Do bright-light shock exposures during breaks reduce subjective sleepiness in night workers?


Night work has many harmful effects on the health, efficiency and safety of workers. This study evaluates the effects of bright-light exposure (BL) on subjective sleepiness during night work. Ninety night workers who have more than a year’s experience at a metallurgy production plant volunteered to participate in this clinical pilot study. Workers were divided into two groups and every group was exposed to either bright light (2500–3000 lux) or normal light (300 lux) during break times at night for two consecutive nights. Fifteen-minute breaks were initiated at 22.00 h (before starting work) 24.00 h, 02.00 h and 04.00 h. The range of subjective sleepiness was assessed by the Stanford Sleepiness Scale (SSS) at 23.00 h, 01.00 h, 03.00 h and 05.00 h. We used SPSS 11.5 for data analysis. The result demonstrated that there were significant differences in the rate of sleepiness between the two groups by paired t-test analysis (P < 0.001). These findings suggest that photic stimulation in industrial settings could increase adaptation to night work.

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Correspondence to Mohsen Zare.

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Karchani, M., Kakooei, H., Yazdi, Z. et al. Do bright-light shock exposures during breaks reduce subjective sleepiness in night workers?. Sleep Biol. Rhythms 9, 95–102 (2011).

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Key words

  • bright-light exposure
  • shift work
  • sleepiness
  • Stanford Sleepiness Scale