Efficacy of bright light and sleep/darkness scheduling in alleviating circadian maladaptation to night work

We tested the hypothesis that circadian adaptation to night work is best ac hieved by combining bright light during the night shift and scheduled sleep in darkness. Fifty-four subjects participated in a shift work simulation o f 4 day and 3 night shifts followed by a 38-h constant routine (CR). Subjec ts received 2,500 lux (Bright Light) or 150 lux (Room Light) during night s hifts and were scheduled to sleep (at home in darkened bedrooms) from 0800 to 1600 (Fixed Sleep) or ad libitum (Free Sleep). Dim light melatonin onset (DLMO) was measured before and after the night shifts. Both Fixed Sleep an d Bright Light conditions significantly phase delayed DLMO. Treatments comb ined additively, with light leading to larger phase shifts. Free Sleep subj ects who spontaneously adopted consistent sleep schedules adapted better th an those who did not. Neither properly timed bright light nor fixed sleep s chedules were consistently sufficient to shift the melatonin rhythm complet ely into the sleep episode. Scheduling of sleep/darkness should play a majo r role in prescriptions for overcoming shift work-related phase misalignmen t.