Late evening room light and sleep restriction reduces the ability of bright morning light to phase advance adolescents' circadian clocks.

Adolescents experience chronic partial sleep deprivation primarily due to late bedtimes and early school start times. Late bedtimes are partly driven by late (delayed) circadian rhythms. Morning bright light (MBL) advances (shifts earlier) circadian rhythms; however, extending evening light by staying awake late may delay the circadian clock and limit effectiveness of MBL. We investigated how increasing durations of late evening light coupled with sleep restriction affects the advancing ability of MBL in adolescents (14–17 years). Bedtime was delayed by 0 h (n = 11), 1.5 h (n = 9), 3 h (n = 12), or 4.5 h (n = 8), resulting in sleep opportunities of 10 h, 8.5 h, 7 h, or 5.5 h. Participants received 90 min of MBL on 3 consecutive mornings while the sleep/dark episode gradually shifted earlier. Participants in the 10-h and 8.5-h sleep groups phase advanced by 2.0 ± 1.1 h and 0.5 ± 0.6 h. Participants in the 7-h and 5.5-h sleep groups delayed by 0.8 ± 1.1 h and 2.6 ± 1.2 h. Thus, advance shifts from MBL were reduced in a step-wise manner with increasing duration of evening light and decreasing sleep opportunity, ultimately producing phase delays. These results suggest that MBL efficacy is reduced in adolescents with restricted sleep opportunities associated with late bedtimes and early school start times. These factors need to be considered in circadian-based treatment approaches.