Abstract

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.