Night and rotating shift work schedules induce misalignment between the phase of the circadian pacemaker and the work/sleep schedule, leading to excessive fatigue at work and disrupted daytime sleep in night workers. Also, night work often begins after more extended wakefulness than daytime work. This combination leads to sleepiness, errors, and injuries on the night shift, as well as health problems. These effects are worse for older workers. While we have shown that treating young subjects with bright light and a fixed morning sleep schedule results in rapid circadian adaptation to night work, preliminary studies indicate that this strategy will be ineffective for older people, whose sleep is more sensitive to incomplete circadian adaptation to delayed sleep schedules. Given the increasing median age of the workforce, it is critical to develop shift work effective countermeasures for the older worker. We hypothesize that phase advancing the sleep episode and circadian rhythm will be a more effective strategy in older workers. We propose three testable hypotheses: that 1) older subjects who work 3 successive night shifts and sleep ad lib will suffer from misalignment between their work/sleep schedule and their circadian phase, disrupted daytime sleep, and degraded night shift performance relative to the day shift; 2) in older subjects who are scheduled to sleep in the morning after their night shifts, working 3 successive nights in bright light during the beginning of the night shift will improve alignment between the work/sleep cycle and the circadian melatonin rhythm compared to working 3 successive night shifts in standard room light, without the corresponding improvement in sleep and night shift performance that has been observed in young subjects; and, 3) in older subjects who are scheduled to sleep in the evening before their night shifts, working 3 successive nights in bright light during the late hours of the night shift will improve alignment between the work/sleep cycle and the circadian melatonin rhythm compared to working 3 successive night shifts in standard room light, with a corresponding improvement in sleep and night shift performance. We propose an experiment to evaluate the effects of two regimens combining bright light treatment and scheduled sleep on circadian melatonin rhythms, sleep, performance in older individuals in a laboratory simulation of night work. We propose to measure activity and light exposure with ambulatory devices, circadian phase using salivary melatonin levels, sleep via polysomnography, and performance by computerized tests. This work has major implications for the health and safety of older shift workers.