We administered daily morning bright light exposure in two separate periods to a demented aged subject in a nursing home and analyzed the sleep pattern changes from the sleep diary over 6 months. In the first light exposure period, the ratio of sleep time in night hours increased and maintained a higher value throughout the period than the previous baseline. After stopping the light exposure, the sleep pattern of the subject deteriorated. Resuming the light exposure reproduced similar sleep pattern changes. These results suggest that morning bright light exposure provides a better environment for aged persons to maintain a regular sleep-wake pattern.