Late bedtimes prevent circadian phase advances to morning bright light in adolescents.

We examined phase shifts to bright morning light when sleep was restricted by delaying bedtimes. Adolescents (n = 6) had 10-h sleep/dark opportunities for 6 days. For the next 2 days, half were put to bed 4.5 h later and then allowed to sleep for 5.5 h (evening room light + sleep restriction). The others continued the 10-h sleep opportunities (sleep satiation). Then, sleep schedules were gradually shifted earlier and participants received bright light (90 min, ~6000 lux) after waking for 3 days. As expected, sleep satiation participants advanced (~2 h). Evening room light + sleep restriction participants did not shift or delayed by 2-4 h. Abbreviations: DLMO: dim light melatonin onset.