By: Craig DiLouie
The biggest impact light has on human health is the circadian system, which regulates body functions based on circadian rhythms that are in turn based on the 24-hour day/night cycle. As a key example, exposure to light affects the timing of hormones like melatonin, which regulates sleep. The light enters the eye through special photoreceptors tied to the brain’s master clock. In the modern age, electric lighting plays an even more important role in circadian rhythms than daylight. The uncertainty of light exposure can disrupt these rhythms, which can lead to poor sleep and negative health effects. As a result, the lighting industry is beginning to show increasing interest in lighting design that satisfies visual needs and promotes circadian health.
When it comes to light and health, what do we know, what don’t we know, and what is actionable?
Marianna Figueiro, professor and light and health program director at the Lighting Research Center at Rensselaer Polytechnic Institute, said lighting that is well designed to support circadian health can promote not only alertness and reduction in feelings of sleepiness during the day, but also improved sleep for people with Alzheimer’s disease. She added that there are four main characteristics that affect light’s impact on circadian health: intensity, spectrum, timing, and duration.
Providing 80 to 120 horizontal footcandles is at odds with current practice and energy codes. Providing 30 to 40 vertical footcandles entails lighting vertical surfaces such as cubicle walls (daylight is ideal). Task lighting can help, as can lighting controls.
These mechanisms are becoming clear and allow lighting practitioners to design lighting systems more conducive to circadian health. However, other factors come into play, such as nighttime light exposure and lifestyle. As a result, lighting should be considered as playing a supporting role in supporting circadian health. Ideal applications in which to start include facilities occupied 24/7 on a predictable schedule, such as assisted-living facilities and potentially schools.
*For more information, visit http://www.lrc.rpi.edu/researchareas/index.asp