Appropriately timed exposure to bright light has been shown to phase shift the circadian rhythm and alleviate associated sleeping difficulties. This study evaluated the effectiveness of a newly developed Re-Timer portable light device for phase delaying the circadian rhythm.


Participants included 12 healthy, good sleepers (M = 32.3 years, SD = 12.5, male = 5). A repeated measures counterbalanced design was used to assess circadian phase delay following the use of either the re-timer or no device on two consecutive evenings. Outcome measures included dim light melatonin onset (DLMO), subjective sleepiness, and adverse effects of the Re-Timer. Analyses revealed a significant phase delay of DLMO following use of the re-timer (M = 46 min, SD = 76 min) on two consecutive evenings when compared to no light control (M = 3 min, SD = 81 min; p = .016).


There was a trend for evening subjective sleepiness to decrease after using the Re-Timer compared to no light control, however this trend was not statistically significant. The Re-Timer device is an effective method of delaying the circadian rhythm in good sleepers.

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