As diurnal animals, humans have an evident need of light to be able to function in their environment. What is less obvious is that light also has a role in regulating wakefulness and sleep, referred to as the non-visual effects of light. This field of research has been initiated, among others, by my colleague Professor Rikard Küller who died last year. As early as the end of the seventies, he was studying how we are affected by spending time in windowless premises under different lighting conditions.
Today we know that light has an important role in regulating our wakefulness, and the obvious question is what type of light and how much. This question has also become highly topical just now since tremendous technological development is taking place in the field of light sources. We are phasing out incandescent light bulbs in favour of more efficient light sources. Through the EUP Directive, the EU is today specifying minimum requirements for the efficiency (lumen/W) of light sources. This means that the normal incandescent bulb will be gradually phased out and replaced by halogen lamps, compact fluorescent lamps and, not least, by light sources based on LED (light emitting diode) technology. An LED gives much more light per installed load.
The Swedish Energy Authority and others are at present investing in a programme called Energy Efficient Lighting. The vision of the programme is that research must be instrumental in creating a lighting environment that is not only energy efficient but also promotes human health. Within the framework of this programme, a centre for energy efficient lighting – Ceebel – has been formed with the aim to gather together researchers from different disciplines such as engineering, medicine, social sciences and the humanities and to disseminate the research results to different users. As indicated, this lighting research is interdisciplinary in character, and development over the past ten year period has been rapid.
Light regulates wakefulness and sleep
A breakthrough in the knowledge of the non-visual effects of light occurred in 2002 when David Berson of Brown University could demonstrate that, apart from rods and cones, there is a third type of receptor in the retina which probably acts as receptor for the regulation of wakefulness and sleep. Other researchers, among others George Bainard, Jefferson University, have shown that, for the regulation of wakefulness and sleep, the eye is most sensitive to light within the wavelength region 460-480 nanometres (nm), i.e. within the blue region.
Daylighting is utilised. In modern buildings better use is made of daylight than in older buildings. Photographer: Pia Laike
Daylighting is important
As early as 1992, Rikard Küller showed in a comparative study financed by the then Council for Building Research that schoolchildren in windowless classrooms exhibited a chronobiological pattern over the year which was different from that in children in classrooms with windows. The behaviour of children was also affected indirectly. When cortisol levels were higher, children worked better in groups and helped each other more than when the levels were lower.
More helpful in daylight. As early as 1992, Rikard Küller showed in a comparative study that schoolchildren in windowless classrooms exhibited a chronobiological pattern over the year which was different from that in children in classrooms with windows. Cortisol levels were higher in classrooms with windows. In these, children worked better in groups and helped each other more than in the windowless rooms. Photographer: Richard Külle
Other studies have confirmed the significance of daylight. We know today that with a sufficient amount of daylight our biological clock works faultlessly. Our research team, together with researchers from University College London and Fagerhult AB, carried out a study in the UK where schoolchildren aged 11-12 in four different classrooms were monitored over a whole year. The sleeping habits and degree of wakefulness of the children, their chronobiological markers (melatonin and cortisol) and their performance in reading, writing and mathematics, were investigated. Their energy use was also measured continuously. Two of the classrooms conformed to the latest research findings with a higher ambient light, while the control classrooms were only given new light fittings. The light in the experimental classrooms was also controlled.
Preliminary results from the study again show that daylight is an important factor for all variables, both biological and performance related ones. We could also show that no negative results were obtained with regard to the performance of schoolchildren when energy use was reduced. Physiological data are now being processed.
Just enough lighting is best
In a laboratory study, we investigated how different levels of ambient light affected test subjects both emotionally and physiologically. We had fixed illumination within the working area at the desk (500 lux) but a variable light on the front wall of the room: 20, 100 and 350 cd/m2 , where cd/m2 is the luminance, i.e. the quantity of reflected light from the wall. Lighting was provided by fluorescent tubes of type T5 with two different colour temperatures. The colour of light that we measure in °K is warmer (red/yellow) at lower colour temperatures and colder (more blue) at higher colour temperatures. We used 3000 °K (warm light) and 4000 °K (cold light). Half the test group received the warmer light and the other half the colder light, since we were also interested in studying the effect of different colour temperatures.
The results showed that there is a relationship between ambient light and cortisol levels after a day's exposure: The brighter the ambient light, the higher the cortisol level. Subjectively, the test subjects also experienced a higher activation level as the ambient light increased. We found, however, that when the test subjects evaluated their feelings, they mostly had negative feelings at the highest ambient light, and they felt most positive at 100 cd/m2. As regards colour temperature, we only found clear differences such as warm or cold in the perception of the colour temperature of light. On the other hand, we found no hormonal differences. If our results are compared with earlier research, we find that studies had been made where the test subjects could themselves set the level of ambient light, and the studies show that most people choose a level between 80 and 100 cd/m2. With regard to the significance of colour temperature the results are more contradictory. At present there is no support for the view that a cold fluorescent light would make us feel more awake, but further research is needed in this respect. In this context it is important to have knowledge of the spectrum of the individual light source.
LED outdoors
Research today often concerns the new light source LED. Research is now in progress regarding both its non-visual and visual effects. LED are often seen as an alternative to outdoor lighting, and my colleague Maria Johansson has just started a study in which the situation before and after the change to LED light sources in a housing estate are compared. The results from this and other research are continually presented at the Ceebel website: www.ceebel.se.
Higher performance when the walls and ceiling are lit. In a study in the UK where schoolchildren aged 11-12 in four different classrooms were monitored over a whole year, the sleeping habits and degree of wakefulness, as well as chrobiological markers of the children (melatonin and cortisol), were measured. Their school performance in reading, writing and mathematics was also studied. Two of the classrooms complied with the latest research findings with a higher level of ambient light, while the control classrooms were only given new light fittings. Preliminary results from the study again show that access to daylight is an important factor for all variables, both biological and performance-related ones. Photographer: Tommy Govén
Effective lighting
Apart from the effect of light on us humans, the way in which we handle and control light is also significant for how energy efficient lighting will be. In the school study described above we could show that, with effective control of light, more light need not mean a higher energy use. In a Formas project we are now working on the control of light in public environments. This work, which examines the interface between people and the control equipment, is performed by Pimkamol Maleeptiwan, postgraduate student in environmental psychology. In public environments it is important that people should easily understand how the light is regulated. Unfortunately, this is not always the case. In the course of this work we have seen that the light is on all day because nobody knows where the switch is situated. How switches and control devices should be designed are questions that will be answered in the doctoral thesis.
The significance of daylight
International research in the field of lighting has developed to a very high degree in the latest ten year period. Research results can, to a certain extent, already be used in practical work on the planning of lighting installations. At the same time, as described earlier, there is rapid technological development which means that new light sources must be tested. The significance of daylight must not be underestimated, and it is important that architects and planners have knowledge of this and make use of daylight in their designs. This will provide the conditions for both a human environment and careful use of natural resources.
Author
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Thorbjörn Laike
is Assistant Professor in environmental psychology at the Department of Architecture and Built Envirionment, Lund University. He is also deputy head of department and is chaiman of Centre for energy efficient lighting