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Note: This study was a non-clinical consumer trial and has not been published in a scientific journal or peer-reviewed.


We investigated the ability of green light to advance sleep onset to an earlier time and increase sleep duration. The 24 participants were asked to nominate their current sub-optimal sleep–wake times and their preferred earlier or ideal sleep–wake times. A custom schedule was prepared for participants detailing the times to wear Re-Timer.


During the treatment week participants were asked to use the green light device for 50 minutes each 24-hour period for 7 days. All participants used the device in the morning shortly after waking (M = 8.42 am, SD = 2.23 hours). Wake-up times and exposure to green light were gradually advanced by an average of 8 minutes each morning, starting from each participant’s usual wake-up time. The choice of bedtime and wake-up times across the week were self-selected. Participants were asked to use the device for only 50 minutes at the prescribed time. After waking, all participants followed their usual morning routine while wearing the Re-Timer device. Participants recorded their sleep–wake routine during the treatment week in a sleep diary. The study was carried out in winter with morning light levels


Baseline data provided by participants prior to the trial showed the average sleep onset time was 1.47 (SD = 82 minutes). The average preferred sleep onset time participants wanted to achieve was 23.00 (SD = 56 minutes). This would be an average advance in sleep onset of 2 hours and 47 minutes, a significant change in the circadian clock. 92% (n = 22) achieved a movement towards their preferred sleep onset time; 8% did not realize any movement in their sleep onset time.

An average advance of 2 hours and 30 minutes was achieved across the sample (n = 24).

For green light to be considered an effective treatment option, duration of sleep should either be constant or increase as sleep onset time advances. Reduced sleep duration would result only in sleep debt.

Average sleep duration before the study was 7.1 hours (SD = 1.4 hours). On the 7th day of use, average sleep duration of participants was 7.8 hours (SD = 1.92 hours), an increase over the baseline measure by 0.7 hours (42 minutes).

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