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Circadian phase delay using the newly developed re-timer portable light device


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. Adverse effects of the re-timer were headache, eye irritation, and light bothersome to eyes, however these were not severe and treatment was not requested or required. The re-timer device is an effective method of delaying the circadian rhythm in good sleepers.

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Correspondence to Nicole Lovato.

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Conflict of interest

LL is a stock shareholder in the company RE-Time, PTY. LTD and was involved in the development of the re-timer device. NL has no conflict of interest to disclose. RE-Time, PTY. LTD provided the re-timer devices used in this study.

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Lovato, N., Lack, L. Circadian phase delay using the newly developed re-timer portable light device. Sleep Biol. Rhythms 14, 157–164 (2016).

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  • Bright light
  • Circadian rhythms
  • Endogenous melatonin
  • Sleep
  • Portable light device
  • Re-timer