We need light to see things. But the light that enters our eyes also affects our well-being and health. To use light's positive health effects in buildings, the traditional criteria for lighting design must be expanded. Daylight in particular then takes on an entirely new significance. Our transition from outdoor to indoor society began only a few generations ago - and thus we have had no appreciable chance to genetically adapt to this change. Indoors, especially in the morning, important spectral components are lacking at the human eye in the intensity needed for the body to adjust its activity and performance. At night, however, humans are much more sensitive. So a stimulus that would be too low during the day impedes crucial nocturnal regeneration. The illumination levels that have been common for indoor spaces until now thus need scrutiny from a physiological point of view.
Scientific basis
As for almost all organisms, the day-night rhythm is also essential for balancing activity and regeneration in humans. Our internal clock is regulated by the suprachiasmatic nucleus, a small region of the brain directly above where the optic nerves cross. The brightness level of one's personal surroundings synchronises it with the outside world.
The light stimuli needed for this are not received by the rods and cones, which are responsible for night and colour vision, but by a third type of light receptor in the retina that was discovered in 2001. Compared to the other two types, this receptor reacts rather slowly to changes in brightness. These cells contain the light-sensitive pigment melanopsin, hence the non-visual effect of light on the eye is called the melanopic effect.
Based on current knowledge, most notably blue spectral components influence people's hormonal balance and day-night rhythm. The right light at the right time can increase well-being and concentration and reduce the frequency of errors and accidents. It also protects health in the long term, for example by improving sleep quality. Studies in MRI scanners show the activating effect is directly related to lighting and leads to increased metabolism in several brain nuclei. Conversely, the wrong light at the wrong time can significantly impair health and well-being.
The human body is a predictive system. If it can prepare its subsystems for work, sports or sleep, the same performance will cause much less stress than an unexpected transition to those same activities. Light, with its melanopic effect, plays a central role in the body's task planning.
The medium- and long-term effects of light, however, are generally not caused by a single light situation. Each place a person visits throughout the day and night contributes to the overall light exposure. Thus the melanopic effect also depends on a user's personal light history.
Quantitative evaluation of biological effects
Due to this topic's great practical significance, the International Commission on Illumination (CIE) has published initial recommendations for quantitative assessment of the melanopic effect of diverse light sources (CIE TN 003:2015). The visible radiation emitted by a light source is weighted according to its spectral composition. The unit of measurement is the melanopic weighted quantity of light per area in W/m2.
On this basis, the German Institute for Standardization (DIN) has also published initial recommendations as specifications for lighting design (DIN SPEC 5031-100:2015-08 and DIN SPEC 67600:2013-04). In Germany, the melanopic daylight equivalent illuminance (MDEI) is used in accordance with the CIE assessment method. It is typically measured vertically at, or calculated for, the eye point of a user. Put simply, an MDEI of 1 lux corresponds to 1 lux of daylight (our reference light source from a biological viewpoint) measured outdoors.
The statements about effect pertain only to the light source, however. Before daylight reaches the user's eye, for example, it usually passes through several panes of glass and is reflected by surfaces enclosing the space. In doing so, its spectral composition changes. Thus a pale yellow wall reflects a lot of light - but the melanopically relevant component might be lower than with a seemingly darker grey wall. This is likewise applicable for materials, such as when comparing wood and concrete surfaces. In addition, the melanopic effect increases when more retinal surface is illuminated. This means, for example, that expansive luminous or indirectly illuminated surfaces trigger greater stimulus than accent lighting of the same intensity.
Carpentry workshop in Landsberg am Lech
In 2014, a new production and administration building for the IWL workshops for people with disabilities went into operation in Landsberg. Construction and monitoring of the building, designed by Hermann Kaufmann Architekten, was sponsored by the German Federal Environmental Foundation (DBU). A key topic was integrating a biologically effective lighting solution and evaluating its effect on the employees.
During the planning process, it was possible to increase the amount of daylight inside by 40 %, but in some areas, that is still not enough to provide the needed non-visual stimulus of 240 lux MDEI, especially in winter. A direct-radiating, energy-efficient LED lighting component with 4,000 K colour temperature ensures horizontal illuminance of 500 lux at the work surfaces. Time-controlled indirect lighting (with 17,000 K) aimed into the sawtooth roofs is turned on between 8 and 11 a.m. This, together with the direct lighting, provides the equivalent of 240 lux of daylight at the user's eye. To minimise energy consumption, the direct and indirect components are dimmed as daylight increases. With an annual consumption of approx. 6.4 kWh/(m2a), the system also proved to be energy efficient. With a non-daylight-controlled solution commonly used in 2013, the energy demand would have been 12.5 kWh/(m2a) .
Evaluation by the Munich University of Applied Sciences showed the artificial lighting system had significant positive effects on night sleep quality and users' individually perceived well-being, which was also expressed in conversations with employees. They described the indirect light, which is evocative of light from the sky, as their feel-good light.
Study room in Munich
The Munich University of Applied Sciences turned three 75 m2 rooms on consecutive floors of a laboratory building into identical study rooms. With generously sized windows as well as ceiling-mounted panel luminaires and acoustic panels, the rooms accommodate up to 42 students.
In 2018, one of the rooms was optimised for the non-visual effect of light, with the goal of increasing students' daytime alertness and concentration and improving their night-time sleep quality. The light sources in the panel luminaires were replaced by variable-colour LEDs and supplemented by narrow-beam spotlights over the tables. A controller actuates and dims the artificial lighting components according to the time of day and the amount of daylight available. With more than 240 lux MDEI, the non-visual channel is activated even on winter mornings. In the evening, by providing 25 -100 lux MDEI at the eye with 500 lux at the work surface, the luminaires permit comfortable working and foster a healthy night's sleep. The comparison systems in the other two rooms provide a constant average of 150 lux MDEI. Despite a slightly higher installed capacity, the energy demand for artificial lighting in the room was actually reduced via more efficient lighting technology and task-oriented spot illumination.
Initial reactions are highly positive - not least because the spotlights also bring added brilliance and light quality to the room. The expected effects are currently being verified with questionnaires and test series in which students from other study rooms are included as a control group.
Refurbishment of a nursing home in Berlin
Abrupt mood changes, sleep problems, restlessness, and anxiety in the dark - all part of everyday life for people with dementia. Irrespective of any illness, elderly people's limited field of vision and progressive cataracts mean they need more light than young people. So the 2017 refurbishment of Bischof-Ketteler-Haus in Berlin introduced a dynamic artificial lighting system. The rooms were designed to be much brighter than required by standards. Ceiling-mounted panel luminaires with an indirect component illuminate the corridors with a light intensity of 500 lux. In the common areas, dynamic lighting helps stabilise the residents' day-night rhythm. The luminaires are regulated to emulate the natural course of a day. In the morning, warm light of 2700 Kelvin enables a gentle start to the day. By midday the blue component, and thus the colour temperature, rises to about 6500 Kelvin, which has an activating effect on the residents. In the evening, the system changes back to a warm colour temperature, which has a calming effect and aids in falling asleep. In the medium term, this colour temperature progression stabilises the residents' individual biorhythms, enabling them to sleep better at night and be more active during the day.
Guidance for planning
The projects presented here show that beyond the usual requirements, a high-quality solution for daylight and artificial light also requires attention to non-visual effects of light. This holistic form of planning is referred to as Integrative Lighting or Human Centric Lighting (HCL).
In point of fact, all artificial lighting systems also have a melanopic effect, but it is usually wholly unplanned. Standard-compliant lighting ordinarily achieves the required 500 lux on the horizontal work surface, but only around 100 -150 lux MDEI at the user's eye. This is usually too little in the morning but too much at night.
In order to define precise specifications for the lighting, it is necessary to clarify in advance what activities will take place in the building and at what times. Greatly simplified, the stimulus in the morning should be as high as possible for several hours (≥ 240 lux MDEI at the eye). Melanopic stimulus continues to have a positive effect even at noon and in the afternoon, albeit to a lesser extent. In the evening and at night, however, the stimulus should be minimised. These rules of thumb must, in any case, be checked and possibly adapted, depending on the specific building project. Office workers have different needs than students, people in a care facility or even shift workers.
Reliable adaptation of the MDEI requires simple but precisely adjustable time control of the artificial light. Daylight naturally offers the necessary dynamics, but targeted optimisation of facades and interiors is needed to maximise the amount of light at the user's eye. This is achieved by using glazing of high visual transmittance - within thermally sensible bounds - and with a facade geometry and interiors that favour extensive daylighting. Depending on various other factors (geographical location, position and time spent in the space), sufficient non-visual stimulus can thus be achieved for 80 % of the year.
Especially in the winter months, supplemental artificial light is essential, as we no longer adjust our daily working hours to the length of the day. More light also means higher investment costs and possibly increased energy consumption, but through good planning and by accounting for daylight in the lighting control, any additional consumption is usually moderate. In return, the added investment yields a higher-quality lighting solution that is technologically sustainable and based on the latest knowledge.
Integrative lighting involves not only selecting luminaires and components, but also defining the size and disposition of windows, the spectral quality of glazing, the positions of use zones within a space and the materials enclosing it. To optimise these parameters, partners who can quantify the impacts and interplay of designs in terms of lighting technology are needed early in the project. With an understanding of design goals and costs, the aim is then to jointly develop solutions that put good architecture in the interest of the user in the right light - at all times of the day.
