Lighting design for office buildings has typically focused on energy efficiency and the amount of light required for work in terms of vision. Little attention has been given to understanding how light affects health in the built environment.
Biological rhythms that repeat approximately every 24 hours are called circadian rhythms. Robust daily patterns of light and dark synchronize our circadian rhythms to local time. Disruption of this 24-hour rhythm affects every one of our biological systems from DNA repair in single cells to melatonin production by the pineal gland in the brain. Circadian disruption is most commonly linked with disruption of the sleep-wake cycle—feeling sleepy during the day and experiencing sleep problems, such as insomnia at night—but may also increase the risk for diabetes, obesity, cardiovascular disease and cancer.
In general, office lighting is designed for the human visual system, not the circadian system. Unfortunately, lighting characteristics that are effective to the circadian system are different from those effective to the visual system. An ideal lighting system for dayshift workers would provide cool, high light levels during the daytime—in particular, during morning hours. Many lighting systems currently installed in office buildings provide too little circadian-effective light during the day. This can lead to delayed bedtimes, insomnia and depression.
Circadian Stimulus Study
In 2013, the Washington, D.C.-based U.S. General Services Administration awarded a contract to the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, Troy, N.Y., to study how measures of sleep and mood are linked with measures of circadian light exposure in federal buildings. Led by Dr. Mariana Figueiro, Light and Health program director at the LRC, the study is among the first to measure personal circadian light exposures in office workers and to relate those measures to sleep and mood.
The study included 109 participants from five different buildings managed by GSA: the GSA Central Office in Washington, D.C.; Edith Green-Wendell Wyatt Federal Building, Portland, Ore.; Federal Center South Building, Seattle; Wayne N. Aspinall Federal Building and U.S. Courthouse, Grand Junction, Colo.; and GSA Regional Office Building, Washington, D.C.
During the study, the LRC researchers measured circadian stimulus (CS), the calculated effectiveness of light’s impact on the circadian system. CS is a transformation of circadian light—irradiance at the cornea weighted by the spectral sensitivity of the human circadian system, as measured by nocturnal melatonin suppression—into relative units, from 0 (the threshold for circadian system activation) to 0.7 (response saturation).
Daysimeters, personal wearable technology developed by the LRC in 2004, were used to measure the study participants’ circadian light exposure and activity patterns for one full week. The LRC also collected data on the study participants’ sleep and mood.
The results of the study show that office workers receiving CS greater than 0.3 in
the morning exhibited greater circadian entrainment, were able to fall asleep more quickly at bedtime, and experienced better quality sleep than those receiving a morning CS of 0.15 or less. Participants receiving high CS during the entire workday also exhibited reduced depression and better sleep quality compared to those receiving low CS.
Although most of the GSA buildings in the study were designed to maximize daylight availability in the space, CS exposures were typically not delivered at the desired level. Furniture placement, window-shade position, deskspace location and orientation, among other factors, can affect CS levels.
PHOTOS: Lighting Research Center at Rensselaer Polytechnic Institute