Abstract
Background
By affecting the internal timing mechanisms of the brain, light regulates human physiology
and behavior, perhaps most notably the sleep–wake cycle. Humans spend over 90% of
their waking hours indoors, yet light in the built environment is not designed to
affect circadian rhythms.
Objective
Using a device calibrated to measure light that is effective for the circadian system
(circadian-effective light), collect personal light exposures in office workers and
relate them to their sleep and mood.
Setting
The research was conducted in 5 buildings managed by the US General Services Administration.
Participants
This study recruited 109 participants (69 females), of whom 81 (54 females) participated
in both winter and summer.
Measurements
Self-reported measures of mood and sleep, and objective measures of circadian-effective
light and activity rhythms were collected for 7 consecutive days.
Results
Compared to office workers receiving low levels of circadian-effective light in the
morning, receiving high levels in the morning is associated with reduced sleep onset
latency (especially in winter), increased phasor magnitudes (a measure of circadian
entrainment), and increased sleep quality. High levels of circadian-effective light
during the entire day are also associated with increased phasor magnitudes, reduced
depression, and increased sleep quality.
Conclusions
The present study is the first to measure personal light exposures in office workers
using a calibrated device that measures circadian-effective light and relate those
light measures to mood, stress, and sleep. The study's results underscore the importance
of daytime light exposures for sleep health.
Keywords
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Article info
Publication history
Published online: April 23, 2017
Accepted:
March 15,
2017
Received in revised form:
March 9,
2017
Received:
November 7,
2016
Identification
Copyright
© 2017 National Sleep Foundation. Published by Elsevier Inc. All rights reserved.
