SleepSep 1, 1994

Dark Goggles and Bright Light Help Adjust the Body Clock for Night-Shift Workers

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 31, 2026

Abstract

Bright light exposure of about 5,000 lux significantly influenced circadian rhythm phase shifts in temperature.

Both bright light and dark goggles were significant in producing phase shifts of the circadian rhythm.
The combination of bright light and goggles was the most effective for realigning circadian rhythms.
Dim light exposure and no goggles resulted in the least effective phase shifts.
Subjects without goggles only experienced phase advances, indicating goggles are necessary for phase delays.
Larger phase shifts in temperature rhythm were associated with improved subjective daytime sleep, reduced fatigue, and enhanced mood.

Simplified

We compared the contributions of bright light during the night shift and dark goggles during daylight for phase shifting the circadian rhythm of temperature to realign with a 12-hour shift of sleep. After 10 baseline days there were 8 night-work/day-sleep days. Temperature was continuously recorded from 50 subjects. There were four groups in a 2 x 2 design: light (bright, dim), goggles (yes, no). Subjects were exposed to bright light (about 5,000 lux) for 6 hours on the first 2 night shifts. Dim light was < 500 lux. Both bright light and goggles were significant factors for producing circadian rhythm phase shifts. The combination of bright light plus goggles was the most effective, whereas the combination of dim light and no goggles was the least effective. The temperature rhythm either phase advanced or phase delayed when it aligned with daytime sleep. However, when subjects did not have goggles only phase advances occurred. Goggles were necessary for producing phase delays. The most likely explanation is that daylight during the travel-home window after a night shift inhibits phase-delay shifts, and goggles can prevent this inhibition. Larger temperature-rhythm phase shifts were associated with better subjective daytime sleep, less subjective fatigue and better mood.

Dark Goggles and Bright Light Help Adjust the Body Clock for Night-Shift Workers

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