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Updated: Jun 9, 2026
Collecting Sleep, Circadian, Fatigue, and Performance Data in Complex Operational Environments
Published on: August 8, 2019
The effect of bright light on sleepiness among rapid-rotating 12-hour shift workers
Khosro Sadeghniiat-Haghighi1, Zohreh Yazdi, Hassan Jahanihashemi
1Baharloo Hospital, Occupational Medicine Department, Tehran University of Medical Science, Tehran, Iran.
Objective:
About 20% of workers in industrialized countries are shift workers and more than half of them work on night or rotating shifts. Most night workers complain of sleepiness due to lack of adjustment of the circadian rhythm. In simulated night-work experiments, scheduled exposure to bright light has been shown to reduce these complaints. Our study assessed the effects of bright light exposure on sleepiness during night work in an industrial setting.
Methods:
In a cross-over design, 94 workers at a ceramic factory were exposed to either bright (2500 lux) or normal light (300 lux) during breaks on night shifts. We initiated 20-minute breaks between 24.00 and 02.00 hours. Sleepiness ratings were determined using the Stanford Sleepiness Scale at 22.00, 24.00, 02.00 and 04.00 hours.
Results:
Under normal light conditions, sleepiness peaked at 02:00 hours. A significant reduction (22% compared to normal light conditions) in sleepiness was observed after workers were exposed to bright light.
Conclusion:
Exposure to bright light may be effective in reducing sleepiness among night workers.
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