We measured the illuminance exposure for 3 days in winter of a convenience sample of 44 elderly people certified as requiring support in Japan's Hokuriku region. We calculated the illuminance ratio per minute during activity and while in bed and analyzed the relationship between illuminance, subjective sleep quality, and psychosomatic health. There was a significant negative correlation between illuminance and 15-item Geriatric Depression Scale scores. Multiple regression analysis indicated that depression scores were significantly related to age, level of required support, and illuminance. The findings suggest that environments without light and dark cycles increase depression scores in frail elderly people.