More and more building owners and designers are trying to adopt circadian lighting concepts for both new and retrofitted buildings. This has the potential to positively affect human behaviour, sleep and productivity.

Light – one of the most important aspects of human life and the reason for every living creature on Earth.

Ever since the invention of the incandescent light bulb in the 19th century, the lighting of building interiors has often been taken for granted as a quintessential part of our private and professional lives. But lighting today is much more than flicking a switch when you enter your office on Monday mornings.

Today scientists aim to use lighting to curb and affect the circadian rhythm – the ‘built-in clock’ that the human brain and body use to regulate biological processes and behaviour. There is clear evidence that particular lighting solutions with specifically targeted spectral properties can enhance the quality of sleep, while others can improve alertness and thereby perhaps human productivity. When exposed to a light stimulus, the human body reacts in different ways, for example by suppressing the sleep hormone melatonin. Similarly, lighting can be used to affect our feelings, our perception of our surroundings and our overall well-being.

Daylight, the light under which humanity has evolved, provides the most effective circadian lighting. Many of the electric lighting systems sold as circadian lighting today try to mimic daylight, but usually without its full variability.

That is why many new hospitals, homes for the elderly, office buildings and even schools that are currently being developed throughout Denmark try to adapt some form of circadian or biologically effective lighting.

Tuning the light to match the research

One of these is the Risskov Psychiatric Hospital, where scientists from Aarhus University and engineers from DEM-Esbensen are working with the medical staff to develop and test suitable lighting systems aimed at reducing the use of medication and physical restraints in the treatment of patients with bipolar disorders. With the upcoming move of the psychiatric unit to Skejby, the old Risskov hospital serves as a test bed to ensure that effective and appropriate lighting systems can be installed in the new hospital environment at Skejby.

“In collaboration with DEM-Esbensen and Moto Muto, we have created a lighting system that allows us to tune the spectral composition of the light in various ways, so that we can connect it with medical research on how lighting affects psychiatric patients. We have simultaneously studied the impact of lighting on other things than health,” says Professor Werner Osterhaus.

For instance, the researchers have examined how different spectral distributions in lighting affect people’s perception of space and colours in the room. Does the room feel big or small, is it comfortable to be in, or is the lighting somehow disturbing because of its spectral distribution? Can you even see things properly?

“If medical experts then find out that a specific spectrum works better than another at a specific time of day or during a particular phase in the treatment, the lighting system can be adapted to the new settings,” says Professor Osterhaus.

Still no agreed-upon definition

Research in circadian lighting is still fairly new, although vigorous research since the early 1970s has shown correlations between light exposure and human emotion and productivity. In the past 15 years, medical research has developed a basic understanding of the recently discovered non-visual photoreceptors in the human eye and their functions for human health and well-being, and an understanding of how and why we react to the different spectral components in light. But there is still a long way to go, as some research suggests conflicting theories. This is why the Aarhus University researchers use adaptive systems.

“There is currently no agreed-upon definition of a circadian lighting system. And such a definition might, in fact, change depending on the situation for which it is employed. Circadian lighting is proposed in a lot of settings and with varied approaches. So it is perhaps too early to give clear recommendations for an adoption in building codes and standards. That is something we need to look at very carefully. But this does not mean that we should avoid installing lighting systems moving in this direction,” says Professor Osterhaus.

“We just need to clearly state what is used in any given situation, so that we and others can assess the critical parameters and their likely impact and compare different systems. We also need multidisciplinary approaches for designing the right kind of research to further investigate circadian lighting and its impact,” he continues.

Great potential for human health and well-being

Despite the increasing research evidence on the impact of appropriate lighting technology on the human circadian rhythm, it also takes time to understand the consequences and change the existing paradigms. Compared with other consumer goods, buildings have a long service life, and substantial lighting system retrofits are still rare in existing buildings. And even in new building constructions, where attempts are made to adopt new lighting technology, the result is still mostly installations with fluorescent lamps to provide the required minimum lighting levels.

“Most of the lighting systems employed in buildings today are still rather static, but some kinds of flexible systems are slowly being adopted in more and more new buildings. Systems with one correlated colour temperature, but with a dimming feature responding to the available daylight and perhaps with a control system allowing for different lighting scenarios and uses in the same room, are becoming fairly common in new buildings now,” Professor Osterhaus points out.

“Well-considered lighting has a very large potential for both human health and well-being, and for reducing the environmental impact of buildings, especially when the starting point is an effective use of daylight to provide appropriate lighting levels for most of the daylight hours,” he adds.

The lighting industry likes to refer to the latest technology, especially circadian lighting, as Human Centric Lighting. “But doesn’t most lighting target humans?” asks Professor Osterhaus rhetorically.

“In general, engineers and architects are concerned with providing sheltered, comfortable and healthy environments for people. That is and always has been the premise we work with. Until we can make definite recommendations, however, we need to be careful not to install systems that are too rigid, but systems that are flexible enough to move with new research and adapt to it,” he adds.