Late bedtimes stop teenagers’ body clocks from shifting earlier in response to morning bright light

Adolescents who experienced sleep restriction showed no advancement in their sleep schedule, while those with adequate sleep advanced by 2 hours.

• Sleep restriction involved delaying bedtimes by 4.5 hours and limiting sleep to 5.5 hours.
• Participants receiving evening light and sleep restriction did not shift their sleep schedule.
• In contrast, participants with consistent 10-hour sleep opportunities advanced their sleep schedule.
• Bright morning light exposure of 90 minutes (~6000 lux) was provided after waking.
• The results indicate that sleep saturation may facilitate earlier sleep timing compared to sleep restriction.

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