title: Controlling light-dark exposure patterns rather than sleep schedules determines circadian phase.
abstract: OBJECTIVE
  To examine, in a field study circadian phase changes associated with two different light-dark exposures patterns, one that was congruent with a phase advanced sleep schedule and one that was incongruent with an advanced schedule.
  
  
  METHODS
  Twenty-one adults (mean age±standard deviation=22.5±3.9 years; 11 women) participated in the 12day study. After a five-day baseline period, participants were all given individualized, fixed, 90-minute advanced sleep schedules for one week. Participants were randomly assigned to one of two groups, an advance group with a light-dark exposure prescription designed to advance circadian phase or a delay group with light-dark exposure prescription designed to delay circadian phase. The advance group received two morning hours of short-wavelength (blue) light (λmax ≈ 476±1 nm, full-width-half-maximum ≈20 nm) exposure and three evening hours of light restriction (orange-filtered light, λ<525 nm=0). The delay group received blue light for three hours in the evening and light restriction for two hours in the morning. Participants led their normal lives while wearing a calibrated wrist-worn light exposure and activity monitor.
  
  
  RESULTS
  After seven days on the 90-minute advanced sleep schedule, circadian phase advanced 132±19 minutes for the advance group and delayed 59±7.5 minutes for the delay group.
  
  
  CONCLUSIONS
  Controlling the light-dark exposure pattern shifts circadian phase in the expected direction irrespective of the fixed advanced sleep schedule.
authors.affiliation: Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Appleman
authors.forename: Mariana G
authors.initials: MG
authors.lastname: Figueiro
authors.forename: Mark S
authors.initials: MS
authors.lastname: Rea
mesh_terms: D056044:Actigraphy; D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008027:Light; D008029:Lighting / Q000379:methods*; D008297:Male; D008550:Melatonin / Q000097:blood; D017440:Photoperiod; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D055815:Young Adult
chemical_list: D008550:Melatonin