Effects of bright light shock on sleepiness and adaptation among night workers of a hospital in Iran

Background: Night work has many harmful effects on health, efficiency, and industrial safety of workers. Night workers often complained of sleepiness, decrease of performance, and sleep disorder due to the lack of circadian influence that fully encourages night orientation. Objective: This research was conducted in an industrial environment and it accessed the effects of bright-light (BL) exposure on sleepiness during night work. Materials and Methods: This is an interventional study with a cross-over design. A total of 140 night workers with an experience of >1 year at a hospital participated voluntarily in this study. The night workers were divided into two groups, and both groups were exposed to either BL (3000-3500 lux) or normal light (NL) (400 lux) during break times at night work for two consecutive nights. Results: The 15-minute breaks were initiated at 22:00 (before starting work), 24:00, 2:00, and 4:00 h. The range of sleepiness was assessed by the Karolinska Sleepiness Scale (KSS) at 23:00, 1:00, 3:00, and 5:00 h. We used SPSS16 software for data analysis. The results obtained using the paired t-test analysis (P < 0.000) demonstrated that there were significant differences in the rate of sleepiness between the two groups (case and control). Conclusion: The findings of the present study have also demonstrated the feasibility and benefits of photic stimulation in industrial settings which increased the adaptation to night work.