title: Individually tailored light intervention through closed eyelids to promote circadian alignment and sleep health.
abstract: BACKGROUND
  Light is most effective at changing the timing of the circadian clock when applied close to the core body temperature minimum. The present study investigated, in a home setting, if individually tailored light treatment using flashing blue light delivered through closed eyelids during the early part of the sleep period delayed circadian phase and sleep in a population of healthy older adults and in those suffering from early awakening insomnia.
  
  
  METHODS
  Twenty-eight participants (9 early awakening insomniacs) completed an 8-week, within-subjects study. Twice, participants collected data during two baseline weeks and one intervention week. During the intervention week, participants wore a flashing blue (active) or a flashing red (control) light mask during sleep. Light was expected to delay circadian phase. Saliva samples for dim light melatonin onset (DLMO) were collected at the end of each baseline and intervention week. Wrist actigraphy and Daysimeter, a calibrated light and activity meter, data were collected during the entire study.
  
  
  RESULTS
  Compared to baseline, flashing blue light, but not flashing red light, significantly (p<0.05) delayed DLMO. The mean ± standard deviation phase shift (minutes) was 0:06 ± 0:30 for the flashing red light and 0:34 ± 0:30 for the flashing blue light. Compared to Day 1, sleep start times were significantly delayed (by approximately 46 minutes) at Day 7 after the flashing blue light. The light intervention did not affect sleep efficiency.
  
  
  CONCLUSIONS
  The present study demonstrated the feasibility of using light through closed eyelids during sleep for promoting circadian alignment and sleep health.
authors.affiliation: Lighting Research Center, Rensselaer Polytechnic Institute, Troy, New York.
authors.forename: Mariana G
authors.initials: MG
authors.lastname: Figueiro
keywords: Circadian phase; dim light melatonin onset; early awakening insomniacs; flashing blue light; light through closed eyelids; sleep