Effects of bright light pre-exposure on sleep onset process

This study investigated the effects on the sleep onset process of enhanced cerebral cortex activity caused by bright light pre-exposure. Seven healthy young adults were exposed for 40 min before sleep onset, 2500 Ix of bright light and 10 I:x of dim light. Other factors that affect sleep onset (e.g. circadian phase) were experimentally controlled. Five stages of hypnagogic electroencephalogram (EEG) were scored. The latency of each EEG stage was longer at bright light than at dim light conditions, suggesting that activation of brain activity by bright light pre-exposure strongly regulates the sleep onset process.