The effect of bright light on physiological circadian rhythms and subjective alertness of shift work nurses in Iran.

In this study, the effects of bright light (BL) on the rhythms in body temperature, plasma melatonin, plasma cortisol and subjective alertness, in 34 shift work nurses at a university hospital were assessed. They were exposed to very BL (4,500 lx) during 2 breaks (21:15-22:00 and 3:15-4:00) or dim light (300 lx). The subjects were studied under 24 h of realistic conditions during which their plasma cortisol and melatonin were measured at 3-h intervals; their body temperature was also measured during and after night shift work.