeing. People may also hold beliefs
regarding the positive effects of bright or natural light on alertness and performance. Beliefs may
have been fed partially by recent publications on such effects in the popular media, but in fact
such beliefs have existed well before these studies had even been performed (Galasiu & Veitch,
2006). As a supplementary psychological route in addition to preferences, positive mood, and
satisfaction, associations between alerting effects and bright and natural light may unconsciously
influence motivation for and/or effort invested in the task at hand.
A second important category of pathways for light’s effects on health pertains to so-called non-
visual mechanisms. Light has long since been related to the circadian system and acknowledged as
one of the important ‘Zeitgebers’ entraining the biological clock to natural rhythms of light and
dark. Until recently, it was generally assumed that this effect was initiated by the same rods and
cones that help us see the world in all its colorful splendor. This view has been radically changed
by the discovery of the intrinsically photosensitive Retinal Ganglion Cell (ipRGC; Berson et al.,
2002; Sekaran et al., 2003). This third type of photoreceptor cell in the mammalian retina does
not signal to the visual cortex and hence does not contribute to vision as far as we know. Instead,
it projects directly to the suprachiasmatic nuclei (SCN), our internal biological clock, and from
there on influences the production of certain hormones (e.g., melatonin, cortisol), and activates
numerous parts of the brain relevant to alertness. This discovery has contributed to a much
deeper understanding of the neural mechanisms behind the biological clock, and spurred a
significant research effort in this area. Through this research we have come to learn that this non-
image forming photoreceptor is particularly sensitive to light in the short-wavelength, blue part of
the spectrum – not accidentally abundantly present in daylight. Recent research has established
that via this non-visual route light can have both direct and phase shifting effects on the circadian
clock.
Phase shift effects refer to temporal changes in the circadian rhythm. Good entrainment of the
biological clock is essential for good sleep and good mental and physical health. Periodic light –
preferably bright and with high power in the blue part of the spectrum – is necessary for effective
and stable entrainment of our biological clock. A misalignment between the internal circadian
pacemaker and the external environment has been related to problems such as cardiovascular
disease, diabetes, sleep disorders, gastro-intestinal disorders, and possibly cancer (Cajochen,
2007). Although the exact physiological workings behind these effects are not fully understood,
much may be traced back to the importance of good sleep and the well-timed production of
hormones and other bodily processes in alignment with the daily pattern of sleeping, eating,
physical activity, and other behaviors. Nocturnal exposure to light (including late evening and
early morning) can reset the internal clock – forward or backward depending on the exact timing
of the exposure. This may result in the desynchronization of physiological and hormonal
processes with a person’s activity patterns (e.g., Cajochen, 2007). Bright light, administered at the
right time of the day, can realign the internal clock to function in concordance with daily rhythms
and as such support health. These insights are particularly useful in the treatment of sleep and
mood disorders. They also aid in supporting shift workers and other individuals who may be
subject to deregulated circadian rhythms, e.g. during intercontinental travel (jet lag), during
seasons with extremely long or short durations of natural daylight, or due to degenerative
impairments of the visual system (e.g., yellowing of the lens, glaucoma).
Direct effects of light on the human nervous system refer to instantaneous changes in
physiological arousal demonstrated in for instance heart rate and heart rate variability, brain
activity measured with EEG and fMRI, and hormone secretion (melatonin, cortisol). In addition
to these psychophysiological effects, research has shown that exposure to higher illuminance
levels can result in increased subjective alertness. Studies have demonstrated that bright light at
night counteracts sleep pressure and immediately raises alertness, performance on mental tasks,
and the ability to sustain attention. But immediate effects of light have also been demonstrated
during daytime, i.e. when hormonal levels of melatonin and cortisol already support wakefulness
and sleep pressure is low (Smolders & de Kort, 2012).
Reconsidering indoor lighting for Quality of Life
The discovery of the intrinsically photosensitive Retinal Ganglion Cell (ipRGC) has incited a
significant research effort to untangle the exact workings of this new pathway of light into the
brain. Simultaneously, it has raised our awareness of the importance of light, and particularly of
using daylight for the realization of healthy environments. By nature, daylight is intense, powerful
in the short-wave (blue) part of the spectrum, and maximally supports the circadian rhythm
through its availability during the day and absence during the night. Architectural lighting
strategies, which traditionally involved mainly the consideration of energetic issues and of visual
aspects of lighting – aesthetics, visual performance and comfort – should now also explicitly
incorporate the non-visual effects of light in the design of the built environment. This holds
particularly for those environments where people spend considerable amounts of time - at home,
at work, in schools, and in care settings (e.g., hospitals, residential care facilities) – and for user
groups that spend little time outside.
As we have seen, artificial light also contributes to lighting quality. Indoor light standards
currently do not take into account requirements pertaining to the circadian properties, or the
acute alerting and performance enhancing effects of light. Such requirements relate to lighting
spectrum, color temperature, and lighting levels – generally levels of around 1000 lux are advised
for entrainment of the biological clock, at least a few hours a day. Moreover, the direction of
lighting should be considered, as vertical – i.e., directly on the eye – rather than horizontal – i.e.,
on the table or desk – illuminance levels indicate the actual amount of light falling on the retina.
In the majority of current offices the lighting does not satisfy these non-visual lighting criteria. A
large study by Aries (2005) found that in only 20% of offices illuminances over 1000 lux at the
eye were attained; illuminance levels were correlated with employees’ sleep quality (positively) and
fatigue (negatively). Therefore, in addition to requirements pertaining to visual performance,
comfort and aesthetics, lighting levels and light spectrum should be considered with regard to
vital biological mechanisms, supporting the healthy entrainment of employees’ biological clocks
and optimal alertness, vitality and performance. Moreover, light designs should respect the
psychological needs of workers. Preferences for windows and daylight have been well established
in work environments (Boyce et al., 2003), and lighting characteristics have been shown to
improve satisfaction and mood at work (Veitch et al., 2008). Special care needs to be given to the
specification of lighting systems for shift workers, helping them to stay awake and alert for safe
and optimal performance, yet preventing a misalignment between their internal clock and their
activity patterns on subsequent days (Cajochen, 2007).
Evidence of daylight effects on learning, student performance and wellbeing are quite scarce. For
a large part this is due to the extensive set of parameters that vary between schools (e.g., air
quality, noise, the specific school and school site, teacher skills, school socioeconomic status) and
have been difficult to control even in large-scale investigations. Yet although daylight brings some
risks of glare and heat gain, windows that provide sufficient and evenly distributed daylight, and
extensive views to the outside (particularly nature) are likely to make a positive contribution to
student progress (Boyce, 2003). Studies exploring the effects of artificial lighting in schools are
even scarcer. A recent pilot study on effectiveness of variable lighting reported that high
intensities and color temperatures may improve reading speed and concentration (Barkmann,
2012). Moreover, the same manuscript suggests that the opportunity to structure the school day
by selecting different light settings to accommodate the type of activities – e.g. intense blue light
for concentration, lower and warmer light levels for interaction and group work – is generally
appreciated by both teachers and students. Similar applications will need to be investigated on a
larger scale. But as in professional contexts, light and windows are expected to enhance mood,
alertness, vitality and performance, improve sleep quality and lower stress and anxiety.
Striking findings in terms of light’s effects in care environments were already mentioned in the
introduction. They included improved mood and enhanced sleep efficiency, recovery from both
seasonal and non-seasonal depression, faster recovery after surgery, decreased use of pain
medication and even lower mortality rates. Effects were reported for daylight, sunlight and/or
artificial lighting. Importantly, they often did not uncover the underlying mechanisms: some
effects may have been grounded in visual pathways, others in non-visual pathways, others
perhaps in both. But because the inhabitants of these places are either sick, recovering, or frail,
and oftentimes stay there for extended periods of time, care environments present the most
pressing case for good lighting. Moreover, an integrative review of studies relating to ‘healing
environments’ concluded that the only environmental characteristics for which convincing
evidence had been delivered for a psychological effect on wellbeing in care settings were sunlight,
windows, and odor (Dijkstra, Pieterse & Pruyn, 2006). Care environments are also the setting for
innovative and exciting explorations of new light applications: for instance, bright light for
circadian entrainment of dementia patients in residential care, dynamic lighting for de-escalation
and the prevention of segregation in psychiatric care, daylight simulation and artificial skylights
for relaxation, stress relief and better recovery in hospitals.
In a recent brief review centering on home environments, Veitch (2011) concludes that only scant
attention has been given to effects of light in residential buildings, in spite of the growing
literature on the relevance of light for human health. Again, as for work and school
environments, lighting quality in housing should pertain to visual, biological and psychological
mechanisms and particularly consider sufficient levels of daylight, for regular and consistent
provision of sufficient levels of natural light, meeting both circadian needs and user preferences.
Special attention should be given to lighting design for the elderly. Changes in the ageing visual
system render them more sensitive to glare, while at the same time requiring higher lighting levels
both for visual performance and entrainment of their biological clock.
In conclusion
Light impacts quality of life significantly and through different pathways. Although the
psychological and biological pathways that mediate the relation between light and quality of life
have been subject of much research during the past decade, they deserve much more scientific
attention in the future. At the same time, the evidence collected to date sufficiently warrants the
claim that the design of environments that maintain and foster human wellbeing requires the
careful consideration of both visual and non-visual pathways through which indoor light – both
natural and artificial – impacts quality of life for its inhabitants. In short, there is great potential in
leveraging the quality of light to enhance the quality of life.
Cross-References
Built environment
Mental health
Mood
Morningness, eveningness, and life satisfaction
Mortality rates
Nature and wellbeing
Outdoor environments
Pain
Positive psychology
Psychophysiological measures
Restorative environments
Salutogenesis
School climate
Season effects
Sleep
Stress
Subjective well-being
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