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1 licht.wissen 19 Impact of Light on Human Beings Free Download at

2 licht.wissen 19 _ Impact of Light on Human Beings 01 Contents [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. 3 Editorial 5 Human evolution is shaped by light 6 Biological rhythms 11 Our internal clock 15 Biologically effective light 16 Biologically effective light indoors 20 Light therapy 24 Lighting design 26 Lighting quality and energy efficiency 29 Practical example: Dynamic office lighting 30 Practical example: Dynamic industrial workplace lighting 32 Practical example: Dynamic school lighting 34 Practical example: Dynamic retirement home lighting 37 Practical example: Dynamic domestic lighting 38 Lamp spectra 40 Outlook: Research intensifying 42 Glossary 44 Standards, literature 46 licht.de publications 47 Imprint and acknowledgments for photographs

3 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. 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. 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.. 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 3

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5 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 [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

6 licht.wissen 19 _ Impact of Light on Human Beings 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. 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. 6 [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. 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 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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8 licht.wissen 19 _ Impact of Light on Human Beings 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. 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. 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

9 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. 9

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11 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. [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. 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 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. 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 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 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. 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

12 licht.wissen 19 _ Impact of Light on Human Beings Visual (green) and biological (blue) path visual centre suprachiasmatic nucleus (SCN) pineal gland superior cervical ganglion retinohypothalamic tract spinal cord

13 [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. 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. 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. 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 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. 13

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15 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. 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 illuminance and colour temperature of daylight change dynamically from sunrise to sunset. 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

16 licht.wissen 19 _ Impact of Light on Human Beings 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. 16 [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. 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. 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. 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 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 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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18 licht.wissen 19 _ Impact of Light on Human Beings 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 biological 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

19 oped fluorescent lamps that eliminate or emphasize the circadian wavelength range and still meet all visual quality standards. Illuminance varies dynamically 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, 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. [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 nm wavelength range. [20] PLACAR fluorescent lamp with a colour temperature of 10,000 Kelvin % PLACAR research project rel. intensity 20 75% 50% 25% 0% wavelength (nm) 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. 19

20 licht.wissen 19 _ Impact of Light on Human Beings 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 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 [21] At the doctor s, in hospital or at home: light therapy is an effective and straightforward safeguard against seasonal affective pronounced sleep/wake rhythm could be might be one of them, an insufficiently disorder. another. 21

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22 licht.wissen 19 _ Impact of Light on Human Beings 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/m 2 ). 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/m 2. 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. 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 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 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-

23 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 > 2,000 > 4,000 > 6,000 > 8,000 >10,000 >12,000 >14,000 >16, % 75% rel. intensity 50% [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. 24 0% wavelength (nm) 23

24 licht.wissen 19 _ Impact of Light on Human Beings 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. 24 Quality features 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. 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. The basic requirements are set out in the standard DIN EN 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. Light colour is crucial 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. Spatial distribution of light 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.

25 [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 [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) 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- 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

26 licht.wissen 19 _ Impact of Light on Human Beings 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. 26 [35] Interiors where daylight is utilised are ideal. Intelligent management regulates artificial lighting to supplement the daylight as required. This saves energy and costs. 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. 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 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-

27 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 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

28 licht.wissen 19 _ Impact of Light on Human Beings

29 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. Different lighting atmospheres 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. 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. The key to correct lighting is in the mix 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. 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 lighting. 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. 29