Today, a hot topic in the lighting industry is the relationship between light and human health, which may impact lighting design choices.
Light has a number of health impacts, most notably a trigger for the body’s circadian system, which regulates sleep-wake cycles, core body temperature and the release of hormones like melatonin. Circadian disruption can produce negative effects such as poor nighttime sleep and greater risk of depression. Good circadian regulation can produce greater alertness and reduced sleepiness during the day, better sleep at night and other positive health outcomes.
According to the Lighting Research Center, four main characteristics define light’s impact on circadian health. These are intensity, spectrum, timing and duration.
- Intensity: This is the amount of light falling on the eye’s photoreceptors during the day and may be the most important entrainer. What’s of interest here is vertical not horizontal light levels. A higher light level is desirable in the morning and a lower light level in the evening.
- Spectrum: This is the wavelength of the light, typically associated with related color perception. The circadian system is most sensitive to short-wavelength (“blue”) light. Spectrum can enhance the effect of intensity.
- Timing: This is when the light is received. Light received in the morning will have a different effect on sleep time than if received in the evening.
- Duration: This is the length of exposure. The circadian system responds to the cumulative quantity of light received during the day.
A lighting design supportive of circadian health, therefore, would emphasize vertical illumination (task lighting and light reflected from vertical surfaces such as walls). The design would be capable of producing a higher intensity of light in the morning, which may be enhanced with short-wavelength light. The lighting should be controllable so as to program the timing of exposure.
However, note there is no panacea here. One size does not fit all. Additionally, nighttime light exposure is as important as daytime exposure. People should be exposed to very low light levels, which can be enhanced with higher-wavelength (“warmer”) light, starting about two hours before normal bedtime. Even then, lifestyle is the major determinant. A building lighting design that supports circadian health therefore should be seen as a measure that facilitates rather than fixes.
As a result, the ideal applications for circadian lighting are highly controlled environments occupied 24/7 on a predictable schedule, such as assisted living and nursing homes. In these applications, the lighting system can be tuned throughout the day. Schools are another interesting application, though children and their parents must be informed about good lighting practices at home.
In short, the lighting industry is capable of delivering designs that facilitate circadian health, providing an important piece to the puzzle.