The disturbed sleep seen in nursing home residents may be due to changes in circadian rhythms. Human circadian rhythms are biological cycles of about 24 hours that include sleep/wake, body temperature, and melatonin secretion cycles. A second reason for sleep disturbances in this population may be decreased exposure to bright light. Bright light (≥ 2,000 lux) appears to be one of the most powerful synchronizers of circadian rhythms, directly influencing melatonin secretion, sleep/wake patterns, and other circadian rhythms.