By: Craig DiLouie
New study explores the connection between light exposure and sleep, depression, and stress in office workers
A recent study by the Lighting Research Center (LRC) found that office workers who receive a strong dose of circadian-effective light in the morning experience better sleep and lower levels of depression and stress compared with those who spend their mornings in dim or low light levels.
The human circadian system generates and regulates bodily functions based on 24-hour cycles in turn signaled by daily light/dark cycles. Light falls on photoreceptive cells in the eye that directly connect to the brain’s master clock. Based on new research, the lighting industry is beginning to explore how lighting can be used to promote circadian health.
The LRC study is the first to measure personal circadian light exposure in office workers using a device calibrated to measure circadian-effective light. It is also the first to directly relate circadian-effective light measures to mood, stress, and sleep outcomes. Led by Mariana Figueiro, professor and director of the center’s Light and Health Program, the research team set out to explore the connection between light exposure and sleep, depression, and stress in office workers. The study included 109 participants at five office buildings managed by the U.S. General Services Administration (GSA).
“We are supporting this type of research so we can learn more about the connections between lighting and health,” noted Bryan Steverson of the GSA in an LRC press release. “The data from this research will help support our efforts in developing new lighting practices that can optimize health benefits for federal employees working in our federal buildings.”
Study participants each wore a Daysimeter, a research tool LRC developed to measure the amount of circadian stimulus (CS) they received along with their activity patterns. CS is a metric the LRC developed to express the effectiveness of light’s impact on the circadian system. It ranges from .1, the threshold for circadian system activation, to .7, which is response saturation.
The participants wore their Daysimeter for seven consecutive days during data collection periods in both the summer and winter months from 2014 to 2016. The LRC collected data on their sleep and mood sing five standardized questionnaires. Participants also kept a log of bedtimes and wake times, sleep latency, quality of sleep, and any naps taken.
The researchers found that office workers receiving a morning CS of at least .3 (electric lighting and/or daylight) showed greater circadian entrainment, were able to fall asleep more quickly at bedtime (an effect more pronounced in winter than summer), and experienced better-quality sleep than those receiving a morning CS of .15 or less. They also reported lower levels of stress with no seasonal variation. At bedtime, participants who received low CS lay in bed approximately 45 minutes before falling asleep.
While receiving high CS in the morning is hypothetically the most beneficial for entrainment, participants receiving high CS throughout the entire workday (8:00 a.m. to 5:00 p.m.) experienced better sleep quality and felt less depressed compared with those receiving low CS.
“Our study shows that exposure to high CS during the day, particularly in the morning, is associated with better overall sleep quality and mood scores than exposure to low CS,” Figueiro said in an LRC press release. “The present results are a first step toward promoting the adoption of new, more meaningful metrics for field research, providing new ways to measure and quantify circadian-effective light.”
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