Many older people complain of sleep maintenance insomnia and waking prematurely. This occurs even in healthy, non-depressed older people without sleep complaints or circadian rhythm abnormalities. We found an age-related change in the circadian phases over which the latter part of sleep remains consolidated and an age-related increase in the variability of entrained circadian phase. We hypothesize that these age related circadian changes may account for much of the high prevalence of disrupted sleep and early waking in older people. This implies that maintaining an ideal timing between circadian phase and sleep is crucial for sleep consolidation in older people. Adjustment of this relationship can be achieved by evening light exposure, although the duration and intensity required to sustain an effect can make compliance difficult. Our recent studies have revealed that the human circadian system is more responsive to short than to longer wavelength light. This suggests that light treatments for achieving an optimum phase relationship between sleep and circadian rhythms may be achieved using shorter durations and/or lower intensities if the light is enriched in the shorter wavelengths. We propose comparing a light treatment regimen using a newly available blue-enriched light source with the same treatment using standard light sources. We will assess the change in phase relationship between the circadian melatonin rhythm and sleep timing, and the change in subjective & objective sleep quality on treatment nights and for several nights thereafter. Sleep disruption is an important cause of diminished quality of life in otherwise healthy older people, often leading to an overuse of sleep medications with unfortunate physiological and psychological side effects. Greater understanding of the mechanisms causing age-related sleep disruption, and careful evaluation of this new treatment will be important in developing practical, non-pharmacologic treatment methods, and offers promise for improving the health and well-being of older people.