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Lighting for well-being: a revolution in
lighting?
NRCC-49205
Veitch, J.A.
A version of this document is published in / Une version de ce document se trouve dans:
Proceedings of the 2nd CIE Expert Symposium on Lighting and Health, Ottawa, Ontario,
Sept. 7-8, 2006, pp. 56-61
Co
py
ri
g
ht Notice
/ Droits d'auteur
Originally published in the Proceedings of the 2nd CIE Expert Symposium on Lighting and Health
(CIE x031:2006, pp. 56-61). Vienna, Austria: CIE.
LIGHTING FOR WELL-BEING: A REVOLUTION IN LIGHTING?
Jennifer A. Veitch, Ph.D.
National Research Council of Canada, Institute for Research in Construction
Ottawa, Ontario, Canada
ABSTRACT
A model of lighting quality proposed in
the 1990s defined good lighting as that
which balances the needs of humans,
economic and environmental issues, and
architectural design. The model made
explicit what had long been implicit: Lighting
is not just about seeing details. Good
lighting provides for the needed level of
visual performance, but also determines
spatial appearance, provides for safety, and
contributes to human health and well-being.
Far from being a revolutionary proposal,
lighting for everyday well-being has long
been a goal of lighting recommendations.
The question for today is how quickly we
should incorporate new research findings in
revisions of recommendations. This paper
will address the knowledge base and the
state of lighting recommendations for three
aspects of interior lighting that contribute to
health and well-being: areas of high
luminance (about which much is known, but
more to be learned); luminous modulation
(flicker) (about which we have some
knowledge); and, total daily light exposure
(about which knowledge is weak, but
suggestive). Appropriately,
recommendations are most specific for
those areas about which knowledge is
strongest. Revisions should keep pace with
evolving knowledge, but not run ahead.
1. INTRODUCTION
The World Health Organization has
defined health as follows: “…a state of
complete physical, mental, and social well-
being and not merely the absence of
disease or infirmity” [1]. Although some have
argued that this definition is too broad, it has
the merit of being both negative (not a
disease state) and positive (a state of
complete fitness and contentment). My
contention here is that lighting installations
can, and do, contribute to both states. The
question we face today is to what extent,
and how quickly, we will modify our
recommendations to take into account new
science concerning light effects on human
physiology and psychology.
Figure 1 shows a model of lighting quality
that appeared in the 2000 edition of the
IESNA lighting handbook [2], and which is
consistent with discussions at the First CIE
Symposium on Lighting Quality here in
Ottawa in 1998 [3]. It represents a major
change in thinking about lighting design, a
shift away from the dominance of visual
performance as the chief goal for a lighting
installation. Individual well-being for the
people in the space – all the many and
various needs of all the different people who
encounter the lighting installation – is among
three dimensions of good-quality lighting.
Visibility (seeing fine details) remains an
essential part of any lighting installation, but
is not the only purpose of the installation.
Figure 1. Lighting quality model. From
Veitch (1998), courtesy of the National
Research Council of Canada.
One example of how this new model
might be applied is evident in the report of
CIE's technical committee TC 6-11 [4]. The
© 2006, Her Majesty in Right of Canada. National Research Council Canada, Ottawa K1A 0R6
page 2 of 6
report was the first review of the literature on
light, lighting and health, and made the first
attempt at formulating principles of healthy
lighting together with preliminary
suggestions for achieving healthy lighting
within the framework of good-quality lighting.
Two of the five principles are particularly
relevant to this paper:
• The daily light dose received by
people in Western countries might be too
low.
• The important consideration in
determining light dose is the light
received at the eye, both directly from the
light source and reflected off surrounding
surfaces.
The science of light effects on human
physiology and psychology is moving
rapidly; for example, the TC 6-11 report
included an appendix with citations to 58
original research papers published between
the close of the literature review phase and
the final editing of the report (January 2002
– November 2003) [4]. Further advances
were reported in Vienna in September 2004
at the 1st CIE Symposium on Light and
Health, which was attended largely by the
scientific community [5]. Now, at the 2nd CIE
Symposium on Lighting and Health, the
challenge for lighting applications people is
to consider how this work might change
lighting recommendations.
Some have considered this to be a
revolution in lighting [6]; others are more
cautious in their excitement [7,8]. In this
paper I review three ways in which lighting
can influence well-being, with the aim of
demonstrating that lighting practice has long
addressed well-being in at least a limited
way. The question before us now is not
whether to use lighting to influence health
and well-being, but which specific effects
have sufficient scientific support to change
recommendations now. These three aspects
of well-being are not the whole picture, but
they illustrate the progression of knowledge
that one hopes will arise from prolonged
investigation.
2. LIGHTING AFFECTS WELL-BEING
2.1 Direct Glare
Direct glare has a long history in the
lighting research literature [9,10,11]. By
“direct glare” I mean unwanted light shining
directly into the eye (or glancing off the
cornea, in the case of what's been called
"overhead glare"). This is an instance in
which lighting recommendations already aim
to provide well-being; in this case,
prevention is the goal. The phenomena are
somewhat well-understood, have been
studied for decades, and have resulted in
the adoption of predictive models in
recommendations [12,13].
There are two dominant predictive
models: Visual Comfort Probability (VCP)
[12] and Unified Glare Rating (UGR) [13].
Although the models differ in their details,
both predict the discomfort experienced by
viewers as a function of luminaire
luminance, adaptation luminance, luminaire
position and luminaire size. VCP is less
commonly used today, but UGR limit values
are a feature of CIE’s standard for lighting of
interior workplaces [14].
Nonetheless, there remain unanswered
questions, and reasons to think that the
models might not be the best predictors of
discomfort in real settings. Glare from
daylight induces less discomfort than would
be predicted from the electric lighting
models [15]. Little attention has been paid to
evidence that psychological variables (for
example, task involvement [16]) influence
discomfort, or to evidence that view content
influences discomfort [17,18]. Wide
individual differences in discomfort also
have received little research attention [16].
Lighting recommendations that aim to
reduce direct glare do so in order to
preserve well-being, despite these gaps in
knowledge. There is room for improvement,
but no one would recommend that we ignore
direct glare in lighting recommendations
because of the need for improved models.
2.2 Flicker
Luminous modulation of light source
output, or flicker, is an example of a lighting
dimension for which the evidence of effects
on well-being is reasonably strong but which
receives little emphasis in lighting
recommendations.
Several studies have found that low-
frequency luminous modulation, as from the
operation of fluorescent lamps on magnetic
ballasts (~100 – 120 Hz operation), can
page 3 of 6
interrupt saccadic eye movements [19,20],
reduce visual performance [21,22], and
increase the incidence of headache and
eyestrain [23]. High-frequency operation, as
when electronic ballasts with an operating
frequency on the order of 40 kHz are used,
improved well-being in these studies. It is
thought that the effect is caused by
meaningless neural signals in phase with
the lamp operation that impede cortical
functioning [24]. That is to say, there can be
a sensory response to low-frequency flicker
even when the luminous modulation is not
perceived.
Although several studies have found
deleterious effects of flicker, not all have
been successful. Küller and Laike [25] found
only that individuals with a low critical flicker
fusion frequency showed the effect, raising
the possibility that individual differences
moderate the effect. The effect may diminish
with age [26].
The principal lighting recommendations
documents do discuss flicker and
recommend the use of high-frequency
control gear for discharge lamps in order to
promote well-being [2,14,27]. However, it
may be said that there is little emphasis
given to this aspect of well-being. For
example, flicker is rated as not important to
reading in the Lighting Design Guide of the
IESNA Lighting Handbook [2], and the topic
rates a scant paragraph in the equivalent
CIE document [14]. Reading the technical
magazines one obtains the impression that
energy savings, not improvements to well-
being, are more likely reasons for the
adoption of electronic over magnetic
ballasts.
2.3 Daily Light Dose
This topic is more controversial: The
suggestion that people in industrialized
countries receive too little total light
exposure each day. Although this was
expressed as a principle in the CIE report
[4], it is a novel suggestion based on a
comparatively small research foundation
and one which raises many questions.
One key study surveyed 106 middle-
aged adults in San Diego, California [28],
measuring daily patterns of light exposure
and combined with self-reported mood. The
median person spent 4% of each 24 hr in
illumination greater than 1000 lx, and more
than 50% of the time in illuminance levels
from 0.1 to 100 lx. The questionnaire results
showed a moderate correlation between
atypical seasonal affective disorder
symptoms and time in bright light (r=-.27).
This suggests that inadequate light
exposure is associated with depressed
mood, but does not establish a causal link.
Older adults in New York City
participated in a similar study, to which
detailed ophthalmologic measurements
were added [29]. The total daily light
exposure was low, although it is difficult to
compare the two studies because the NYC
study reported only that the median daily
illuminance was 518 lx. Those with higher
daily light exposure had less depressed
mood; however, the correlation was reduced
when ophthalmologic problems were added
to the equation. The authors suggested that
people with ophthalmologic problems
experience lower retinal illuminance than
healthy people, and therefore derive less
benefit from light exposure.
Studies in Finland have found that
modest increases in light exposure can
improve feelings of vitality in healthy adults
[30,31,32,33]. In several studies they
delivered the light exposure (2400-4000 lx
vs 400-600 lx) in a gymnasium while
participants exercised for one hour two to
three times a week. In general, all the
participants became more fit than a
relaxation-training control group, but the
bright-light group showed a bigger
improvement in mood and mental health
scores over the 8-week study period.
However, the beneficial effect seems to rely
on continued exposure: 4 months later, the
people who had received the bright light
(which had stopped after the 8-week study
period) showed the biggest declines [30].
Overall, these studies are interesting
because they suggest that a relatively
modest increase in light exposure (both in
terms of intensity and duration), delivered
during other activities, might improve well-
being.
At the First CIE Symposium on Light and
Health, Noguchi reported on two small
experiments into increasing light exposures
in an office [34]. In these two experiments,
the authors boosted light exposure for part
of the morning and afternoon, from 750 lx to
2500 lx, and observed trends in
page 4 of 6
physiological and self-report measures
suggesting that the higher light exposure
increased alertness and modified
physiological indices of circadian rhythms.
Although inconclusive, the findings are
suggestive enough to warrant further
research. They also highlight a reason for
there being little work of this type: The
physiological measurements are both
intrusive and expensive, making it very
challenging to track changes over a day,
and then cumulatively over time.
The evidence that increasing light dose
can improve mood and feelings of well-being
in healthy adults is fairly strong; the Finnish
studies were randomized, controlled trials
that set a high standard for causal inference.
However, none of the studies has provided
enough information to form the basis for
lighting recommendations. In particular,
there is no systematic work that has
established the light dose (its intensity,
spectrum, duration, and timing) required for
good health. None of the studies cited here
specified the light exposure in terms of light
received at the eye, and all reported
photopic illuminance, which is an
inappropriate weighting of radiant energy for
non-visual processes [4]. As a result, it is
impossible to precisely calculate how much
light triggered the beneficial responses.
Without this information we cannot establish
even the most simple design goals.
We also know too little about the
physiological mechanisms behind the
observed effects. It is unlikely to be
melatonin suppression, because there is
very little circulating melatonin during the
daytime periods when the experimental
exposures were received. Thus, lighting
interventions to modify circadian rhythms
are probably not appropriate to influence
general feelings of well-being.
Furthermore, we do not know whether
light exposure follows the principle of
reciprocity: Is a longer exposure at a lower
intensity equivalent to a shorter exposure at
a higher intensity? What is the appropriate
time-of-day for the light exposure? What is
the spectral sensitivity curve for this
response? All of these questions require at
least a preliminary answer before
considering the creation of lighting
installations to deliver an increased light
dose.
3. CONCLUSIONS
Great excitement has arisen in the
lighting community because advances in
photobiological science have provided
unexpected insights into fundamental
processes, insights that will probably change
interior lighting recommendations. However,
this is not a revolution: Lighting
recommendations already aim at providing
for health and well-being of occupants,
where the evidence base warrants. Future
revisions of lighting recommendations
documents will continue the evolution
towards high-quality lighting that integrates
individuals’ well-being, architectural goals,
and economic and environmental
constraints.
In considering how to apply the latest
scientific insights to lighting practice, we
must remember that much of the recent
work into light and lighting effects on health
stems from research into the effects of light
on melatonin suppression and release, and
the associated consequences for circadian
rhythms. Figure 2 shows that the neural path
from the retina to the pineal gland is not the
only route for retinal information about light
and dark [4]. These several other pathways
await more thorough investigation. Despite
all the important advances thus far, we are a
long way from having all the answers about
how light affects physiology and psychology.
Figure 2. Light information pathways from
eye to brain. From CIE 158:2004, courtesy
International Commission on Illumination
(CIE).
Lighting practitioners and applied lighting
researchers (the “lighting community” –
designers, industry, researchers, educators)
together have a role to play in developing
the necessary knowledge base. We need
substantial evidence to warrant changes to
recommendations; but we cannot expect
page 5 of 6
basic science to provide the necessary
evidence without our input and participation.
Many scientists who study fundamental
processes lack the understanding of the
information needs of the lighting community
and the motivation to work on applied
questions. Advances of the required type will
occur only through interdisciplinary
research, and only if promoted by the
lighting community [35].
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CONTACT
Jennifer A. Veitch, Ph.D.
National Research Council of Canada
Institute for Research in Construction
Building M-24, 1200 Montreal Road
Ottawa, ON K1A 0R6 Canada
tel. +1-613-993-9671
fax +1-613-954-3733
e-mail: jennifer.veitch@nrc-cnrc.gc.ca