Circadian Light For Your Health

The use of day-lighting in buildings has focused primarily on reducing energy consumption and providing pleasant interior environments. However, light, especially daylight, may be good for one's health through impacts on the body's circadian rhythms. Given that people spend a majority of their waking hours indoors at work, daylight- if appropriately engineered and supplemented by electric light when necessary - may have unrecognized health benefits for millions of federal employees.

What are Circadian Rhythms and Circadian Light?

A person’s "body clock" is regulated by circadian rhythms, which are physiological processes that occur approximately every 24-hours. These 24-hour rhythms have also been widely observed in plants, animals, fungi, and even bacteria. An example of a circadian rhythm is a person’s wake/sleep cycle. A function of light is to entrain the body’s circadian system to the solar day so that the wake/sleep cycle is in synch with the natural light/dark cycle on Earth. Circadian stimulus is a function of the light stimulus entering the eye and the body’s biological response to that light stimulus. It takes into account the total light spectrum, time of day, and the duration of light exposure.If a person's circadian functioning is entrained, a person sleeps well at night and is alert during the day. On the contrary, a person who does not receive adequate circadian stimulus will experience poor sleep quality and will typically be sleepier during the day.

Purpose of GSA's Circadian Research

GSA's research is focused on identifying the links between the circadian stimulus people receive at work and their wake/sleep patterns, daytime alertness, and emotional functioning. GSA's overall goal is to identify specific health benefits of lighting practices that can be replicated in new and existing buildings to achieve innovative, cost effective ways to improve employee health and well-being at work.

GSA is conducting this research in two phases. The first phase consisted of taking both space and personal circadian light measurements, and the results showed that while daylight is valuable, it is an insufficient source of circadian stimulation when used alone due to numerous reasons including occupant behavior (window shade use, umbrellas), interior design, low levels of daylight penetration, and other circumstances. The second phase of the research is now exploring the added use of electric lighting solutions and other best practices that can be readily adapted to existing spaces to improve circadian functioning of all the occupants. GSA is currently conducting circadian lighting interventions at workspace occupied by the Federal Highway Administration as well as a Department of Veterans Affairs Medical Center using several different types of supplemental lighting to test whether minimum circadian stimulus levels can be achieved in windowless environments.

Buildings Studied

In the first phase, GSA conducted its research in five of its buildings in different geographical locations and in both the summer and the winter to account for seasonal variability in daylight. For more information on each of the study sites and the research findings, please visit the links below.