It is generally acknowledged that almost three-quarters of the 20 million shift workers in the United States suffer from a variety of symptoms associated with the maladjustment of their circadian rhythms to an ever- changing work schedule. The cost of shift work due to accidents, loss of productivity and increased health care demands is staggering. Recently, the aggregate social cost was estimated at approximately 70 billion dollars annually. Despite the magnitude of the problem, traditional approaches to reducing the impact of shift work have been largely unsuccessful. The traditional use of hypnotics to treat sleep disturbance in shift work populations is complicated by a number of factors, the most problematic of which are hangover effects on waking function and the potential for abuse. Attempts to implement behavioral strategies that address more closely the etiology of the disturbance, have been largely unsuccessful due to compliance problems. In contrast, the use of bright light offers a safe and viable alternative. The approach offers rapid action without the drawbacks associated with pharmacological interventions. There is substantial evidence that exposure to bright light is effective in modifying both the phase and the amplitude of circadian rhythms, which in turn, can improve sleep quality and waking function. This knowledge has already been applied successfully in clinical circadian disorders, but surprisingly, it has not been used to address the problems associated with circadian adaptation to shift work. Because night shift workers are awake, and thus available, to receive light during intervals in which the most robust physiological effects have been demonstrated, they constitute an ideal population for such an approach. The use of timed bright light exposure to shift circadian phase is likely to alleviate shift work related sleep disturbance. Similarly, enhancement of circadian amplitude has been shown to improve on-duty task performance and efficiency. The research proposed here will be the first to evaluate and compare three approaches using timed exposure to bright light to achieve rapid adjustment of the circadian system to shift work. The study will separately examine the phase shifting, amplitude enhancing and combined effects of bright light on circadian adaptation and performance. Subjects working 3 simulated night shifts will receive either a single 4- hour pulse of bright light on the first night of work, increased ambient illumination throughout the 3 night shifts, or a combination of both lighting strategies across the work shifts. Rates of physiological and behavioral adaptation will be compared across treatment groups and with a control group receiving no treatment. It is expected that these important and necessary laboratory-based, simulated night shift studies will form the basis for subsequent investigations to evaluate the efficacy of such interventions in applied settings.