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licht.wissen
Impact of Light on Human Beings
19
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licht.wissen 19 Impact of Light on Human Beings 01
Editorial
Since launching its LED Lead Market Initiative at the end of 2008, Germany’s Federal
Ministry of Education and Research has put up more than €40 million for technology and
municipal pilot projects. With the public lighting competition “Kommunen in neuem Licht”
and the two sectoral projects “UNILED” and “Performance Quality Label” (PQL), it has
shown that LED technology
쐍 is usable within the existing infrastructure without major additional investment
쐍 permits energy savings between 50 and 90 percent
쐍 is felt by users and residents to bring an improvement in lighting.
In the light of these project findings, the Federal Government has driven forward the
implementation of the new lighting technology. Under the municipal directive for energy
efficiency, the Federal Environment Ministry has supported hundreds of LED projects. In a
decree issued in 2013, the Federal Ministry of Transport made LED the lighting solution
of choice for federal buildings. The federal states (Baden-Württemberg and shortly NRW)
have started to follow suit. The LED Lead Market Initiative has thus achieved its objective.
By international standards too, Germany is a lead market for LED technology – not only
in terms of international high-profile flagship projects in Freiburg, Munich, Trier and else-
where but also in terms of euros and cents for the large number of mostly small and
medium-sized enterprises.
One of the issues closely connected with LED technology is the impact of light on human
beings. Modern testing and measurement methods enable the physiological, psychologi-
cal and social effects of light to be investigated much more thoroughly than in the past.
And with the new scope for colour control and colour rendering that LED technology
offers, the findings are much easier to harness than with conventional lighting technology.
When public utility companies marketed the new municipal gaslight in the early decades
of the 20th century, brightness – measured in “candlepower” – was pretty much the only
yardstick used. As the century progressed, luminance, illuminance, contrast rendition
and glare were added as quality criteria. Today, light colour, colour temperature and the
interplay between light, illuminated surfaces and human perception are starting to play a
central role.
In 2013, the Federal Ministry of Education and Research called for “intelligent lighting”.
sending out an invitation for basic research to be conducted in these areas. The projects
selected will be launched shortly. With the new technology, research is again an impor-
tant issue for the lighting industry. I look forward to the new lighting solutions signalled by
numerous examples in this booklet.
Dr. Frank Schlie-Roosen
Head of Optical Technologies/Photonics Division
Federal Ministry of Education and Research
3
licht.wissen 19 Impact of Light on Human Beings
Better light for a
better quality of life
Page 6
Human evolution is
shaped by light
Page 8
Biological rhythms
Page 10
Our internal clock
Page 14
Melanopic
effects of light
Page 18
Biologically
effective indoor
lighting
Page 20
Lighting quality
and energy
efficiency
Page 32
Light therapy DIN SPEC 67600:
Lighting Special Page 24 Lighting design recommendations
Page 28
4
Office lighting
Page 34
Industrial lighting
Page 36
School lighting
Page 38
Hospital lighting
Page 40
Retirement home
lighting
Page 42
Domestic lighting
Page 44
Outlook
Page 48
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Page 54
The light source spectrum Glossary Standards and literature
Page 46 Page 50 Page 52
5
licht.wissen 19 Impact of Light on Human Beings
Better light for a better quality of life
Light synchronises our “internal clock”. Lighting that copies daylight has more than just a visual impact; it supports
bodily functions 24 hours a day. We feel good, we are productive and we can sleep better.
Light does us good. We are reminded of enclosed spaces under artificial lighting that
that every year in spring: when the days normally lacks the dynamism and biological
get brighter we feel more active, we are in effect of daylight. That has consequences
a better mood and we are generally more for human health and performance: during
focused than in the dark winter months. the winter months, nearly 40 percent of
Germans experience a lack of drive and
This shows that we need light for more mood swings that can develop into depres-
than just vision. Its importance is a lot sion. Lighting that delivers non-visual im-
more far-reaching than that: It synchro- pacts can nip that development in the bud.
nises our “internal clock” – a complicated
control system that coordinates all bodily Good lighting is particularly important for
functions in a 24-hour rhythm. That control older people. Their numbers will continue to
system needs to be recalibrated daily by grow in the course of demographic change
daylight. Without light as a cue, our internal and good lighting design needs to take
clock gets out of synch. This can result in account of that. As we get older, we need
lethargy and tiredness, mood swings or more light to perform visual tasks, e.g.
even a weakened immune system. at work. But that is not all. Quality of sleep
also steadily deteriorates. Melanopic light-
Around the turn of the millennium, scien- ing and illuminance levels tailored to older
tists identified photoreceptors in the retina people’s needs have a stabilising effect
Terminology that do not facilitate vision but set our in- here – enhancing wellbeing and motivation.
ternal clock. They respond very sensitively
Chronobiology is concerned with the non-visual to light with a high blue content. The new edition of booklet 19 takes
effects of light. Many in this context speak of account of the latest research findings and
biologically effective lighting but that is not a That discovery injected a whole new presents examples of new applications.
precise descriptor because “biological” also encom- dynamism into the topic of light and health. The switch to energy-efficient LED lighting
passes visual processes. A more accurate term – Today, adaptive lighting can crucially im- and the development of intelligent lighting
one that is used in the new draft pre-standard DIN prove quality of life. Circadian lighting that control systems are not just the key to ex-
SPEC 5031-100 – is “melanopic effects of light”. brings daylight indoors and is supple- tremely energy-efficient lighting solutions.
These are the non-visual effects facilitated by special mented as required by artificial light They also open up totally new opportunities
photoreceptors containing the photosensitive 쐍 supports the human sleep/wake rhythm for supporting human functional, emotional
pigment melanopsin. 쐍 thus boosts vitality and helps us sleep and biological needs.
better
At times, the expression circadian lighting is also 쐍 promotes wellbeing and health Biologically effective lighting concepts
heard. This is a correct term where lighting is 쐍 enhances productive capacity and con- play a growing role
designed to stabilise the human day/night rhythm. centration. market study conducted by international
It should not be used for brief activating “showers management consulting firm A.T. Kearney
of light”. The right lighting helps meet for the German Electrical and Electronic
human needs Manufacturers’ Association (ZVEI) and
The term dynamic lighting is also commonly used. The advantages of dynamic lighting are LightingEurope forecasts that “human cen-
This can have an effect on circadian rhythms if shown by numerous studies worldwide and tric lighting” will command around seven
colour temperature and illuminance vary in the same a growing number of practical applications. percent of the lighting market by 2020. The
way as daylight. At the same time, however, the term Modern industrial society fosters an almost majority of applications, according to the
also describes light that changes (e.g. in colour) 24/7 lifestyle and dynamic lighting has researchers, will be in office buildings,
but has no biological impact. the ability to help us reconnect with our healthcare facilities, industry, educational
internal clock. establishments and private homes.
We no longer spend much time outdoors. Joint efforts by everyone involved are
Our lives are predominantly played out in needed to pave the way ahead. More re-
6
Model of the effects of light on human beings
search is required; so is comprehensive in-
formation about the connections between
light and health. This booklet aims to help
provide that information. Action should also
be taken by policymakers. For example,
the non-visual effects of light need to be
more fully taken into account in relevant
regulations. Designers and decision-makers
require reliable design recommendations,
such as those formulated for the first time
in the draft pre-standard DIN SPEC 67600.
Designing a biologically effective lighting in-
stallation calls for a great deal of detailed
knowledge, which needs to be reflected in
the official scale of fees for services by
architects and engineers (HOAI).
An important step has been taken. After a
ruling by Düsseldorf Higher Regional Court,
it is now possible to select and assess
not only the energy efficiency but also the
quality of a lighting installation as a criterion
for the award of public contracts. This
makes biologically effective lighting an im-
portant aspect of the quality of a building.
In future, energy performance will not be
the only rating that counts; a lighting instal- © licht.de
lation’s contribution to human wellbeing 02
will be another.
[03] Light is life: it does more than just
enable us see, it also has a direct effect on
our wellbeing and health. 03
7
licht.wissen 19 Impact of Light on Human Beings 04 8
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 200,000 years. For much of that time his sole source of light
was fire. Electric light has only been in use for around 150 years. No wonder daylight plays such a key role in
human life.
All life on Earth is spatially and temporally rhythms. The ability to do has proven a
organised. Many processes in nature are useful evolutionary skill.
rhythmic. The Earth rotates around its axis
every 24 hours and orbits the sun every Human beings have also developed a ge-
365 days. Hence the sequence of day and netically internalised awareness of the pas-
night, summer and winter. The Moon, in sage of time. At night, for example, our
turn, orbits the Earth, joining with the Sun body functions in a very different way than
to create tides and establish a monthly during the day. This was vital for survival in
rhythm. These cycles have had a major im- prehistoric times. During the day, people
pact on habitats. Many plants, for example, needed to be physically fit to go hunting
adapt their survival strategy to day and and obtain food; at night, the body needed
night. They open their flowers in response sleep and rest. Even today, our body is still
to the first sunlight, making their nectar ac- programmed to switch regularly between
cessible for insects. The insects, timing waking and sleep phases. They play a cru-
their foraging accordingly, pollinate the cial role in health and wellbeing.
plant – thus ensuring their own and the
plant’s survival.
[04– 06] Day or night, summer or winter:
light determines the rhythm of life on Earth –
including human life. In the course of The example shows that over the course of
evolution, human beings have also adapted time, organisms have repeatedly had to
and developed an internal clock. adapt their internal clock to external
05 06
9
licht.wissen 19 Impact of Light on Human Beings
07 08
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. Brightness during the day
and darkness at night provide the most important cues.
Many bodily functions are cyclical – both their individual highs and lows over the
in human beings and in other living crea- course of the day.
tures. Chronobiologists distinguish between
three major categories based on length of Shortly before we wake up, our body
cycle: temperature, blood pressure and pulse
rate rise. Around an hour later, the body
쐍 Ultradian rhythms span only a few hours. produces stimulating hormones. Doctors
Examples include times of day and know that the risk of heart attack is at its
hunger, sleep and waking phases in in- greatest between 10 a.m. and noon.
fants. But this is also the time of day when we
쐍 Circadian rhythms are geared to day and find brain teasers like Sudoku easiest and
night. They last around 24 hours (circa = when short-term memory is at its best.
approximate, dies = day). So it is a good time for an exam or job
쐍 Infradian rhythms have cycles longer than interview.
24 hours, e.g. the changing seasons.
Stomach acid production peaks between
Circadian rhythm noon and 2 p.m., facilitating digestion of a
Human beings and their bodily functions midday meal. When producing acid, the
have daily and seasonal rhythms. From stomach consumes so much energy that
individual cells to entire organs, every unit the rest of body feels fatigued.
controls its own time programme. Breath-
ing and heartbeat, waking and sleep – all But even if we skip lunch, we hit a perform-
biochemically controlled functions have ance “low” at midday. In the early after-
1009 10
noon, body and mind start to pick up more than 24 hours (see also the chart on [07 – 10] alternate but all bodily functions
again. Now, it is sensitivity to pain that page 17) For some people, the cycle is have their own rhythms – with highs and
lows at particular times of the day.
reaches its lowest level. So patients who shorter than 24 hours; for others, it is con-
are sensitive should make dental appoint- siderably longer. On the basis of these dif-
[11] Human performance curve over the
ments at around 3 p.m., not during the ferences, people are divided into what are day: body and mind are fittest around
morning. known as chronotypes. 10 a.m. and hit a low at 3 a.m.
Anyone engaging in sport between 4 and Chronotypes: “owls” and “larks”
5 p.m. gets more benefit than at any other Chronotypes are identified mainly by their
time of the day. It is the perfect time for sleeping habits. Many people are early ris-
muscle-building and fitness training. And ers – “larks” wide awake at the crack of
the glass of beer afterwards is most effi-
ciently digested between 6 and 8 p.m. This
is when liver performance peaks; alcohol
tolerance is high.
Human performance
When it gets dark, we feel tired. At 3 a.m.,
our body reaches an absolute low. Inciden-
tally, 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. Time 앶앶앸 noon 6 p.m. midnight 6 a.m.
However, the genetically programmed Based on: Schmidtke, Heinz (1993): Ergonomie, Wien © licht.de
rhythm for human beings is normally slightly 11
11licht.wissen 19 Impact of Light on Human Beings
dawn. But there are also “owls”, who need still governed by ultradian rhythms, i.e.
more time to face the new day. Their inter- phases of three or four hours’ duration.
nal clock runs significantly slower than that Children do not develop pronounced sleep
of other people. Conversely, the internal and waking phases until around the age
clock of a lark runs too fast. Its cycle may of two.
be complete within 23 hours, while that of
an owl may be as long as 26 hours. When youngsters reach their teens, their
sleep patterns change again: with the onset
Compared to the average, both groups of puberty, the internal clock ticks slower.
have a displaced sleep/wake rhythm. Larks Teenagers will go to bed later and sleep
are urged by their internal clock to get up longer in the morning, often for more than
early, owls are turned into a morning eight hours. When school starts, they are
grouch. The latter group, in particular, ex- often still not properly awake and – unlike
perience a kind of permanent “social jetlag” their teachers – in “social jetlag”. At around
if they are wrenched from sleep early in the the age of 20, sleep requirements then de-
morning, long before they have a subjective crease again to between seven and eight
sense of having slept enough. Despite hours.
external cues as work-times or daylight,
they find it difficult to adapt to the shorter From the age of 30 onwards, the quality of
rhythm of the Earth’s rotation. Each new sleep steadily declines. We sleep less
day adds to their sleep deficit, which has deeply and feel less refreshed, although we
to be made up at weekends. go to bed earlier and at more regular times.
But early risers also find their internal clock At the age of 70, these symptoms become
annoying – especially at the weekend when more acute. The older we are, the less our
they go to bed late but still wake up early in body distinguishes between day and night.
the morning as usual. Extreme chronotypes Sleep requirements remain the same but
often suffer from permanent conflict with sleep/wake rhythm gets increasingly out of
their biological clock. They are more prone synch with the external sequence of day
to illness. and night. Sleep cycles become irregular,
naps during the day a frequent occurrence.
Seasonal differences Lighting that has non-visual effects helps
Our chronobiological rhythms are also influ- stabilise the circadian rhythm, enabling
enced by summer and winter. In the dark older people to sleep better at night and be
months of the year, we tend to be less fit more active during the day.
and have difficulties concentrating. We also
eat more, so our body weight increases
and blood sugar levels rise.
The seasons also have a psychological
impact. In places with distinct seasons,
people are tenser in winter than in summer
and also generally more bad-tempered. A
daily 30-minute walk in daylight helps here.
Support is provided by circadian lighting.
However, some people do not just get
into a bit of a low mood in winter; they be-
come clinically depressed. They suffer
from SAD – seasonal affective disorder
(see also pages 24 ff).).
[12] Sleep/wake rhythms change over the
course of our life.
Rhythm and age
Young parents are often stressed and tired, [13] From birth to old age: sleep patterns
and that may well be due to the internal are shaped and synchronised by external
clock of their child. Infants and toddlers are cues known as ‘zeitgeber’.
1212
Development and synchronisation of sleep patterns
Birth
Infants and toddlers “learn” circadian
1 month rhythm from parents and environment
3 months
6 months
2 years
6 years Schooldays
10 years
14 years
Teenage years / “party time”
18 years
20 years
30 years Early start for work
40 years
50 years
60 years
Retirement: fewer psychosocial
70 years zeitgebers, lack of movement, dementia-
related weakening of circadian rhythm
80 years
noon midnight noon
Based on: Prof. Dr. Jürgen Staedt, Prof. Dr. Dieter Riemann (2007): Diagnose und Therapie von Schlafstörungen, Stuttgart © licht.de
13
13licht.wissen 19 Impact of Light on Human Beings
14
Sensitive ganglion cells
retina
Iris
blood vessels
blue-sensitive
cornea
fovea cone
rod
pupil LIGHT
red-sensitive
cone
lens green-sensitive
inner cone
membrane
melanopsin-containing receptors for
photoreceptors visual system
Photoreceptors for daytime vision are particularly concentrated Melanopsin-containing ganglion cells are distributed
in the fovea (the small depression at the centre of the retina over the entire retina; the most sensitive are in the
responsible for sharpness of vision, Ø~1.5 mm). The area contains lower and nasal areas.
around 60,000 cones but no rods.
© licht.de
15
14Our internal clock
Every human being ticks at a different rate. But we all respond to day and night. Many cells have their own
rhythm in the “concert” of the human body. However, they are 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.
Parents know the phenomenon: it is bed- Only around one to three percent of gan-
time and the children are tired but after glion cells are non-visual photoreceptors.
cleaning their teeth in the bathroom they Inside this type of cell, researchers found
are wide awake again. The cause of the a photosensitive protein known as mela-
sudden liveliness could well be the bath- nopsin, a photopigment that is also respon-
room lighting, which often has a high sible, for example, for a frog’s ability to
blue content – and a small group of light- adapt the colour of its skin to its surround-
sensitive sensory cells in the eye sending ings. Melanopsin-containing ganglion cells
clear signals to the internal clock. are distributed all over the retina but they
are particularly sensitive in the lower and
The “master clock” in our brain nasal part of it.
These so-called retinal ganglion cells are
located in the deep layers of the retina and In experiments, light-insensitive cells in
have a direct connection with the brain or, mice were transformed into light-sensitive
more specifically, with the suprachiasmatic ones after being injected with human
nucleus (SCN) of the hypothalamus melanopsin. Their response was most sen-
behind the root of the nose. The SCN is the sitive to the blue light of the visible spec-
mediator between light and the body’s trum.
response to it. It is the central control point,
the “master pacemaker” that precisely The first evidence of the new photoreceptor
synchronises the many tiny clocks in the in humans was indirect. It was found by
body. Neurotransmitters work from here, scientists irradiating test subjects for an
regulating bodily rhythms and adjusting hour and a half at night with monochro-
metabolism to the time of day. Enzymes matic light of different wavelengths and ob-
are activated or inhibited, hormones pro- serving the level of melatonin (sleep hor-
duced or prevented. mone) in their blood. A comparison of the
results obtained with different coloured light
The SCN consists of two brain nuclei the showed that blue light with a wavelength
size of a grain of rice located directly above around 480 nanometres suppresses mela-
where the two optic nerves cross. Each tonin production at night.
nucleus is comprised of thousands of nerve
cells whose rhythms are re synchronised The protein melanopsin
daily by daylight. The photosensitive ganglion cells report
light stimuli to the SCN, ensuring that mela-
The third photoreceptor tonin production slows down.
For a long time it was not clear how we
perceive these light stimuli. But in 2002 At the same time, melanopsin plays a key
scientists identified a third photoreceptor in role in the photoreceptors of the human
[14] Human beings regularly synchronise
the retina alongside the cones (for colour eye. It responds particularly sensitively to
their internal clock with the outside world. vision) and rods (for night vision) already blue light – and therefore reliably prevents
Daylight is the natural pacemaker. known. These special ganglion cells are melatonin being released during the day.
photosensitive but they are not used for
[15] In 2002, scientists discovered special vision. Their sole purpose is to register am- Light acts as a pacemaker for our
ganglion cells in the retina that do not have a
bient brightness and regulate biological internal clock
visual function. They are most sensitive in the
nasal and lower part of the retina. Rods and processes in the body in response to the So the crucial cues for regulating our inter-
cones are responsible for vision. incident light – the pupillary light reflex, for nal clock are provided by light. The signals
example, or the internal clocks. are sent through the retinohypothalamic
15licht.wissen 19 Impact of Light on Human Beings
Visual (green) and biological (blue) path
visual centre Ssuprachiasmatic
Nucleus (SCN)
pineal
gland
retino hypothalamic
tract
superior cervical
ganglion
spinal cord
© licht.de
16
Influence of daylight on the human body
3 a.m. 9 a.m.
6 a.m. noon 6 p.m. midnight 6 a.m. noon 6 p.m. midnight 6 a.m.
cortisol level melatonin level © licht.de
17
16tract, which connects the ganglion cells It also ensures that a large number of meta- we wake feeling unrested, we are tired
directly with the pineal gland (epiphysis bolic processes are wound down. Body during the day and lack energy and motiva-
cerebri), the SCN and the hypothalamus. temperature falls; the organism, as it were, tion. When the dark months of winter arrive,
The latter is probably the most important is put on the back burner. In this phase, the the process can become more acute. At
control centre of the autonomic nervous body secretes growth hormones that repair that time of year, some people develop
system. cells at night. seasonal affective disorder (SAD). Their in-
ternal clock misses its cues because the
In the evening, the pineal gland secretes Cortisol hormonal balance in the brain is upset.
melatonin, which makes us feel tired. In the Cortisol is a stress hormone, produced
morning, the level of melatonin in the blood from around 3 a.m. onwards in the adrenal Indoors, lighting with non-visual effects can
then ebbs. The first sunlight promotes this cortex. It stimulates metabolism again and support the effect of natural daylight. In a
genetically conditioned rhythm by addition- programmes the body for day-time opera- 24/7 society in particular, it plays a valuable
ally inhibiting the hormone’s production tion. The first light of the day then stimu- role in helping to stabilise human circadian
lates the third receptor in the eye and sup- rhythms.
Hormones: the internal clock’s messen- presses the production of melatonin in the
ger substances pituitary gland (hypophysis). At the same
Digestion, mood, sleep – human beings time, the pituitary gland makes sure the
are governed by complex biochemical body secretes more serotonin.
processes. Hormones regulate when food
is easily digested, when performance peaks Serotonin
and when sleep is at its deepest. Circadian Serotonin acts as a mood-elevating, moti-
rhythms are determined particularly by vating messenger. While the level of cortisol
melatonin and cortisol because they impact in the blood falls during the day in a
on the body in opposite cycles. Serotonin – counter-cycle to melatonin, serotonin helps
a natural anti-depressant – also plays a us achieve a number of performance
vital role in this biochemical process.. peaks. When daylight fades, the internal
clock switches back to night mode.
Melatonin
Melatonin makes us feel drowsy, slows If our body gets too little light during the
down bodily functions and lowers activity day, it produces only a low level of mela-
levels to facilitate a good night’s sleep. tonin. The result is that we sleep badly,
[16] Rods and cones transmit visual stimuli
Light as zeitgeber to the visual centre of the brain via the optic
nerve (green path). The ganglion cells of the
Days third photoreceptor, on the other hand, are
1 connected with the superior cervical ganglion
in the spinal cord and with the SCN by the
retinohypothalamic tract (blue path). The
with light as zeitgeber SCN uses pineal gland and hormone balance
to synchronise the body with the outside
without zeitgeber world.
10
[17] Cortisol and melatonin run opposite
to one another: Cortisol is produced in the
mornings, reaching a peak concentration
waking phase at around 9 a.m. which then steadily declines
sleeping phase during the day. Melatonin production starts
20 at night, peaking at around 3 a.m.
[18] Light synchronises our internal clock.
In the absence of the ‘prompt’ that light
provides, our body reverts to the length of
cycle determined by our genetic makeup;
30 our sleep/wake rhythm gets out of synch
with the time of day. The chart shows the
12 24 12 24 12 24 12 24 Time of day sleep and waking phases of a common
Schematic representation based on Wever, Rütger and Aschoff, Jürgen © licht.de “owl” chronotype with a genetically based
18 cycle length of 25 hours.
17licht.wissen 19 Impact of Light on Human Beings 19 20 21 22 18
Melanopic effects of light
Outdoors, at home or at work – light is essential for human life. But there is not always enough daylight available.
Melanopically effective lighting helps synchronise our bodily processes with the environment.
In a developed industrial society, people The brightness of daylight varies consider- the eye from above. Colour temperature
spend most of their time indoors with artifi- ably, depending on geographical position, also plays a crucial role: during the day, it
cial lighting, living a lifestyle that is increas- weather, season and time of day. In Central should be close to that of natural light with
ingly divorced from natural rhythms. Many Europe, most interiors could be illuminated a high blue content.
work shifts or work in windowless build- with natural light from around 8 a.m.
ings. So, like darkness at night, brightness through to 5 p.m. In the majority of cases, Another key consideration in designing
and dynamism of daylight figure less and however, the daylight admitted by windows artificial lighting for non-visual effects is the
less in the pattern of modern daily life. But does not reach deep into the room. need to deliver the right light at the right
while outdoor illuminance reaches thou- time. The greatest melanopic effect is
sands of lux even on a cloudy day, the level Lighting for non-visual effects achieved after a period of darkness, espe-
of artificial lighting provided at a workplace For technical reasons and because of the cially in the morning. Apart from supporting
is significantly lower than natural daylight. need to save energy, lighting for non-visual long-term diurnal synchronisation,
effects cannot simulate natural daylight melanopically effective light can also be
That has consequences. Too little light dur- precisely. But it can provide valuable sup- used to activate. In this case, for example,
ing the day can disrupt our internal clock or port. Studies show, for example, that illuminance and colour temperature are
cause sleep and waking phases to be less 500 to 1,500 lux illuminance can be biologi- briefly raised at mid-day or early in the
pronounced. Both have a negative effect on cally effective at a workplace. afternoon. In the evening, when activation
chronobiological rhythms and may cause is undesirable, warm light colours and
health problems. Melanopically effective lighting can either lowered illuminance prepare the body for
be additionally activated or automatically sleep.
Daylight sets the standard regulated to compensate steplessly for
Daylight defines the parameters for biologi- changes in daylight incidence. Harnessing
cally effective light: daylight enhances the quality of light,
makes for a greater sense of wellbeing and
쐍 illuminance optimises energy input.
쐍 planarity
쐍 direction of light, For light to reach the particularly sensitive
쐍 colour temperature photoreceptors in the lower and nasal part
쐍 dynamism of light over the day and the of the retina, it needs – like daylight – to
seasons. come from a planar light source and enter
[19] Light energises and influences our
Circadian lighting mood.
MAX [20 – 22] Like daylight, melanopically effec-
tive lighting changes over the course of the
day: from invigorating cool white light colours
and high illuminance levels in the morning,
the light undergoes a dynamic transformation
that ends in warm light colours and lower
brightness levels for the evening.
MIN [23] Daylight-like lighting with non-visual
effect is advisable only during the day (blue
6 a.m. noon 6 p.m. midnight 6 a.m.
curve). At night, in the evening and in the
쐍쐍쐍 daylight-like lighting with high biological effect early morning hours, light with only little bio-
쐍쐍쐍 light with low melanopic effect logical effect is correct. This avoids any dis-
쐍쐍쐍 melatonin hormone level ruption of biological processes in the body
© licht.de such as the rise in melatonin level (orange) in
23 the evening.
19licht.wissen 19 Impact of Light on Human Beings
Biologically effective light indoors
Melanopically effective lighting simulates the changes in natural daylight. Modern light sources ensure the required
spectrum, luminaires the right distribution of light and an intelligent control system makes the lighting dynamic.
Biologically effective artificial lighting should eye from above and from the front as if
be geared to the circadian rhythms of the emanating from a large dome. To be bio-
user. It needs to support the biological logically effective, artificial lighting needs
processes that define active and rest to direct light in the same way.
phases. Applications harnessing non visual
effects of light use changes in illuminance Studies have shown that the receptor can
and light colour to recreate the dynamism reach a state of saturation. So to achieve
of daylight indoors and are increasingly su- a circadian effect, it is not enough to use a
perseding static lighting solutions. punctual light source delivering high blue
content light. As many receptors in the eye
The health advice from chronobiologists is as possible need to be addressed – a re-
that everyone should spend at least half quirement that can be met, for example,
an hour a day outdoors. And as for indoor by appropriately dimensioned large-area
lighting, the message is: the more daylight luminaires.
can be harnessed the better. The ideal
setup is where windows, skylights and day- The effect is intensified where room sur-
light systems are used to maximise the faces – such as the ceiling and the upper
natural daylight harnessed indoors. Com- part of a wall – are used as large secondary
bined with melanopically effective artificial reflectors. Luminaires that radiate both di-
lighting, this significantly enhances quality rect and indirect light are suitable here.
of life and wellbeing: during the day, we Wall and ceiling washers that provide only
are more productive and focused, at night indirect lighting are also an option.
we can sleep better and recharge our
batteries. The right light at the right time
Lighting for non-visual effects can influence
Activating: bright light with a high blue biological processes in two ways. The first
content (lighting concept A) conveys a sense of
In terms of biological impact, daylight-like day/night rhythm even where daylight is in-
light with a high blue content is far more sufficient: illuminance and the blue content
effective than a warmer, more reddish light. of the light are steadily raised through up to
The light with the greatest non-visual effect mid-day and then gradually lowered again
has a wavelength of around 480 nanome- through to evening.
tres. In combination with high illuminance,
this cool blue daylight white has an invigo-
[25] Large-area luminaires direct light to the rating effect and helps us concentrate
eye in a biologically effective manner. The ac- better: it stimulates the receptors in the eye
tivating effect is enhanced if ceilings and and thus also the control centre of our
upper walls are bright and reflective. brain.
[26] Action spectrum of melatonin suppres-
sion [smel()] compared to the brightness sen-
The distribution and spectral sensitivity of Lighting concept A:
sitivity of the eye during the day [v()]: the the third type of receptor in the retina Diurnal synchronisation
most biologically effective light has a wave- show how perfectly the eye has adapted to
length around 480 nm. natural conditions. The most sensitive
melanopsin-containing ganglion cells are
[27] The ganglion cells of the third photore-
located in the rear and lower part of the eye
ceptor are most sensitive in the nasal and 6 a.m. noon 6 p.m.
lower area of the retina. This is due to the (see fig. 15 on page 14 and fig. 27 on page
쐍쐍쐍 illuminance
eye adapting to natural lighting conditions, 21). They are thus optimally positioned to
쐍쐍쐍 colour temperature © licht.de
because daylight enters the eye from above. receive light from the sky, which enters the 24
2025
Spectral response functions Addressing photoreceptors
light has no effect
100 light has little
effect
왎 melanopic
80 왎 visual
light has
good effect
Response in percent
60
40 smel() v()
20
0
400 450 500 550 600 650 700
photoreceptors in the retina, light undesirable
Wavelength in nanometres (nm) sensitive to light with high blue because of risk of
content glare
© licht.de © licht.de
26 27
21licht.wissen 19 Impact of Light on Human Beings
The second variant (lighting concept B) recommended in combination with low
can take the form of “light showers”. which illuminance. Evening light should also be
have an energising effect and promote con- directional to minimise stimulation of the
centration. Studies have shown that this melanopsin-containing photoreceptors in
activating light delivers positive results in the eye. With the right choice of luminaires
schools. Because the high illuminance is and light sources, lighting can be regulated
produced by only short bursts of power, to suit the time of day.
this is a very energy-efficient solution (see
also page 32f.). Suitable luminaires and light sources
The lighting industry today markets
Lighting concept B: numerous luminaires designed to offer a
Activation combination of different light colours and
deliver both direct and indirect light. Colour
temperature and light incidence can thus
be varied over the course of the day. The
use of different luminaires is a good alter-
native, e.g. a combination of luminous
쐍쐍쐍 illuminance
쐍쐍쐍 colour temperature ceiling elements that cast cool white light
© licht.de
28 into the room over a large area and direc-
tional spots or task luminaires that provide
With both concepts, the following should non-activating lighting in the evening.
be noted: activating light is advisable only
during the day; it should not interfere with Initially, the only light sources where it was
valuable night-time rest. In the evening, technically possible to add the increased
warm light colours (up to 3,300 kelvin) are blue content needed to address the third
29 30
22photoreceptor were fluorescent lamps. In white; it also adapts its 500 –1,500 lux illu-
the meantime, other light sources have also minance to the human circadian rhythm
been optimised for biological effect. and produces the right stimuli for the time
of day.
Light emitting diodes (LEDs) are a particu-
larly flexible option. A single LED luminaire – The required dynamic lighting control is
fitted with an appropriate module – can provided by lighting management systems.
provide a range of different white tones. Regulation of the individual luminaires is
LED lighting with dynamic colour control balanced and stepless, so change is not
thus permits a simple and efficient switch immediately perceived but has a sustained
from light that promotes concentration and biological effect. An ideal set-up also al-
light that soothes and relaxes. In this way, lows pre-programmed lighting scenes to [29 + 30] Dynamic lighting for more motiva-
biological and visual effect can be balanced be activated as required from a clearly tion: in the morning, high illuminance and
and varied as required. designed control panel or remote control cool colour temperatures tuned to incident
device. daylight stimulate our internal clock; towards
evening, dimmed, directional light prepares
Different light sources are also frequently
us for sleep.
combined. In this case, dynamic lighting is Lighting management systems can be
produced by a combination of e.g. warm easily integrated into higher-level building [31] Older people need more light than
white fluorescent lamps and daylight white systems. Fitted with daylight and presence their younger colleagues. Supplementary
LEDs. control systems, they save a great deal of light is provided by well-shielded desk lumi-
energy in combination with modern lumi- naires.
Dynamic lighting control naires and efficient light sources – and they
[32] Particularly important during the dark
During the course of a day, biologically ef- deliver the visual, emotional and non-visual months of the year: circadian-effective light
fective lighting not only varies its colour effects needed for an optimal quality of helps compensate for the weaker daylight
temperature from warm white to daylight light. stimulus.
31 32
23licht.wissen 19 Impact of Light on Human Beings
Light therapy
Biologically effective light is also used in medicine. Seasonal affective disor-
der (SAD), a mood disorder that occurs in the darker months of the year, is
already being successfully treated with light. Studies show 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 our industrialised world. No employer
would accept employees working to a
schedule determined by biorhythms. As a
result, many people struggle through au-
tumn 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 symp-
toms subside as the days grow longer in
spring but then return again in autumn.
Ravenous appetite from lack of light
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, espe-
cially for carbohydrates such as chocolate,
potato products or bread.
So scientists believe there may be several
causes for SAD: malfunctioning photore-
ceptors on the retina might be one of them,
an insufficiently pronounced sleep/wake
rhythm could be another.
[33] At the doctor’s, in hospital or at home:
light therapy is an effective and straightfor- One probable factor is that SAD patients
ward safeguard against seasonal affective are less able to adapt to the shorter days
disorder. of winter. This throws their internal clock 33
2425
licht.wissen 19 Impact of Light on Human Beings
out of kilter. Lack of available light in ab- home, however, are designed for only one illuminated surface as perceived by the
solute terms is also discussed as a con- person. human eye. Research has shown that it
tributory factor. Supporters of this theory should not exceed 10,000 cd/m2.
point to the fact that SAD affects one in The lamps are monitored by an operating
three adults in Alaska but only one in 25 hours counter. After 8,000 operating hours, The luminous face of a therapy device
in Florida. their luminous flux is around 20 percent should be as large as possible. The bright-
reduced and they should be replaced. The ness needs to be spread as evenly as pos-
However, a comparative representative beam angle of a light therapy device is sible over the luminous surface.
survey by leading chronobiologists in the specially designed to take account of the
US and Switzerland leads to a different geometry of the eye. Melanopsin-contain- Therapy devices radiate light in a wide
conclusion. The researchers found that in ing ganglion cells (see illustrations on beam so that the patient can move around
1999 a significantly larger percentage of pages 14 and 21) are widely distributed in front of the luminaire within a relatively
Americans suffered from a milder form of over the retina and most sensitive in the large area. Depending on distance from the
SAD than Swiss – despite comparable lower nasal part of it. The more receptors device, illuminance can be as much as
weather. So the study shows that SAD is are addressed, the more successful the 10,000 lux. Light is considered therapeuti-
not dependent on hours of sunshine but on treatment. cally effective from 2,000 lux upwards.
personal exposure to light. To keep our in- The colour temperature – around 6,500
ternal flywheel turning, it is advisable to Another factor to consider is that human kelvin – corresponds to that of daylight at
spend a sufficient amount of time outdoors pupils open to different degrees. So the noon.
even in winter. same luminance does not necessarily result
in the same irradiation of the retina. Finally, The rays are particularly intensive in the
Daylight spectrum therapy devices the lens of the human eye becomes more short-wave blue region of the visible spec-
For people who do not get enough daylight and more opaque with age, letting less light trum. Special glass filters cut out all harmful
during the day, light therapy devices are a through. Therapy devices thus need to be ultraviolet light. Light therapy devices can-
genuine alternative. Smaller devices are sufficiently bright. not and should not tan the skin.
also available for home or office use. What
distinguishes them from the professional Technical requirements for Light therapy suppresses
equipment used in hospitals or doctors’ light therapy devices sleep hormone
surgeries is mainly the size of the luminous Therapeutic light sources should have a So far, medical research shows that light
surface. Hospital devices are the largest. luminance of around 8,000 candela per therapy works exclusively via the eye. When
They can be used to treat three to four pa- square metre (cd/m2). Luminance is the daylight falls on the retina, the pituitary
tients simultaneously. Devices for the measure of brightness of a luminous or gland in the brain produces hormones and
[34 + 37] Light therapy devices are also
easy to use at office or factory workplaces.
[35] Luminance distribution of a light ther-
apy device with 26 mm diameter fluorescent
lamps
[36] Spectrum of a light therapy device: the
light colour resembles daylight. 34
26neurotransmitters such as serotonin. Too evening because it will cause melatonin treat premenstrual complaints, for exam-
little serotonin is a frequent cause of de- production to be suppressed and make it ple, especially the attendant emotional
pression because it works as a messenger harder to fall asleep. symptoms. There are also indications that
substance transmitting information between light therapy can help those with bulimic
brain cells. Vital functions and thought The frequency and length of therapy ses- eating disorders, especially seasonal bu-
processes work only when sufficient sero- sions required vary. The regime is pre- limia.
tonin is present. And whether they work or scribed by the doctor in consultation with
not impacts on our mental state. the patient and depends on the severity of Light looks like a promising therapeutic
the symptoms. In most cases, a beneficial tool. But one thing is certain already: light
Serotonin brightens our mood, increases effect is noted within one to two weeks. therapy is a natural anti-depressant against
our sense of wellbeing and boosts our mo- the “winter blues”, as the milder form of
tivation. To enable the body to step up the Light therapy is also an effective preventive SAD is also known.
secretion of serotonin, light therapy lamps measure for patients who suffer regularly
simulate the intensity and colour tempera- from SAD. There are no known serious
ture of daylight. What is more, they produce side-effects. Occasional complaints such
short-wave light in the blue region of the as eye irritations, headaches and dry skin
visible spectrum, which stimulates the gan- clear up after a few hours. As a general
glion cells of the third photoreceptor in the rule, however, anyone considering light
retina. These then inhibit the production of therapy should first have a word with an
the hormone melatonin. As a result, we are ophthalmologist because caution is advised
alert and productive during the day and in the case of certain eye disorders.
sleep better at night. Melatonin thus sta-
bilises our circadian rhythm. The artificial Great potential of light therapy
lighting normally found at a workplace is Light therapy has recently been used to
not usually enough to achieve this effect. cure a variety of ills. There are even reports
of Parkinson’s and Alzheimer’s patients
Light in the morning is the most effective being irradiated with biologically effective
Light therapy is best administered in the light, although there is currently no clear
morning. It tells our biological clock that the scientific evidence of therapeutic efficacy.
day has begun and that bodily functions
need to be activated. Conversely, it is not What studies do show, however, is that
a good idea to apply light therapy in the light therapy can be successfully used to
35 > 2,000 > 4,000 > 6,000 > 8,000 > 10,000 > 12,000 > 14,000 > 16,000
rel. intensity
wavelength (nm)
36 37
27licht.wissen 19 Impact of Light on Human Beings
38
DIN SPEC 67600:
Lighting design recommendations
Professional lighting concepts today have the ability to create biologically effective lighting indoors. To ensure that
the light really does have a melanopic effect and at the same time provides comfortable visual conditions,
lighting designers need to pay attention to a number of factors. Design recommendations are provided in the draft
pre-standard DIN SPEC 67600.
Good light helps us perform our daily “Beleuchtung” also need to be taken into
tasks. At a desk, at a machine or in an account. The ASR concretises the health
operating theatre, light needs to provide and safety requirements that need to be
optimal task area illumination and permit met for employees at work.
fatigue-free work. Biologically effective
lighting also needs to meet all visual quality DIN SPEC 67600 facilitates planning
requirements. If lighting is to be melanopically effective,
light colour, illuminance and direction of
General quality features light also need to be adjustable. Preliminary
A good lighting installation tailors illumi- design recommendations are provided by
nance to the visual tasks that need to be the draft pre-standard DIN SPEC 67600
performed and distributes luminance published in April 2013, which takes ac-
evenly in the room. It limits direct and count of current research findings and suc-
reflected glare and delivers light with good cessfully trialled applications.
colour rendering properties. That light does
not flicker and takes account of incident In conformity with DIN EN 12464-1, DIN
daylight. SPEC 67600 looks at the use of biologically
effective lighting for different interiors,
The basic requirements that lighting needs task areas or activity zones and makes rec-
to meet are set out both in the DIN 5035 ommendations for “living spaces”. which
standards series and in the standard DIN may be work premises or non-work prem-
EN 12464-1 “Light and lighting – Lighting ises. The pre-standard refers exclusively to
of indoor work places”. These standards non-visual effects mediated by the eye –
stipulate maintained values for the relevant as a result of exposure to daylight, artificial
lighting variables and define minimum re- lighting or a mixture of the two. Information
quirements for good lighting quality. For about the melanopic action factor of
work premise in Germany, the requirements modern light sources is provided in DIN
of workplace regulation ASR A3.4 SPEC 5031-100 published in 2014.
2839
Lighting quality features according to DIN EN 12464-1
Holistic lighting design
Designing a biologically effective lighting Classical quality features
installation is a challenging task. For this
reason, DIN SPEC 67600 recommends
integrated, holistic lighting and spatial plan-
ning. This ensures that room use and the
effects of light are considered in the design
process from the outset and that all sys-
tio -
bu right
tems and materials are suitably coordinated.
n
Lig
Vi s
dis s b
hti
Holistic design also helps ensure – e.g. by
t
ss iou
ng
ua
for
tri
appropriately harnessing daylight – that a
ne mon
lev
lp
om
lighting installation that has circadian effects
el
er
r
Ha
lc
is energy-efficient (see also page 32f.).
for
ua
ma
Vi s
The design recommendations in DIN SPEC Good
g
nc
Gl
rin
67600 mainly relate to places where people
a re
lighting
e
de
en
spend a good length of time, e.g. indoor
lim
rr
ita
workplaces and communication zones or
lou
tio
high-footfall areas in care facilities. Design
Co
n
needs to take account of daily and monthly
Light Direction
rhythms as well as the seasons and the Modelling
colour of light
orientation of buildings.
Visual ambience
Melanopic effects are achieved by
쐽 higher illuminance
쐽 a higher blue content
More lighting design criteria
쐽 planar light sources
쐽 time-variable dynamic light and
Daylight integration Energy efficiency
쐽 correct timing: biologically effective light
is most effect in the morning, after hours
Change of lighting situation Scope for personalised settings
of darkness.
© licht.de
Light colour is crucial 40
Light colour is expressed as a colour
temperature in kelvin (K). It indicates the [38 + 39] Biologically effective lighting [40] DIN standards and workplace regula-
makes for a greater sense of wellbeing, pro- tions (ASRs) identify features that in toto
intrinsic colour of the light emitted by a
motes health and boosts performance. Bio- define the quality of a lighting installation.
light source. For comparison: the colour logically activating and relaxing light alternate They also need to be taken into account in
temperature of the sky generally varies over the course of the day, simulating the the design of melanopically effective lighting.
between 6,000 and 10,000 kelvin. changes in natural daylight.
29licht.wissen 19 Impact of Light on Human Beings
The light sources used for biologically effec- Because melanopsin-containing ganglion
tive lighting need to have similar colour cells are particularly sensitive in the lower
temperatures so that, like daylight, they can and nasal part of the eye, bright planar
optimally address the relevant photorecep- lighting in the upper part of the visual field
tors in the human eye. This is achieved by is recommended.
daylight white light sources with a colour
temperature above 5,300 kelvin. They have This is achieved with
a higher blue content and are much more 쐽 glarge windows, skylights and daylight
circadian-effective than warm white light. control systems for brightening the ceil-
For activating light, fluorescent lamps and ing;
LEDs are an appropriate choice. 쐽 large-area luminaires or luminous ceilings;
쐽 luminaires casting indirect light over large
Illuminance areas, so that the ceiling and the upper
Although blue spectral content is crucial for third of the walls are illuminated;
achieving a biological effect with artificial 쐽 back-lit transparent materials such as lu-
lighting, light colour is not the only factor minous ceilings, skylights with artificial
that needs to be considered: another key light, light boxes or net curtains;
variable is illuminance (measured in lux (lx)). 쐽 lighting with indirect light components on
What counts is the vertical illuminance at room elements and furnishings.
the observer’s eye, which is largely defined
by the perceived luminance of the surfaces The right light for the time of day
observed: for compliance with DIN SPEC Every human being has his or her own indi-
67600, it needs to reach at least 250 lux at vidual day/night rhythm, which is regularly
8,000 kelvin because anything less has no synchronised by daylight. For most people,
significant demonstrable biological effect. light with a stimulating biological effect is
At other colour temperatures, illuminance useful mainly in the morning. Dynamic light-
needs to be adjusted according to the new ing can either simulate the changes in
DIN SPEC 5031-100. daylight and steadily raise illuminance and
the blue content of the light through to
Spatial distribution of light mid-day or it can support activities during
For light to have a biological effect, our the day by varying illuminance and light
eyes need to be able to perceive bright colour at particular times. Periodic changes
areas in the room as effectively as possible. in lighting must always be designed with
41 42
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