Recognition that the built environment can have a profound effect on human health and well-being is reshaping the building industry. Builders, engineers, architects and designers are rethinking every aspect of a built space for how it might either positively or negatively impact occupants.

One area showing a lot of promise is the emerging field of human-centric lighting (HCL), which studies how artificial light influences health and well-being. Recent findings suggest the interactions may be more complex and more varied than previously thought.

Research into the connection between lighting and wellness grew out of the discovery of a third set of photoreceptors in the human body. Scientists found that these receptors are sensitive to certain kinds of light and, in turn, affect levels of certain hormones, such as melatonin, which regulates our biological clock (e.g. sleepiness and wakefulness).

For example, explains lighting specialist Stan Walerczyk, a member of the Human Centric Lighting Society, "Blue light content suppresses melatonin and encourages dopamine, serotonin and cortisol production, meaning greater exposure to it during the day can lead people to be more alert and productive at work, or even during night shifts. At the same time, at night, such melatonin disruption can create sleep issues."

Subsequent studies have shown these biochemical reactions can be heightened or suppressed through the use of controlled artificial lighting. Researchers have demonstrated that altering lighting conditions can improve cognitive performance and emotional state or mood. In healthcare settings, modifying lighting has resulted in faster patient recovery, less disruption during sleep, and lower levels of depression.

Programming indoor lighting to mimic changes in natural light during the day (whiter, brighter light in the morning; warmer light in the afternoon) helps to regulate circadian rhythms and has been found to enhance workers' performance in offices and students' performance in classrooms.

Some recent findings point to other benefits of specific types of artificial lighting. A study conducted by the Lighting Research Center at Rensselaer Polytechnic Institute found nurses working under red light at night (rather than blue or bright white light) did not display negative levels of melatonin, as expected, but they also performed their work faster.

This suggests red may also act as a positive stimulus without the negative side effect of bright white light, which contains a high level of blue spectrum, and could benefit other occupations that utilize night shifts.

The Academy of Sleep Medicine recently reported on an experiment in which individuals who were exposed to blue wavelength for a period of 30 minutes displayed faster reaction times to cognitive tasks. The effects lasted up to 40 minutes after exposure to blue light had ceased. The researchers conclude blue light could be a positive environmental stimulus in settings "where alertness and quick decisions are important."

In a separate study, researchers discovered blue light also appears to affect glucose levels and thus may prove to be useful in regulating hunger, eating patterns and weight gain. And a team of researchers at Harvard Medical School testing the effects of different kinds of light on migraine sufferers found green light was the least irritating because it stimulates the optical area the least.

Much is still not understood about the ways in which light interacts with the body's various systems. These findings suggest there is no simple, one-size-fits-all solution for determining proper lighting within the built environment.

As many surveys have documented, occupants' preference is for personal control. But personal control of what remains to be determined.