licht.wissen 19 - LightingEurope

Transcription

licht.wissen
Impact of Light on Human Beings
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licht.wissen 19 _ Impact of Light on Human Beings
01
Contents
3 Editorial
34 Practical example: Dynamic retirement
home lighting
5 Human evolution is shaped by light
6 Biological rhythms
[Cover] The brain synchronises our internal
clock with the outside world. One of the cues
it uses is light.
[01] Biologically effective lighting provides
a needs-based supplement to incident daylight.
[02] Particularly important during the dark
months of the year: biologically effective lighting helps compensate for the weaker daylight
stimulus indoors.
37 Practical example: Dynamic domestic
lighting
11 Our internal clock
38 Lamp spectra
15 Biologically effective light
40 Outlook: Research intensifying
16 Biologically effective light indoors
42 Glossary
20 Light therapy
44 Standards, literature
24 Lighting design
46 licht.de publications
26 Lighting quality and energy efficiency
47 Imprint and acknowledgments for
photographs
29 Practical example: Dynamic office
lighting
30 Practical example: Dynamic industrial
workplace lighting
32 Practical example: Dynamic school
lighting
02
Editorial
Light and dark, hot and cold or the cyclical change of the seasons: the rotation and inclination of the Earth give rise to constantly recurring changes that, in the course of evolution, have
resulted in human beings developing a circadian system – a
system of internal clocks that anticipate such changes. Like the
complex movement of a clock, it controls and coordinates the
24-hour variation of all bodily functions. Disrupting it can have a
variety of negative effects, producing symptoms of disorders
such as depression or immune disease.
Scientists have been studying the biological impacts of light perceived by the human eye since as long ago as the 1980s. But it
was not until 2002 that they discovered ganglion cells in the
retina of mammals that are not used for “seeing”. The newly
identified cells respond most sensitively to visible blue light and
set the “master clock” that synchronises the system of internal
clocks with the external cycle of day and night.
namic light. Basically speaking, this means bringing daylight indoors and using artificial light with a high blue content to supplement it to meet our needs during the day.
This should help us work more safely and efficiently and improve
our concentration for learning. In hospitals and nursing homes,
dynamic lighting will support the sleep/wake cycle and promote
healing processes and a sense of wellbeing. In the evening and
at night, on the other hand, light with a low blue content will help
reduce sick rates, e.g. among shift workers, and lessen sleep
problems generally.
The issue of light and health is a fascinating one. And the discovery of the third photoreceptor gives it a new dynamism: chronobiologists, lighting manufacturers and architects now have the
chance to pool their efforts and substantially improve our quality
of life. licht.wissen 19 is a contribution to this.
.
This booklet provides a practical and user-oriented summary of
what science knows today about the non-visual impact of light
on human beings. It is not a final, authoritative work but an ambitious attempt to describe the nascent, fast-growing field of research examining light, health and efficiency.
Chronobiology will transform our daily lives in the future. One
goal is to strengthen the circadian system by harnessing dy-
Dr. Dieter Kunz, Department of Sleep Medicine, St. Hedwig’s Hospital, Berlin
Institute of Physiology, Charité – Universitätsmedizin Berlin, CBF
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Human evolution is shaped by light
Light is life. The first life on Earth developed three billion years ago with the help of the sun. Homo sapiens – the
“wise” or “knowing” man – has been around for about 170,000 years. For much of that time his sole source of light
was fire. Electric light has been in use for little more than 100 years. No wonder daylight plays such a key role in
human life.
All life on Earth is spatially and temporally
organised. Many processes in nature are
rhythmic. The Earth rotates around its axis
every 24 hours and orbits the sun every
365 days. Hence the sequence of day and
night, summer and winter. The Moon, in
turn, orbits the Earth, joining with the Sun
to create tides and establish a monthly
rhythm.
the course of time, organisms have repeatedly had to adapt their internal clock to external rhythms. The ability to do has proven
a useful evolutionary skill. Even man, for
example, has developed a genetically internalised awareness of the passage of time.
These cycles have had a major impact on
habitats. Many plants, for example, adapt
their survival strategy to day and night.
They open their flowers in response to the
first sunlight, making their nectar accessible
for insects. The insects, timing their foraging accordingly, pollinate the plant – ensuring their own and the plant’s survival. Over
04
[03 – 05] Day or night, summer or winter:
light determines the rhythm of all life on Earth
– including human life. In the course of evolution, human beings have adapted and developed an internal clock.
05
5
Biological rhythms
Controlled by the brain, the same programme is re-run day after day in the human body. An internal clock controls
not only our sleep and waking phases but also our heart rate, blood pressure and mood. Every cell and every organ
has a rhythm of its own that needs to be synchronised regularly with the outside world. Day and night provide the
most important cues.
Many bodily functions are cyclical – both in
human beings and in other living creatures.
Chronobiologists distinguish between three
major categories based on length of cycle:
> Ultradian rhythms span only a few hours.
Examples include times of day and hunger,
sleep and waking phases in infants.
> Circadian rhythms are geared to day and
night. They last around 24 hours (Latin:
circa = approximate, dies = day).
> Infradian rhythms have cycles longer than
24 hours, e.g. the changing seasons.
Circadian rhythm
Human beings and their bodily functions
have daily and seasonal rhythms. From individual cells to entire organs, every unit
controls its own time programme. Breathing
and heartbeat, waking and sleep – all biochemically controlled functions have their
individual highs and lows over the course of
the day.
Shortly before we wake up, our body temperature, blood pressure and pulse rate
rise. Around an hour later, the body produces stimulating hormones. Doctors know
that the risk of heart attack is at its greatest
between 10 a.m. and noon. But this is also
the time of day when we find brain teasers
like Sudoku easiest and when short-term
memory is at its best. So it is a good time
for an exam or job interview.
[06+07] Human beings have internalised
the rhythm of day and night. Sleep and
waking phases alternate with one another
but body temperature, breathing and pulse
also fluctuate according to their own rhythms
– with highs and lows at particular times of
the day.
6
Stomach acid production peaks between
noon and 2 p.m., facilitating digestion of a
midday meal. When producing acid, the
stomach consumes so much energy that
the rest of body feels fatigued.
But even if we skip lunch, we hit a performance “low” at midday. In the early
afternoon, body and mind start to pick up
again. Now, it is sensitivity to pain that
reaches its lowest level. So patients who
are sensitive should make dental appointments at around 3 p.m., not during the
morning.
Anyone engaging in sport between 4 and
5 p.m. gets more benefit than at any other
time of the day. It is the perfect time for
muscle-building and fitness training. And
the glass of beer afterwards is most efficiently digested between 6 and 8 p.m.
When it gets dark, we feel tired. At 3 a.m.,
our body reaches an absolute low. Incidentally, statistics show that this is the time
when the largest number of natural fatalities
occur.
Rhythm is genetically conditioned
Human beings have internalised the rhythm
of day and night. The ability to adjust to the
time of day is anchored in our genetic
makeup. Experiments with test subjects in
isolation chambers have shown that regular
sleep and waking phases are maintained
even if they are not stimulated by daylight.
The genetically programmed rhythm for
human beings is normally slightly more than
24 hours. For some people, the cycle is
shorter than 24 hours; for others, it is considerably longer. On the basis of these differences, people are divided into what are
known as chronotypes.
Chronotypes
Chronotypes are identified mainly by their
sleeping habits. Many people are early
risers – “larks” wide awake at the crack of
dawn. But there are also “owls”, who need
more time to face the new day. Their internal clock runs significantly slower than that
of other people. Conversely, the internal
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07
7
clock of a lark runs too fast. Its cycle may
be complete within 23 hours, while that of
an owl may be as long as 26 hours.
Compared to the average, both groups
have a displaced sleep/wake rhythm. Larks
are urged by their internal clock to get up
early, owls are turned into a morning
grouch. The latter group, in particular, experience a kind of permanent “social jetlag”
if they are wrenched from sleep early in the
morning, long before they have a subjective
sense of having slept enough. Despite external cues as work-times or daylight, they
find it difficult to adapt to the shorter rhythm
of the Earth’s rotation. Each new day adds
to their sleep deficit, which has to be made
up at weekends.
But early risers also find their internal clock
annoying – especially at the weekend when
they go to bed late but still wake up early in
the morning as usual. Extreme chronotypes
often suffer from permanent conflict with
their biological clock. They are more prone
to organic illnesses and statistically more
likely to resort to nicotine and alcohol.
Seasonal differences
Our chronobiological rhythms are also influenced by summer and winter. In the dark
months of the year, we tend to be less fit,
we have difficulties concentrating and our
responses are slower. We also eat more,
so our body weight increases and bloodsugar levels rise.
The seasons also have a psychological
impact. Especially in places with distinct
seasons, people are tenser in winter than
in summer and also generally more badtempered.
However, some people do not just get into
a bit of a low mood in winter; they become
clinically depressed. They suffer from seasonal affective disorder (SAD). In Germany,
one in ten adults is affected (see page 20,
Light therapy against SAD symptoms).
Rhythm and age
Young parents are often stressed and tired,
and that may well be due to the internal
clock of their child. Infants and toddlers are
8
still governed by ultradian rhythms, i.e.
phases of three or four hours’ duration.
They do not adapt to day and night until the
age of five.
But as soon as youngsters reach their
teens, new rhythms develop – rhythms that
at best baffle their parents. A teenager will
go to bed late and sleep longer in the
morning, often for more than eight hours.
At the age of 18 to 20, sleep requirements
then decrease to between seven and eight
hours. From the age of 30 onwards, the
quality of sleep steadily declines. We sleep
less deeply and feel less refreshed, even
though we go to bed earlier and at more
regular times.
At the age of 70, the symptoms become
more acute: our body requires less and less
sleep at night and body temperature virtually stops fluctuating over the course of the
day. Our sleep/wake rhythm gets increasingly out of sync with external rhythms. This
is why elderly relatives nap in the afternoon.
The older we are, the less our body distinguishes between day and night.
08
[08] Sleep/wake rhythms change over the
course of our life.
09
[09] Human performance curve over the
day: body and mind are fittest around 10 a.m.
At 3 a.m., they reach a low.
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Our internal clock
Every human being ticks at a different rate. But we all respond to day and night. Each cell has its own internal
clock and its own rhythm in the “concert” of the human body. However, it is blind to the outside world. For all of the
peripheral clocks involved in biological processes, central control and synchronisation with the environment are
provided by a “master clock”. It takes its cue from light.
SCN: the master clock
The role of mediator between light and
the body’s response to it is played by the
suprachiasmatic nucleus (SCN). Its main
function is to coordinate the many tiny
clocks in the body that have no direct link
to the outside world. Metabolism needs to
be adapted to the time of day. It is the only
way the many different processes can be
synchronised.
The SCN acts as a master clock for cell
activity by using synapses and neurotransmitters to synchronise the various clocks
in the body. It does this by switching them
on or off, activating or inhibiting enzymes,
regulating the production or prevention of
hormones.
The SCN consists of two brain nuclei the
size of a grain of rice. Located above where
the two optic nerves cross, they are the
control centre of our internal clock. Each
one is comprised of thousands of nerve
cells whose circadian rhythms are “set”
daily by daylight.
Third photoreceptor
[10] Human beings regularly synchronise
their internal clock with the outside world.
The natural pacemaker is daylight.
[11] It was not until 2002 that scientists
discovered special ganglion cells in the retina
that do not have a visual function. They are
most sensitive in the nasal and lower part of
the retina. Rods and cones are responsible
for vision.
to the brain. Altogether, science has identified 20 different types. In the new type,
which forms the third receptor, researchers
discovered melanopsin, a light-sensitive
protein originally found in the skin of frogs.
Its purpose there is to change the colour of
the frog’s skin to blend with the surroundings.
In experiments, light-insensitive cells in
mice were transformed into light-sensitive
ones after being injected with human
melanopsin. Their response was most sensitive to the blue light of the visible spectrum at wavelengths around 460 nanometres.
The first evidence of the new photoreceptor
in humans was indirect. It was acquired by
scientists irradiating test subjects for an
hour and a half at night with monochromatic light of different wavelengths and observing the level of melatonin (sleep hormone) in their blood. They compared the
values before and after irradiation and
found that blue light suppresses melatonin
production at night.
Light acts as pacemaker for our
internal clock
The fact that even late risers eventually
wake up without an alarm clock is due to
their circadian rhythm, which is stimulated
by light. For a long time, it was not known
how the relevant light stimuli are perceived.
But in 2002 scientists discovered a third
photoreceptor in the retina. Unlike the rods
and cones, however, its function is not visual. It is a special ganglion cell, distributed
over the entire retina.
So the crucial cues for the SCN are provided by light. But melanopsin-containing
ganglion cells do not process light stimuli
visually: they send signals through the
retinohypothalamic tract, which connects
them directly with the SCN, the pineal gland
and the hypothalamus, which is probably
the most important control centre of the autonomic nervous system.
Ganglion cells form a layer of nerve cells
facing the vitreous body of the eye and act
as output neurons, transmitting visual information via the optic nerve from the retina
In the evening, the pineal gland secretes
melatonin, which makes us feel tired. In the
morning, the level of melatonin in the blood
then ebbs. The first sunlight promotes this
11
Visual (green) and biological (blue) path
visual centre
suprachiasmatic
nucleus (SCN)
pineal gland
superior cervical
ganglion
retinohypothalamic
tract
spinal cord
12
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genetically conditioned rhythm by additionally inhibiting the hormone’s production.
Hormones: the internal clock’s
messengers
Digestion, mood, sleep – human beings
are governed by complex biochemical
processes. Hormones regulate when food
is easily digested, when performance peaks
and when sleep is at its deepest. Circadian
rhythms are determined particularly by
melatonin and cortisol because they impact
on the body in opposite cycles. Serotonin –
a natural anti-depressant – also plays a vital
role in this biochemical process.
Melatonin
Melatonin makes us feel drowsy, slows
down bodily functions and lowers activity
levels to facilitate a good night’s sleep. It
also ensures that a large number of metabolic processes are wound down. Body
temperature falls; the organism, as it were,
is put on the back burner. In this phase,
the body secretes growth hormones that
repair cells at night.
Cortisol
Cortisol is a stress hormone, produced
from around 3 a.m. onwards in the adrenal
cortex. It stimulates metabolism again and
programmes the body for day-time operation. The first light of the day then stimulates the third receptor in the eye and suppresses the production of melatonin in the
pineal gland. At the same time, the pituitary
gland makes sure the body secretes more
serotonin.
[12] Rods and cones transmit the visual
information to the visual centre of the brain
via the optic nerve (green path). The ganglion
cells, on the other hand, are connected with
the superior cervical ganglion in the spinal
cord and with the SCN by the retinohypothalamic tract (blue path). The SCN uses
pineal gland and hormone balance to synchronise the body with the outside world.
[13] Cortisol and melatonin run opposite
to one another: the body produces cortisol in
the morning. The concentration of it in the
blood peaks at around 9 a.m. and then
steadily declines during the day. Melatonin
production starts at night, reaching a peak at
around 3 a.m.
Serotonin
Serotonin acts as a mood-enhancing,
motivating messenger. While the level of
cortisol in the blood falls during the day in
a counter-cycle to melatonin, serotonin
helps us achieve a number of performance
peaks. When daylight fades, the internal
clock switches to night.
tired during the day and lack energy and
motivation. Insufficient exposure to stimulating light during autumn and winter can
turn the process into a downward spiral.
At that time of year, some people develop
seasonal affective disorder (SAD). Their
internal clock misses its cues because the
hormonal balance in the brain is upset.
Biological darkness
21st century man leads a life that is more
and more divorced from natural rhythms.
Many people work shifts or in windowless
buildings. In the morning or evening, at the
supermarket or office, artificial lighting is
almost invariably present, enabling us to
see or simply turning night into day.
But even where lighting is fully compliant
with standards, the dynamism and biological effects of daylight are missing. Scientists describe the situation as “biological
darkness”, which impacts on human beings
by disrupting their internal clock.
Artificial lighting supplementing daylight
The purpose of biologically effective artificial lighting is to enhance the impact of daylight indoors. During the course of the day,
changes occur in the angle of incidence,
direct and indirect lighting components,
light colour and brightness. So modern
lighting systems provide dynamic light of
different colour temperatures and different
illuminance levels.
Artificial lighting can thus stabilise human
rhythms and synchronise them with periods
that deviate from our internal clock. Crucially important here is the point in time at
which the eye is exposed to bright light.
Light in the evening delays melatonin production and puts back our internal clock.
Light early in the morning, however, brings
natural rhythms forward.
However, if our body does not get enough
light during the day, it produces only a low
level of melatonin. As a result, we sleep
badly, we wake feeling unrested, we are
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Biologically effective light
Light helps regulate the biological processes in the human body. It synchronises them with the environment.
But light is not always available in sufficient quantity. Fortunately, it can be supplemented by biologically effective
artificial light.
Outdoors, at home or at work – light is
essential for human life. Too little light can
cause a delayed reaction in our internal
clock or make sleep/wake phases less pronounced. In both instances, the effect on
chronobiological rhythm is negative and
can cause health problems.
Combining daylight and artificial light
The brightness of daylight varies considerably, depending on geographical position,
weather, season and time of day. In Central
Europe, most interiors could be illuminated
with natural light from around 8 a.m. through
to 5 p.m. In the majority of cases, however,
the daylight admitted by windows does not
reach deep into the room.
In these cases, biologically effective lighting
can either be activated in addition to daylight or steplessly regulated to compensate
automatically for changes in daylight. So
daylight and artificial lighting should be
used to complement one another – and not
compete – as sources of interior lighting.
What is more, combining the two saves
energy and enhances lighting quality.
illuminance and colour temperature of daylight change dynamically from sunrise to
sunset.
Parameters of biologically effective light
Nature defines the parameters for biologically effective light:
> illuminance
> planarity
> direction of light
> colour temperature
> dynamism.
Daylight intensity reaches thousands of
lux. However, studies show that even illuminances between 500 and 1,500 lux are
biologically effective. To achieve this,
though, the light needs to reach lots of
receptors in the retina. So it has to come
from a planar light source like the sky and
enter the eye from above and from the
front. Colour temperature also plays a crucial role: it should be similar to daylight,
which has a spectrum that contains biologically effective blue light and is found
agreeable by human beings. Finally, the
Artificial lighting that is designed according
to these parameters effectively and efficiently supports the positive effects of daylight on the human organism.
[14] Light energises and influences our
mood.
[15] Colour temperature determines the
way we are affected by light: a warm white
spectrum is relaxing, daylight white invigorating.
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Biologically effective light indoors
To be biologically effective indoors, artificial lighting takes a leaf from nature’s book: intelligently controlled,
it supplements available daylight and provides the eye with the illuminance required at the different times of day.
Modern lamps ensure the right spectrum, luminaires the right distribution of light.
Dynamic lighting control
Biologically effective artificial lighting should
be geared to the circadian rhythms of the
user. It needs to support the biological
processes that define active and rest
phases. During the course of the day, the
position of the sun and the colour temperature of natural light change. Dynamic lighting takes account of those changes and is
increasingly replacing static lighting solutions for indoor applications.
This is possible thanks to intelligent control
and sensor technology. Luminaires that
radiate direct and indirect light simultaneously, for example, can be fitted with separately controllable light sources of different
light colours. Governed by a lighting management system, they can thus deliver
light with a changing colour temperature
designed to support our natural biological
rhythms.
Natural light distribution
The distribution and spectral sensitivity of
the third type of receptor in the retina
show how perfectly the eye has adapted to
natural conditions: the most sensitive
melanopsin-containing ganglion cells are
located in the nasal and lower part of the
eye (see p.10). This is because light from
the sky enters the eye from above and from
the front. To be biologically effective, an
artificial lighting system needs to direct light
in the same way.
The effect is also achieved where room
surfaces such as the upper part of a wall
and ceiling have a light-coloured finish and
are used to bounce light back into the
room. Luminaires that radiate both direct
and indirect light or wall and ceiling washers that provide only indirect lighting are
particularly suitable for this.
Natural light spectrum
Electromagnetic radiation in the wavelength range between 100 nanometres and
1 millimetre is referred to as optical radiation. Light is the radiation visible to the
human eye in the 380–780 nm range.
Optical stimuli are registered in the human
eye by three different cones which respond
sensitively to red, green or blue radiation.
But we do not perceive colours as equally
bright. Experiments with test subjects have
shown that colours in the yellow-green
spectrum at 555 nm are perceived as the
brightest. (see Fig.19, p. 19, v(␭) curve).
Bold reds and blues, on the other hand,
tend to appear dark.
Cones are not the only receptors in the eye
that contribute to the visual process. There
are also rod cells, which enable us to see in
dim light. They cannot distinguish colours,
however. Their brightness sensitivity is
shown by the curve v’(␭). The biologically
effective range is the blue spectrum around
460 nm (curve c(␭)).
Tailored spectrum
[16] Large-surface luminaires direct light
to the eye in a biologically effective manner
from above and from the front. The effect is
enhanced where ceilings and upper walls
are bright and reflective.
16
Studies have shown that the receptors can
reach a state of saturation. So to achieve a
circadian effect, it is not enough to use a
punctual light source delivering high blue
content light. As many receptors as possible need to be addressed, so large area luminaires are an answer.
At the time the third type of photoreceptor
was discovered, only fluorescent lamps
could be made to deliver light with a higher
blue content. Today, lamp and luminaire
manufacturers can engineer lots of other
light sources for optimum biological effect.
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17
Light emitting diodes (LEDs) are particularly
flexible. The spectrum of white LEDs consists of blue light produced in the semiconductor and broadband yellow-green light
produced in the luminescent material. Blue
and yellow components can be varied almost infinitely. It is thus possible to produce
light with a spectrum tailored for biological
effect.
Yellow LEDs have only a minimal effect,
however, and red LEDs nearly no effect
whatsoever. So manufacturers have come
up with hybrid luminaires, which combine
warm white fluorescent lamps with blue
LEDs or daylight white models with yellow
and red LEDs. These solutions enable bio-
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logical and visual effect to be balanced and
varied as required.
Not all lamps should be biologically
effective
Due to production reasons, some light
sources emit what is known as a mercury
line. This can be seen as a clear spike at
434 nm in the spectrum of the three-band
fluorescent lamp shown in Fig. 20. It is
found in the spectral range to which the
third type of photoreceptor in the eye is
most sensitive. But the circadian spectrum
is not required at all times of day. So lamp
and luminaire manufacturers involved in the
PLACAR joint research project have devel-
18
oped fluorescent lamps that eliminate or
emphasize the circadian wavelength range
and still meet all visual quality standards.
Illuminance varies dynamically
lighting was found to help stabilise the
sleep/wake rhythm of elderly residents.
They also became more communicative. In
the schools project, students performed
better and were more attentive and focused.
During the course of a day, dynamic lighting not only varies its colour temperature
from warm white to daylight white; it also
adapts its 500–1,500 lux illuminance to the
human circadian rhythm by supplementing
natural optical stimuli as required. This is
particularly recommended for rooms where
people spend a good length of time. The
positive effects have been shown by pilot
projects in retirement homes (see p. 34)
and schools (see p. 32). In the former case,
[17+18] The ganglion cells of the third photoreceptor are most sensitive in the nasal and
lower area of the retina. This is evidence of
the eye adapting to natural conditions, because light from the sky enters the eye from
the front and above. The most biologically effective light, therefore, is light that enters the
eye from this direction.
[19] Action spectrum of melatonin suppression [c(␭)] compared to the brightness sensitivity of the eye at night [v’(␭)] and during the
day [v(␭)]: the most biologically effective light
is in the 460 – 480 nm wavelength range.
[20] PLACAR fluorescent lamp with a
colour temperature of 10,000 Kelvin
19
PLACAR research project
100% –
rel. intensity
75% –
50% –
25% –
0% –
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400
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450
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500
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550
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600
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700
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750
The PLACAR research project was launched in 2006
to examine the effect of different lamps on different
elements of the circadian system. The acronym stands
for “Plasma Lamps for Circadian Rhythms”. The longrange research results are intended to lead to the
development of lamps which have a positive effect on
circadian rhythms. Those involved in PLACAR include
German lamp and luminaire manufacturers, the
Psychiatric and Psychotherapy Clinic of the Berlin
Charité Hospital and the Leibniz Institute of Plasma
Research and Technology at Greifswald.
wavelength (nm)
20
19
Light therapy
Biologically effective light is also used in medicine. Seasonal affective
disorder (SAD), a mood disorder that occurs in the darker months of the
year, can be successfully treated with light. Early studies now suggest
that light therapy is also effective against non-seasonal depression and
other ailments.
Trees lose their leaves, storks fly south,
hedgehogs hibernate. Only human beings
think they can defy the seasons. Clearly, a
life ruled by nature does not fit easily into
the industrialised world. No employer would
accept employees working to a schedule
determined by biorhythms. Consequently,
many people struggle through autumn and
winter in noticeably low spirits.
Seasonal affective disorder (SAD)
Lack of light is indeed a serious problem:
if insufficient natural light is available,
5 – 20 % of all people develop veritable
“deficiency symptoms”. Symptoms such
as greater need for sleep, lack of energy,
mood swings and even depression can
develop during winter months into SAD,
a condition that needs to be treated.
US scientists have been studying this
phenomenon since the early 1980s. What
distinguishes SAD from other forms of
depression is mainly the fact that symptoms subside as the days grow longer in
spring but then return again in autumn.
Ravenous appetite from lack of light
[21] At the doctor’s, in hospital or at home:
light therapy is an effective and straightforward safeguard against seasonal affective
disorder.
20
In contrast to other depressive patients,
people affected by SAD do not suffer from
insomnia. On the contrary, they go to bed
earlier. Yet they still have difficulties getting
up. Nor do they lose their appetite, which
is a typical symptom of depression. They
may actually develop cravings, especially
for carbohydrates such as chocolate, potato products or bread. So scientists believe there may be several causes for SAD:
malfunctioning photoreceptors on the retina
might be one of them, an insufficiently
pronounced sleep/wake rhythm could be
another.
21
21
One probable factor is that SAD patients
are less able to adapt to the shorter days
of winter. This throws their internal clock
out of kilter. Lack of available light in absolute terms is also discussed as a contributory factor. Supporters of this theory point
to the fact that SAD affects one in three
adults in Alaska but only one in 25 in
Florida.
However a comparative representative survey by leading chronobiologists in the US
and Switzerland leads to a different conclusion. The researchers found that in 1999
a significantly larger percentage of Americans suffered from a milder form of SAD
than Swiss – despite comparable weather.
So the study shows that SAD is not dependent on hours of sunshine but on personal exposure to light. To keep our internal flywheel turning, it is advisable to spend
a sufficient amount of time outdoors even
in winter.
Daylight spectrum therapy devices
For people who do not get enough daylight
during the day, light therapy devices are a
genuine alternative. Smaller devices are
also available for home or office use. What
distinguishes them from the professional
equipment used in hospitals or doctors’
surgeries is mainly the size of the luminous
surface. Hospital devices are the largest.
They can be used to treat three to four patients simultaneously. Devices for the
home, however, are designed only for one
person.
The lamps are monitored by an operating
hours counter. After 8,000 operating hours,
their luminous flux is around 20 percent
reduced and they should be replaced. The
beam angle of a light therapy device is
specially designed to take account of the
geometry of the eye. Melanopsin-containing ganglion cells (see p.10) are widely distributed over the retina and most sensitive
in the lower part of it. The more receptors
are addressed, the more successful the
treatment.
Another factor to consider is that human
pupils open to different degrees. So the
same luminance does not necessarily result in the same irradiation of the retina.
22
Finally, the lens of the human eye becomes
more and more opaque with age, letting
less light through. Therapy devices thus
need to be sufficiently bright.
Technical requirements for light
therapy devices
Therapeutic light sources should have a
luminance of around 8,000 candela per
square metre (cd/m2). Luminance is the
measure of brightness of a luminous or illuminated surface as perceived by the
human eye. Research has shown that it
should not exceed 10,000 cd/m2.
The luminous face of a therapy device
should be as large as possible. The brightness needs to be spread as evenly as possible over the luminous surface.
Therapy devices radiate light in a wide
beam so that the patient can move around
in front of the luminaire within a relatively
large area. Depending on distance from the
device, illuminance can be as much as
10,000 lux. Light is considered therapeutically effective from 2,000 lux upwards. The
colour temperature – around 6,500 Kelvin –
corresponds to that of daylight at noon.
The rays are particularly intensive in the
short-wave blue region of the visible spectrum. Special glass filters cut out all harmful ultraviolet light. Light therapy devices
cannot and should not tan the skin.
Light therapy suppresses sleep
hormone
As far as doctors know today, light therapy
works exclusively via the eye. When daylight falls on the retina, the pituitary gland in
the brain produces hormones and neurotransmitters such as serotonin.
motivation. To enable the body to step up
the secretion of serotonin, light therapy
lamps simulate the intensity and colour
temperature of daylight. What is more, they
produce short-wave light in the blue region
of the visible spectrum, which stimulates
the ganglion cells of the third photoreceptor in the retina. These then inhibit the
production of the hormone melatonin. As a
result, we are alert and productive during
the day and sleep better at night. Melatonin thus stabilises our circadian rhythm.
The artificial lighting normally found at a
workplace is not usually enough to achieve
this effect.
Light in the morning is the most effective
Light therapy is best administered in the
morning. It tells our biological clock that the
day has begun and that bodily functions
need to be activated. Conversely, it is not a
good idea to apply light therapy in the
evening because it will cause melatonin
production to be suppressed and make it
harder to fall asleep.
The frequency and length of therapy sessions required vary. The regime is prescribed by the doctor in consultation with
the patient and depends on the severity of
the symptoms. In most cases, a beneficial
effect is noted within one to two weeks.
Light therapy is also an effective preventive
measure for patients who suffer regularly
from SAD. There are no known serious
side-effects. Occasional complaints such
as eye irritations, headaches and dry skin
clear up after a few hours. As a general
rule, however, anyone considering light
therapy should first have a word with an
ophthalmologist because caution is advised in the case of certain eye disorders.
Great potential of light therapy
Low levels of serotonin are a frequent
cause of depression because it works as
a messenger substance transmitting information between brain cells. Vital functions
and thought processes work only when
enough of it is present. And whether they
work or not impacts on our mental state.
Serotonin brightens our mood, increases
our sense of wellbeing and boosts our
Light therapy has recently been used to
cure a variety of ills. There are even reports
of Parkinson’s and Alzheimer’s patients
being irradiated with biologically effective
light, although there is currently no clear
scientific evidence of therapeutic efficacy.
What early studies do show, however, is
that light therapy can be successfully used
to treat premenstrual complaints, for exam-
ple, especially the attendant emotional
symptoms.
There are also indications that light therapy can help those with bulimic eating disorders, especially seasonal bulimia. A
comparative study conducted by the naturopathy department of Blankenstein Hospital in Hattingen shows that light therapy
produces good results even in cases of
non-seasonal depression, especially in
combination with St. John’s wort.
Doctors are only slowly beginning to
understand the therapeutic effects of light.
The first signs are promising. But one
thing is certain already: light therapy is a
natural anti-depressant against the “winter
blues”, as the milder form of SAD is also
known.
22
> 2,000
23
> 4,000
> 6,000 > 8,000
> 10,000 > 12,000 > 14,000 > 16,000
100% –
rel. intensity
75% –
[22]
Light therapy device for home use
25% –
[23] Luminance distribution of a light therapy device with 26 mm diameter fluorescent
lamps
[24] Spectrum of a light therapy device
(special daylight white fluorescent lamps): the
light colour resembles daylight.
50% –
0% –
|
|
|
|
|
|
|
|
400
450
500
550
600
650
700
750
wavelength (nm)
24
23
25
26
27
Lighting design
Daylight changes – so do professional lighting concepts. Today they are able to harness the biological impact
of daylight indoors. To ensure that lighting really is biologically effective – and provides comfortable visual conditions
at the same time – lighting designers need to pay attention to a number of factors.
Quality features
Light colour is crucial
Good lighting helps us perform our daily
tasks. So biologically effective lighting
needs to meet all visual quality requirements. At a desk, at a machine or in an
operating theatre, lighting needs to provide
optimal work area illumination without
impairing vision.
The different colour temperatures of fluorescent lamps depend on the mix of phosphors
in the tube. These have different spectral
distributions, which impact differently on the
human circadian system. Light with a higher
blue content, for example, is more circadian-effective than warm white light.
A good lighting installation tailors illuminance to the visual task and distributes
luminance evenly in the room. It limits
direct and reflected glare and has good
colour rending properties. The light it delivers does not flicker and takes account of
incident daylight.
Spatial distribution of light
The basic requirements are set out in the
standard DIN EN 12464-1 “Light and
lighting – Lighting of work places”. This
stipulates minimum values for the relevant
lighting variables and defines minimum
requirements for good lighting quality.
A lighting installation for biologically effective lighting also needs to ensure that light
colour and direction of light are right for the
conditions.
Light colour is expressed as a colour temperature in Kelvin. It indicates the intrinsic
colour of the light emitted by a lamp. The
colour temperature of the sky varies mostly
between 6,000 and 10,000 Kelvin.
24
Light colour is not the only variable important for biologically effective lighting. Our
eyes need to be able to perceive bright
areas in the room as effectively as possible. This is achieved by using large-area
luminaires to brighten the space. Alternatively, luminaires with indirect beams can
be used to illuminate the ceiling and the
upper third of the walls.
The activating effect of light is normally
required only during the day. Warm light
colours should be selected in the evening.
The visible brightness in the upper part of
the room can then also be reduced.
For dynamic lighting, care needs to be taken
to ensure that the spectrum of the light radiated by the lamp is not negatively influenced
by the ambient colours in the room.
28
29
30
[25 – 30] Dynamic lighting in the office:
settings for biologically activating lighting are
used during the day only if activation is required.
[31+32] Darklight technology: the light is
distributed to cater for visual tasks at the
desks.
31
32
33
34
Material characteristics and
light colour
Lamp light is altered in luminaires, especially by optical control elements such as
louvers, enclosures or prisms. This may
result in the light that reaches the eye having a different spectral composition than
that radiated by the lamp. The spectral
properties of optical control elements
determine the quality of dynamic lighting.
Where components are exposed for long
times at high temperatures to light with a
greater blue content, consideration also
needs to be given to their ageing resistance. In the common case of LEDs with
plastic lens systems, transmission proper-
[33+34] Optimised lighting solution: biologically effective luminaires (33) radiate light over
a large area in direct and indirect beams,
using luminaire elements or the ceiling and
upper part of the walls as bright reflective
surfaces (34).
ties in the blue spectral region need to be
maintained over the entire life of the light
source.
Room environment and light colour
The impression a room makes is significantly influenced not only by the light
colour of the lamps but also by the colours
of the furniture, walls and ceiling. Dark
colours reflect less light than light ones. A
great deal of light can be “lost” here, especially where light is cast exclusively onto
room surfaces by indirect luminaires. Wood
finishes or reds and browns actually absorb the blue content of the spectrum and
thus considerably reduce the biological
effect of the lighting.
25
Lighting quality and energy efficiency
Lighting should be designed to meet human needs – today and in the future. To enable all the advantages
of artificial lighting to be carried forward into the future, lighting also needs to be environmentally sound.
Lighting quality and energy efficiency are not conflicting attributes.
Light enables us to get bearings. It assists
us in our work, creates atmosphere and
can even impact positively on our health.
So it is not surprising that we want optimal
lighting for as many situations in life as
possible. Energy-saving lighting solutions
meet this need while making responsible
use of resources.
According to the International Energy
Agency (IEA), 19 percent of global energy
consumption is used for lighting. So intelligent use of light can make a big contribution to energy efficiency.
Particularly energy-efficient lighting solutions address the task in a variety of ways.
To illuminate space with different lighting
needs, a lighting concept needs to incorporate a number of components. Luminaires and light sources should also have
a high power efficiency rating and the light
should be dimmable. What is more, modern lamps have an extremely long life.
Finally, the greatest potential for savings
is offered by intelligent lighting control.
Lighting that is governed by a daylight dependent control system consumes up to
35 percent less energy than a conventional, non-consumption-optimised lighting
solution. Timers and presence sensors cut
consumption even more.
Ergonomic factors
The quality of a lighting system is determined by a number of ergonomic factors:
> visual performance
> appearance
> visual comfort
> vitality
> individuality.
[35] Interiors where daylight is utilised are
ideal. Intelligent management regulates artificial lighting to supplement the daylight as required. This saves energy and costs.
26
Conserving energy resources
Lighting quality needs to be viewed in the
context of energy efficiency. The German
Energy Conservation Ordinance (EnEV) sets
out minimum efficiency requirements for the
operating energy consumption of lighting
installations. The criteria and boundary conditions of use defined in DIN V 18599 enable the energy consumption of rooms and
buildings to be rated.
Where a lighting concept meets both quality requirements, there is no conflict between economic and environmental aspects. However, application of the EnEV
must not result in lighting quality being neglected.
Intelligent lighting control is the
most efficient
In a research project at the Fraunhofer Institute for Building Physics at Holzkirchen
near Munich, scientists are studying different building service systems – e.g. heating,
cooling, ventilation and lighting systems –
under realistic conditions in rooms with natural and artificial lighting.
As far as lighting is concerned, the most efficient option available is daylight-controlled
direct/indirect working area lighting that
also illuminates the walls. In the morning
and late afternoon, the end walls of the
room are additionally illuminated to provide
higher vertical illuminance for better visual
and emotional impact and visual comfort. A
wallwasher with a colour temperature of
6,500 Kelvin mounted on the rear wall significantly reduces afternoon fatigue.
Measurement results show that the lighting
installation described above merits a “very
good” rating. Even if the connected load
is high, energy consumption is on a par
with standard lighting – and the ergonom-
35
ics are very good. The best balance between lighting quality and energy efficiency
is displayed by installations with a high
degree of automation. Daylight control and
calculated activation and deactivation of
lighting components significantly reduce
energy consumption.
Accent lighting is attractive and
motivating
The “Licht und Mensch” study conducted
by the Lüdenscheid-based German institute of applied lighting technology DIAL
looked at how room users assess different
light distribution patterns in a room. Here,
too, it was found that additional wallwashing results in a room being perceived as
brighter. What is more, where supplementary accent lighting is used, the visual appeal of the room is enhanced. Test subjects classed the lighting situation here as
“inviting, vibrant, cheerful or interesting”.
Purely direct and purely indirect lighting
was rated negatively. Accentuated wall surfaces, on the other hand, engendered a
greater sense of wellbeing.
In one of the most comprehensive studies
of its kind, researchers working for the
Light Right Consortium in New York also
concluded that good lighting improves productivity. 9–31 percent of persons whose
workplace was illuminated only by direct
lighting systems judged this to be disagreeable. However, 91 percent of test
subjects found a system that comprised
both direct and indirect lighting as well as
wallwashers to be agreeable. Where the
workplace lighting was also individually
dimmable, employees were found to be
more motivated, persevering and alert. The
work they performed was also more accurate and thorough.
In view of these findings, lighting quality and
energy efficiency cannot be played off
against one another. Intelligently controlled,
dynamic lighting impacts positively on
human beings. The slightly higher energy
consumption it entails in comparison to
standard lighting is compensated by enhanced motivation, performance and
health.
27
36
37
28
38
Practical example:
Dynamic office lighting
Illuminance, drive and performance at work are more closely connected than they appear at first glance.
Correct lighting not only makes office workers more alert; it also motivates and boosts efficiency.
That is the finding of a current study looking at the impacts of dynamic lighting on
employees in an office environment. At the
heart of the study, 19 people in an openplan office performed four-week work stints
in different lighting atmospheres. The researchers then compared the subjective
and measurable effects with the results of
a control lighting set-up.
white light sources and the indirect luminaires with 8,000 Kelvin cold white models.
For most of the day, they run at 500 lux
and 3,000 Kelvin. But when human performance slumps in the early afternoon,
the illuminance surges to as much as
1,000 lux. Between 1.15 and 2.45 p.m.,
the colour temperature also rises – to
around 8,000 Kelvin – and the warm white
component of the light is reduced.
Different lighting atmospheres
The key to correct lighting is in the mix
For the ceiling lighting, elements were
selected from three individual luminaires
designed to provide both direct and indirect lighting. Lighting atmosphere 1 basically corresponds to the control lighting
with standard-compliant 500 lux illuminance and a colour temperature of 4,000
Kelvin. The only difference is that the direction of light changes dynamically during the
course of the day. Like sunlight, the light
radiated by the system is direct in the
morning, becomes more diffuse towards
midday and then increasingly direct again
in the afternoon.
In lighting atmosphere 2, the direct luminaires are fitted with 3,000 Kelvin warm
[36] Dynamic colour temperature and
illuminance: biologically effective light also
boosts human performance in the office. It
activates, motivates and creates atmosphere.
[37] In the early afternoon, cold white light
mobilises reserves: it energises, promotes
concentration and thus helps bridge the
phase of sleepiness after lunch.
[38] In the late afternoon, warm colour
temperatures make for a gentle transition to
leisure at the end of the working day.
The test subjects performed their normal
work during the field trials. Each morning,
they filled in a sleep report designed to
show how refreshed they were on their arrival at work. The scientists then conducted
response tests to identify degrees of alertness during the day. In addition, the participants completed subjective questionnaires
about sense of wellbeing, brightness, direction of light and light colour.
The findings show that a balanced mix of
daylight white indirect lighting and warm
white direct lighting makes employees more
alert and more efficient. Higher illuminance
and colour temperatures at certain points
impact positively on response times – and
not only at noon but continuously throughout the day. Those who took part in the
study felt better and more alert as a whole.
ing. Invigorating in the morning, boosting
concentration in the afternoon, promoting a
gentle transition from work to leisure at the
end of the day – an electronic control system steers the lighting through predefined
lighting atmospheres that positively support
human circadian rhythms. The large-area
luminaires are fitted with daylight white and
warm white fluorescent lamps. Infinitely adjustable, they can produce light of any
colour temperature between 3,000 and 500
Kelvin at different illuminance levels.
The lighting at individual workplaces can
also be tailored to personal physiological
requirements and the lighting in conference
rooms can be adjusted to create the right
lighting atmosphere for meetings or presentations.
The energy requirement of a complete solution like this is around 25 percent greater
than that of a non-regulated, fixed-colour
lighting installation with electronic ballasts.
The acquisition cost is around 20 percent
higher. Because employees are more focused and motivated, however, productivity
in Hamburg has increased by the same
amount.
A third lighting atmosphere showed that
participants found warm light colours significantly more agreeable in the morning and
evening.
Good lighting makes us more productive
The research findings have been taken up
in a ground-breaking lighting project in
Hamburg, where a company has fitted an
entire office building with fully dynamic light-
29
Practical example:
Dynamic industrial workplace lighting
At machines or in assembly lines, industrial workers are more alert and more focused if they have the right light.
It reduces errors, heightens safety and boosts productivity.
A study in Finland shows that if manual
production workers had the choice, they
would select significantly higher illuminances than are required by law. The finding stems from a field experiment in a factory where electrical components were
previously assembled under lighting delivering 500 lux static illuminance. That is the
value stipulated for moderately difficult assembly work in DIN EN 12464-1 “Light and
lighting – Lighting of indoor work places”.
More than just seeing
For the experiment, the scientists installed
a lighting system that permitted infinite individual regulation up to 3,000 lux at each
workplace. And what they found over the
next 15 months was that 48 of the 49 assembly workers chose significantly higher
illuminances – even though the original
500 lux was a good level of illuminance for
the visual task.
So the reason that employees choose
brighter light needs to be attributed partly
to non-visual effects. The illuminance levels
selected were biologically effective: they not
only facilitated the visual task but also enhanced concentration, performance and
sense of wellbeing.
These findings are supported by a second
study, in which workplace lighting in another assembly shop was switched back
and forth between two different settings.
The lighting in this experiment consisted of
ordinary continuous rows wired to permit
an optional 800 or 1,200 lux illuminance.
Over a period of 14 months, the illuminance
was re-set between shifts on an irregular
basis.
Results analysis showed that when the
light was brighter, the average assembly
30
time for the same product was 7.7 percent
shorter.
Cost-efficient route to greater safety
Dynamic lighting also supports human circadian rhythms at industrial workplaces.
An activating factor in the morning and at
midday, it can sustainably heighten alertness and productivity.
In industrial halls with window walls or skylights, artificial lighting can be flexibly regulated to supplement daylight. This saves
energy and costs. Realising such a system
calls for electronically controllable luminaire
systems delivering a combination of warm
white and daylight white light. They are
recommended for office-like production
areas and small halls with a high density of
employees.
Alternatively, existing lighting systems can
be retrofitted with cooler colour temperature lamps of 6,500 Kelvin or higher. When
lamps are replaced, however, care needs
be taken to ensure that the maintained illuminance is still standard-compliant. The
financial outlay is lower here but the light is
still biologically effective. This boosts productivity and motivation. Above all, however, it heightens concentration and thus
makes for a safer industrial workplace. So
it also helps avoid serious accidents.
[39] Daylight makes for safer and more
productive work in an industrial manufacturing facility. It can be supplemented or replaced by biologically effective lighting.
39
31
40
Practical example:
Dynamic school lighting
Light creates moods. It stimulates or soothes. Recently, the lighting industry and researchers installed lighting
with these properties in schools in an experiment investigating the impacts of dynamic lighting on learning.
The findings are astonishing.
The study was carried out at three schools
in Hamburg, where classrooms were fitted
with dynamic lighting. Conducted by the
epidemiology and evaluation working
group of the Department of Child and Adolescent Psychosomatics at HamburgEppendorf University Hospital, the study
ran from October 2007 to the start of the
2008 school summer vacation.
Light for bright minds
Week by week, the scientists reviewed the
impacts of predefined lighting programmes
32
on concentration and learning outcomes.
The data of the group learning under dynamic lighting (intervention group) were
compared with the results of a control
group performing the same tasks, concentration exercises and text comprehension
tests under standard lighting.
A set of three lighting programmes proved
highly effective. Lighting programme 1 was
designed to “activate” the students in the
morning at the beginning of the first lesson.
The combination of a blue sky-like colour
temperature of 12,000 Kelvin and 650 lux
illuminance did the job here. Lighting programme 2 combined around 1,000 lux with
6,000 Kelvin to support “concentrated
work” such as major mathematical and
writing assignments or during tests. The
purpose of the third lighting programme –
which delivered 300 lux at 2,700 Kelvin –
was to “calm” students during group discussions, in activity sessions or after tests.
The measurement results were supplemented by interviews, in which students
and teachers stated how satisfied they
were. In addition, a record of pro-social and
41
aggressive behaviour was developed and
analysed by psychological evaluators.
Calmer and more focused
Under the influence of concentration-promoting light (lighting programme 2), students in the intervention group proved significantly better performers than those in
the control group. Between a first and second test, they reduced the number of mistakes made by 45 percent. The control
group, which took the two tests under ordinary lighting, improved its performance by
only 17 percent. Reading comprehension
and reading speed were also as much as
30 percent better.
The “calming” lighting situation also proved
fit for purpose. To measure agitation, the
researchers developed and applied a videobased method of optical analysis. Within
around eight minutes, the restlessness
of the intervention group was reduced by
75 percent. Over the same length of time in
42
the control group, efforts to quieten the students met with only around 10 percent success. The performance test results were
comparable, however: despite the calming
effect of the light, there was no evidence of
under-performance.
Evaluators also noted that students in the
intervention group were more placid and
sociable. The students themselves confirmed this impression. In the questionnaires, they rated themselves as less aggressive.
More research will certainly need to be conducted to underpin the present findings.
However, the students that took part in this
study gave the lighting programmes installed at their school a “good” to “very
good” rating. 70 percent would recommend
a dynamic lighting concept to teachers,
parents and students elsewhere.
Dynamic lighting enhances performance
The Hamburg study shows that biologically
effective light impacts positively on student
learning. Teachers can adjust the lighting
to the learning situation and thus stimulate
their students or keep them focused. But
light can also calm students down. Dynamic lighting eases stressful situations for
teachers and students alike – enabling both
to perform better.
[40] Daylight assists learning. Where it
needs to be temporarily excluded, biologically effective lighting ensures that students
remain alert and attentive.
[41+42] Before the first lesson, after sport
or during tests, an appropriate tailored
lighting atmosphere can invigorate students,
calm them down or help focus their minds.
33
Practical example:
Dynamic retirement home lighting
For some it is a workplace, for others a home. Retirement home lighting has to meet a whole host of different
requirements. It needs to create a homely atmosphere, support the circadian rhythms of residents and facilitate
visual tasks for the nursing staff.
Retirement home lighting needs to meet
high requirements to cater for ailments that
come with old age. Many residents’ eyesight has deteriorated. But quality of life depends crucially on how well a person can
see. Clouding of the lens alone, for example, means that older people may require
illuminances up to 1,500 lux for reading and
craft activities. By comparison, the illuminance needed for standard compliance in
an office is 500 lux.
What is more, 60 to 80 percent of retirement home residents suffer from some form
of dementia. Those affected are often restless, found constantly wandering up and
down corridors. Their movements become
progressively more unsteady and the risk of
a fall increases. People with dementia also
suffer from delusions, so they misinterpret
situations. They can easily mistake shadows on the floor for obstacles, which they
find disquieting. They also often become
disoriented or experience irregular sleepwake patterns.
Lack of occupation during the day
One frequent cause of problems for the elderly is lack of occupation. Combined with
inadequate lighting, it leads to afternoon
naps and clouding of consciousness. This
is why many retirement home residents
have difficulty waking up in the morning and
cannot settle in the evening and at night.
The situation also puts a strain on nursing
staff and calls for increased staffing levels.
As well as sufficiently bright light, biologically effective light can impact positively on
the wellbeing and activity levels of retirement home residents. In a project in Austria, manufacturers and researchers spent
15 months studying the effects of different
lighting scenarios. For the purposes of the
34
experiment, lighting at St. Cathrine’s Home
for Dementia Sufferers in Vienna was upgraded to feature three different lighting
scenes.
> Lighting situation 1 increases the illuminance from 300 Lux (standard situation)
to 2,000 lux.
> Lighting situation 2 raises the colour
temperature from 3,000 Kelvin (standard
situation) to 6,500 Kelvin in corridors and
to 8,000 Kelvin in living/dining areas.
> Lighting situation 3 dynamically modifies
illuminance and light colour according to
the time of day.
Ten luminous ceiling modules were installed, each with 12 lamps. Because conventional light sources are biologically
effective only if illuminance is dramatically
increased, the lighting designers used
special fluorescent lamps of different colour
temperatures: four of 3,000 Kelvin, four of
6,500 Kelvin and four of 8,000 Kelvin. The
lamps with the highest colour temperature
consume the same amount of energy as
conventional fluorescent lamps but are
two-and-a-half times more biologically
effective.
More active and communicative
The researchers compared the effects of
standard lighting with those of the three
new lighting situations – in each case from
the beginning to the end of the day. What
they were mostly interested in was the level
of communication among residents and
between residents and nursing staff.
The results are compelling. In all three
lighting situations, residents communicate
more intensively and participate more frequently in domestic activities. They bake
cakes and help prepare meals. Socially,
too, they have become more active. They
engage in craft activities and sing more
often – especially under high illuminance.
These changes in social behaviour alone
show that the residents’ quality of life has
improved. They also spend more time in
the brightly lit corridors, where they now
evidently feel more secure.
43
Because the residents are more active during the day, they also sleep better at night.
The biologically effective lighting supports
circadian rhythms and may reduce the
amount of sleeping pills taken. So it also
helps ease the pressure on nursing staff
and saves money that can be offset against
the increased acquisition cost of a new
lighting installation. The extra investment
needed amounts to 1.45 euros per resident
a day for a period of ten years.
The results of this project are very encouraging. More studies are now planned to
secure a more detailed understanding of
how dynamic light impacts on sleep patterns.
[43– 45] More quality of life in a retirement
home: Dynamic lighting invigorates in the
morning, creates better visual conditions during the day and helps residents relax in the
evening. It thus stabilises their circadian
rhythms and makes for a good night’s sleep.
44
45
35
46
36
Practical example:
Dynamic domestic lighting
Colours impact on the observer in various ways. Psychologically, blue has a calmative effect. However, the blue
spectrum of lamps is biologically energising. In the home, biologically effective lighting is predominantly used at
present for domestic light therapy and for gently rousing us from sleep.
No one can resist the emotional impact of
coloured light. LEDs and modern fluorescent lamp systems permit dynamic lighting
scenarios with coloured light for the home.
Different colours cast each room in the right
light, transforming it into a space that – depending on atmosphere – is the perfect
place to relax or celebrate with friends.
The spectrum determines the colour
Human beings can only see colours that
are contained in a light source’s colour
spectrum and are reflected by the object illuminated. We all know the situation: inside
the department store, it looked like the
pitch black pullover we’d been looking for;
out in the street, it was clearly dark blue.
Sunlight contains all the colours that are
visible to the human eye – but the same is
not true of all artificial light sources. Halogen lamps emit the full colour spectrum, so
they render every colour. Fluorescent
lamps, on the other hand, do not always
contain the complete spectrum.
The biological mechanisms that determine
the way coloured light impacts on human
beings have only been scientifically explained for the blue spectrum. How light
triggers emotions is still a psychological
mystery.
[46] An alarm clock that wakes you up
gently with light: 30 minutes before the
wake-up time set, it gradually gets brighter,
simulating the dawn.
Light distributed over a large area
is biologically effective
colour temperature – around 6,500 Kelvin –
is in the region of daylight.
Some scientists believe that the recently
discovered third receptor may be partly responsible for our emotional response to
colour. However, an interesting phenomenon suggests otherwise: psychologists
class blue as a calming colour but the biological effect of blue light is to stimulate.
However, lighting designers can actually resolve this contradiction. Researchers
reckon that psychological impacts are due
to individual objects and thus accent lighting, whereas biological effects are achieved
with large area general lighting. No other
kind of light reaches large areas of the
retina and thus the third receptor in the eye
of the observer.
Light alarm clock for a natural wake-up
General lighting is primarily designed to
facilitate vision while coloured light is used
only to accentuate specific details. Complete solutions for biologically effective
domestic lighting are currently not yet
available. Nevertheless, no one needs to
forgo this light. Portable light therapy
devices have been around for a long time.
The light alarm clock is a more recent
invention.
Light therapy
Many people suffer from light deficiency
symptoms during the darker months of the
year. They feel tired and listless and experience mood swings that can develop into
seasonal affective disorder (SAD). SAD can
be effectively treated at home using small
light therapy devices. Featuring a spectrum
tuned to the sensitivity of the third photoreceptor in the human eye, they produce a
biological effect by delivering particularly
intensive light in the blue region. Their
The light alarm clock is another invention
bringing biologically effective lighting into
the home. 30 minutes before the wake-up
time set, it raises the illuminance in the
room, simulating the sun’s strengthening
rays at dawn. The sleeper is woken naturally and feels rested and refreshed.
Light alarm clocks produce dimmable light
up to 300 lux. Clinical studies show that
this is the illuminance required to achieve a
measurable improvement in the way we are
aroused from sleep. In the case of SAD
patients, the improvement in their morning
mood is comparable to the effect of medication. The level of cortisol is also significantly higher than when a light alarm clock
is not used. Users are more alert and start
the day full of energy. They also get up
within an average of nine minutes. Without
the light alarm, it can take them up to
25 minutes to get out of bed.
The illuminance can be set as required, so
the light alarm clock can double as a bedside light, e.g. for reading in bed. What is
more, it can be adjusted to suit personal
wake-up needs. Those who wake too early
should choose a lower illuminance, those
who generally wake up late should opt for a
brighter setting. A selectable wake-up
sound, such as birdsong, can be activated
to support the gentle wake-up process.
37
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55
Lamp spectra
Knowledge of the biological effect of light makes it increasingly important to pay attention to the spectrum of light
generated. Lighting designers use it specifically to support natural circadian rhythms. Metrics are available to
compare light sources’ circadian impact.
Light triggers different reactions in the
human body. The spectral bandwidth ascribable to a particular impact is known as
the action spectrum. In 2002, researchers
discovered a third receptor in the eye that
responds to the blue spectrum. Its maximum action spectrum is at around 460
nanometres. Since that discovery, artificial
lighting has assumed a new significance:
new lamps with specifically tuned spectra
can now influence the biological effect of
lighting without the need for high illuminance.
38
Metrics for lighting designers
Deduced from the action spectrum, the circadian response function c(␭) (see Fig. 19,
p. 19) expresses the light sensitivity of the
third receptor depending on wavelength.
Together with the v(␭) curve, which corresponds to the brightness sensitivity of the
human eye, it forms the basis of the metrics
used for the comparative evaluation of lamp
spectra in DIN V 5031-100.
The variable is known as the circadian action factor aCV and describes how much
lamp energy is provided for the visual system and how much for the biological system. Lighting designers use it to combine –
and thus manipulate – different lamp types
intelligently to produce a biologically effective lighting system geared to the effect of
natural daylight.
Fluorescent lamps with a colour temperature of 8,000 Kelvin have a higher blue content and are as biologically effective as daylight (aCV = 1). They are combined with
conventional fluorescent lamp colour temperatures of 3,000 (aCV = 0.3) and 6,500
Kelvin (aCV = 0.9) – for example in so-called
luminous ceilings. This enables the colour
temperature of the artificial lighting to be
varied from warm white through neutral
white to daylight white and for its biological
effect to be fine-tuned accordingly.
100% –
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56
Lux for lux, daylight white fluorescent lamps
are equally energy-efficient as the fluorescent lamps in ordinary use – but they are at
least twice as biologically effective. They
enhance concentration, have an energising
effect and can stabilise our internal clock. In
the evening, however, warm light colours
help us relax. They slowly prepare our body
for the night and ensure that melatonin production is not suppressed so that we can
sleep better.
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58
[47] Spectrum of a halogen lamp: continuous spectrum with high red content
(aCV = 0.38)
[54] PLACAR lamp with 2,000 Kelvin colour
temperature with minimal biological effect
(aaCV = 0.14)
[48] Light colour 825, fluorescent lamps:
similar in appearance to the warm tone of a
dimmed incandescent lamp, it also has a
very low biological effect (aCV = 0.23)
[55] PLACAR lamp with 10,000 Kelvin
colour temperature and high biological effect
(aCV = 1.09)
incandescent-like light with low biological
effect (aCV = 0.27)
[56] Light colour 965 for light therapy:
daylight white of special fluorescent lamps
with increased blue content (aCV = 0.86)
neutral white light (aCV = 0.52)
[57] Light colour 965: daylight white light
of fluorescent lamps with improved colour
rendering properties (aCV = 0.90)
[51] Light colour 965 optimised for maximum colour rendering, daylight white light of
fluorescent lamps (aCV = 0.93)
[58] Daylight: continuous spectrum with
high blue content and high biological effect
(aCV = 0.94)
daylight white with higher blue content
(aCV = 0.98)
[53] Fluorescent lamp with 17,000 Kelvin
colour temperature: higher blue content than
daylight, correspondingly high biological
effect (aCV = 1.23)
39
59
Outlook: research intensifying
Science and industry continue to investigate light’s biological importance for human beings. But they are already
consolidating basic findings, which are increasingly being incorporated into lighting concepts.
The observed effects of light on the human
body, mind and emotions are a promising
discovery. They excite doctors and psychologists, chronobiologists, sleep and
light researchers alike. Electrified by the
possibility of addressing the human organism specifically via the eye, they are setting
the course for the future: there are good
biological reasons for being selective about
future lighting for indoor space.
ters separately, seeking to establish, for
example, the ideal size for luminaires and
illuminated room surfaces. But interest is
also focused on the right mix for a desired
effect: What are the spectral requirements
for stabilising the circadian rhythms of a
shift worker? What level of illuminance is
needed, and what length of exposure?
These are possible lines of enquiry. Sights
are set on harnessing the findings swiftly
for future lighting design.
Optimising factors for specific purposes
Early successes
The most important parameters for circadian-effective lighting are now known. The
next step is to optimise them for specific
purposes, either singly or in combination.
For this, scientists are looking at parame-
40
Pilot projects in schools, factories and offices already show that the right light at the
right time can enhance concentration and
performance. Retirement homes are also
implementing biologically effective lighting
with success: age-appropriate lighting that
varies according to time of day can demonstrably stabilise the sleep/wake rhythm of
senior citizens. An early study shows that it
can significantly reduce the use of sleeping
pills and sedatives.
of a doctor, they are likely to play a growing
role in the future, especially in the prevention of SAD. Scientists are looking closely at
what ailments can be treated successfully
with light – with no drugs and no serious
side-effects.
In the near future, new findings will lead to
biologically effective lighting becoming
practically ubiquitous. Energy efficiency will
then also be redefined: it will be measured
in terms of the balance achieved between
use of resources, ergonomic lighting and
biological effect.
Still untapped potential
Modern light therapy is also a child of intensive research. In the past, successful treatment consisted of bombarding the patient
with bright white light – especially when
combating seasonal affective disorders
(SAD). Today, the devices used stimulate
the right receptors in a more targeted and
efficient manner.
Another advance is knowing the best time
for treatment. This enables circadian rhythms
and symptoms of depression to be influenced most effectively. Light in the morning,
for example, works best against SAD.
Light therapy devices are now also available
for home use. Used according to manufacturer’s instructions and with the go-ahead
But circadian-effective lighting has more
potential than that. The harder the scientific
evidence becomes, the louder will be the
call for dynamic lighting systems that combine artificial light with daylight and harness
its biological effect in all indoor space.
In future, wherever people spend a significant amount of time in an enclosed space,
they will be supported in the tasks they perform by biologically effective light. They will
be gently awoken by light in the morning
and vitalised by it on their underground
journey to work. Their day will thus get off
to an invigorating start. Even today, dynamic lighting bridges slumps in performance and permits a gentle transition to
leisure at the end of the working day.
[59] Over the rooftops of Vienna, research
shows foresight. In future, wherever people
spend time indoors, they will be supported in
the tasks they perform by light.
41
Glossary
Action spectrum – Spectral sensitivity to
an action triggered by light. The maximum
action spectrum of the third receptor (see
Third receptor) lies at around 460 nanometres, i.e. in the blue region of the spectrum
visible to the human eye.
Adrenaline – Hormone with a stimulating
effect, e.g. on heart, vascular system or
breathing. It is produced in the adrenal
gland.
Alzheimer’s disease – The most common
form of dementia. It is accompanied by
progressive diminishing brain volume.
Biological darkness – Despite standardcompliant lighting, human biological
rhythms are not sufficiently supported in
modern day-to-day life by biologically effective light. Biological darkness is the term
used to describe this state of deficiency.
Biorhythm – Non-specific term for a
natural rhythm of biological cycles in living
organisms.
Chronobiology – The field of biology
concerned with the timing of biological
processes
Circadian rhythm – A biological rhythm
occurring at intervals of around 24 hours
(from the Latin circa = approximate, dies =
day), e.g. the sleep/wake rhythm in human
beings. Light is the most important cue
(see Zeitgeber) for synchronising circadian
rhythms.
Colour rendering – This indicates how
natural colours appear under a lamp’s
light. The colour rendering index is based
on eight frequently found test colours.
Ra = 100 is the best possible rating.
Colour temperature – The colour of the
light emitted by a lamp measured in Kelvin
(K). It is defined by comparison with the
light radiated by a “black-body radiator” at
a certain temperature. The higher the
42
colour temperature, the closer the colour is
to daylight white.
Cortisol (hydrocortisone) – Hormone
with stimulating effect on various bodily
functions ("stress hormone")
Dementia – Pathological loss of cognitive
ability that mostly affects elderly people.
Depression – Pathological emotional low
that requires treatment.
Endogenous – Originating within an
organism, not caused by environmental
factors.
Internal clock – Also known as the master
clock, it synchronises the body with the
external day/night cycle. It is located in the
suprachiasmatic nucleus (SCN). Light is
thus the most important synchroniser for
the internal clock. It uses hormones and
neurotransmitters to regulate the many tiny
clocks in body cells that have no direct
contact with the environment.
Light colour – Light colour describes the
colour appearance of a lamp’s light. Light
colours are based on colour temperature
expressed in Kelvin (K). Lamps with the
same light colour can have very different
colour rendering properties because of the
spectral composition of their light.
Epiphysis – (see Pineal gland)
Ganglion cells – Nerve cells in a ganglion
(a mass of nerve cell bodies) that transmit
visual information from retina to brain via the
optic nerve. Two to three percent of ganglion cells are themselves photosensitive.
They contain the pigment melanopsin and
trigger biological responses in the body.
Hypophysis (pituitary gland) – This
regulates the hormone balance of the body
by producing hormones itself or using
neurotransmitters to prompt other organs
to do so.
Hypothalamus – Probably the most important control centre of the autonomic nervous system, the hypothalamus is located in
the diencephalon (interbrain), where it regulates circadian rhythms via the suprachiasmatic nucleus (SCN).
Illuminance – Illuminance (symbol: E, unit
of measurement: lux) defines how much
light – technically speaking, how much
luminous flux (in lumen) – falls on a given
area. Where an area of one square metre is
uniformly illuminated by one lumen of luminous flux, illuminance is one lux.
Infradian rhythm – Rhythm with a period
longer than 24 hours.
Light emitting diodes (LEDs) – Electronic
semiconductors which, when energised,
emit red, green, yellow or blue light. Furnished with an internal luminescent coating,
blue LEDs can be made to yield white
light.
Light therapy – Treating ailments by irradiating patients with biologically effective
(including ultraviolet or infrared) light. Light
therapy is mostly used for skin complaints
and forms of depression.
Luminance – Luminance (symbol: L) is
the brightness of a luminous or illuminated
surface as perceived by the human eye.
It is measured in candelas per unit area
(cd/m²).
Luminous efficacy – The quotient of a
lamp’s radiant luminous flux in lumens (lm)
and the power it consumes in watts (W),
luminous efficacy is the measure of a lamp’s
efficiency. The higher the ratio of lumens to
watts, the better the lamp transforms the
incoming energy into light.
Luminous flux – Luminous flux (symbol:
⌽, unit of measurement: lm) is the rate at
which light is emitted by a lamp. It describes the visible light radiating from a
light source in all directions.
60
Luminous intensity – Luminous intensity
(symbol: ⌱) is the amount of luminous flux
radiating in a particular direction. It is measured in candelas (cd)
Melanopsin – Photopigment responsible
for the photosensitivity of retinal ganglion
cells. Its sensitivity can be described by the
action spectrum of melatonin suppression,
which lies at a maximum of 460 nanometres, i.e. in the blue spectral region.
Melatonin – Hormone that signals “night
rest” to the human body and makes us feel
tired. Also referred to a “sleep hormone”,
it is produced from serotonin in the pineal
gland and secreted during the night. It can
be inhibited by exposure to light during the
night.
Monochromatic light– Light of a single
wavelength creating an impression of
colour in the human visual system
Optic nerve – Neural connector via which
the rod and cone cells transmit visual information from the retina to the brain.
Photopic vision – Day vision (mainly produced by cone cells in the eye), which requires an average illuminance above around
3 cd/m2 (p. 19, Fig. 19: v(␭)).
Photoreceptors – Photosensitive sensory
cells that absorb photons and forward the
information to the nervous system as electrical signals. In the retina of the human eye,
this is done by cones, rods and melanopsincontaining ganglion cells. Cones are responsible for colour vision. Rods, because they
are more light-sensitive than cones, enable
us to see in low light. Melanopsin-containing
ganglion cells are not visual cells. They transmit light information to the central nervous
system and thus control our internal clock.
Pineal gland – Hormone-producing gland
between the cerebrum and cerebellum. It
produces the “sleep hormone” melatonin,
which it secretes into the blood at night.
Retina – Layered structure of cells lining
the rear wall of the eye. It contains the
photoreceptors (cones and rods) that convert light stimuli into visual nerve impulses
These impulses are then forwarded by
ganglion cells to the brain. The melanopsincontaining ganglion cells (third receptor)
are also located in the retina. But they
do not forward their impulses as visual
information to the diencephalon (“interbrain”) via the optic nerve ; they transmit
biological signals via the retinohypothalamic tract.
Retinohypothalamic tract – Neural
connector between the retina and the
suprachiasmatic nucleus (SCN) in the
diencephalon (interbrain), via which
melanopsin-containing ganglion cells (the
third receptor) transmit light stimuli as
biological signals.
Scotopic vision – Night vision (produced by rod cells in the eye) at luminance
levels of less than 1 cd/m2, p. 19, Fig. 19:
v’(␭).
Third receptor – Melanopsin-containing
sensory cells (ganglion cells) that are
sensitive to light in the blue region of the
spectrum and transmit light information to
the SCN and the pineal gland in the central
nervous system.
Ultradian rhythms – Rhythms with a
period spanning less than 24 hours, e.g.
sleep phases.
Visual field – The part of the environment
that can be perceived by the eye and
registered on the retina without the eye
moving.
Zeitgeber – A zeitgeber (German for
synchroniser) is any external cue that influences the internal clock. The most important zeitgeber is light, which influences
the suprachiasmatic nucleus (SCN) via the
third receptor in the eye. The SCN, in turn,
acts as a master clock, synchronising the
circadian rhythms of individual cells and
coordinating their functions. There are also
social zeitgeber such as work times.
Seasonal affective disorder (SAD) –
Pathological depression which is generally
due to lack of light in the winter months
and which can be treated by light therapy.
The symptoms subside automatically in
the spring.
Serotonin – Neurotransmitter, or messenger substance, that carries signals between
nerve cells and acts as a mood elevator.
Its production is stimulated by daylight. At
night, serotonin is biochemically converted
into melatonin by the pineal gland.
Suprachiasmatic nucleus (SCN) –
Collection of thousands of nerve cells
whose rhythms are synchronised daily by
daylight. The SCN is located above (supra)
the point where the optic nerves cross
(optic chiasm) and is regarded as the control centre of the internal clock (master
clock) that coordinates the timing of biological processes in the body.
43
Standards, literature
DIN EN 12464-1 Light and lighting –
Lighting of work places, Part 1: Indoor work
places
DIN EN 12464-2 Light and lighting –
Lighting of work places, Part 2: Outdoor
work places
DIN EN 12665 Light and lighting – Basic
terms and criteria for specifying lighting
requirements
DIN EN 15193 Energy performance of
buildings – Energy requirements for lighting
DIN V 5031-100 Optical radiation physics
and illuminating engineering – Part 100:
Non-visual effects of ocular light on human
beings – Quantities, symbols and action
spectra
DIN V 18599 Energy performance of buildings – Calculation of the net, final and primary energy demand for heating, cooling,
ventilation, domestic hot water and lighting
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Leproult, R., et al., Transition from dim to
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[61] Illuminance, colour temperature and
planarity: Biologically effective lighting solutions for indoor space are geared to daylight.
Electronic control makes for dynamism.
For this reason alone, every factor should be
considered during the lighting system design
phase.
Schumann, Sabine und Vamberszky,
Klaus, Vigilanzsteigerung und Förderung
des emotionalen Wohlbefindens durch
dynamische Lichtführung im Büro, Zumtobel Lighting GmbH, Dornbirn, 2007
Staedt, J., Kann Licht die Liegedauer in
der Psychiatrie beeinflussen, in 2. DIN
Expertenforum Wirkung des Lichts auf den
Menschen, DIN, Editor. 2008, Beuth Verlag:
Berlin. p. 39-42.
Staedt, J., et al., Einfluss erhöhter Lichtintensität auf die Verweildauer von stationär behandelten depressiven Patienten.
Nervenheilkunde, 2009. 28(4): p. 223-226.
Takasu, N.N., et al., Repeated exposures
to daytime bright light increase nocturnal
melatonin rise and maintain circadian phase
in young subjects under fixed sleep schedule. Am J Physiol Regul Integr Comp Physiol, 2006. 291(6): p. R1799-807.
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[licht.wissen 03] 40 pages on
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01 Lighting with Artificial Light (2008)
02 Good Lighting for Schools and Educational
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03 Roads, Paths and Squares (2007)
04 Good Lighting for Offices and Office Buildings (2003)
05 Industry and Trade (2009)
06 Good Lighting for Sales and Presentation (2002)
* Currently out of print
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08
09*
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11
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Good Lighting for Health Care Premises (2004)
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Emergency lighting, safety lighting (2008)
Good Lighting for Hotels and Restaurants (2005)
Lighting Quality with Electronics (2003)
Outdoor workplaces (2007)
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15
16
17
18
Ideas for Good Lighting for the Home (2009)
Good Outdoor Lighting for the Home (2009)
City Marketing with Light (2010)
LED: The Light of the Future (2010)
Good Lighting for Museums, Galleries and
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19 Impact of Light on Human Beings (2010)
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Imprint
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Acknowledgements for photographs
Numbering of photos on back page:
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Fotolia.com: cover (Sebastian Kaulitzki), 8 (Jeanne
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licht.wissen
Impact of Light on
Human Beings
19
Fördergemeinschaft Gutes Licht
Lyoner Straße 9
60528 Frankfurt am Main
Germany
phone +49 (0)69 63 02-353
fax +49 (0)69 63 02-400
[email protected]
www.licht.de

licht.wissen 19 - LightingEurope

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