<p>The aim of this study was to investigate the effects of bright-light exposure immediately prior to sleep on the human urine metabolome. Eight young and healthy men were exposed to dim light (control condition) or bright-light (10000 lux) 3 hours before sleep (Bright-light condition: BL). Objective sleep quality was recorded by polysomnography, and subjective sleep quality was evaluated by the Oguri-Shirakawa-Azumi sleep inventory MA version (OSA-MA). Urine samples were collected after waking up under both the BL and control conditions. Polysomnographic analysis showed that sleep latency was significantly increased in BL compared to the control condition. OSA-MA score of refreshing was significantly lower in BL. Moreover, body temperature was significantly higher at times around sleep onset in BL (23:30, 0:00, and 0:30). Together, these results suggest that exposure to bright-light prior to sleep can alter sleep and circadian rhythms. According to analysis of the urine metabolome, the level of Allothreonine was significantly higher and the levels of N-acetylleucine, ornithine, 5-hydroxylysine, carnosine, and 4-amino-3-hydroxybutyric acid were significantly lower in BL (P < 0.05).