title: The effects of chronotype, sleep schedule and light/dark pattern exposures on circadian phase.
abstract: BACKGROUND
  Chronotype characterizes individual differences in sleep/wake rhythm timing, which can also impact light exposure patterns. The present study investigated whether early and late chronotypes respond differently to controlled advancing and delaying light exposure patterns while on a fixed, advanced sleep/wake schedule.
  
  
  METHODS
  In a mixed design, 23 participants (11 late chronotypes and 12 early chronotypes) completed a 2-week, advanced sleep/wake protocol twice, once with an advancing light exposure pattern and once with a delaying light exposure pattern. In the advancing light exposure pattern, the participants received short-wavelength light in the morning and short-wavelength-restricting orange-tinted glasses in the evening. In the delaying light exposure pattern, participants received short-wavelength-restricting orange-tinted glasses in the morning and short-wavelength light in the evening. Light/dark exposures were measured with the Daysimeter. Salivary dim light melatonin onset (DLMO) was also measured.
  
  
  RESULTS
  Compared to the baseline week, DLMO was significantly delayed after the delaying light intervention and significantly advanced after the advancing light intervention in both groups. There was no significant difference in how the two chronotype groups responded to the light intervention.
  
  
  CONCLUSIONS
  The present results demonstrate that circadian phase changes resulting from light interventions are consistent with those predicted by previously published phase response curves (PRCs) for both early and late chronotypes.
authors.affiliation: Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA. Electronic address: figuem@rpi.edu.
authors.forename: Mariana G
authors.initials: MG
authors.lastname: Figueiro
authors.affiliation: Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Plitnick
authors.affiliation: Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Rea
mesh_terms: D000293:Adolescent; D000328:Adult; D021081:Chronobiology Disorders / Q000628:therapy*; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008550:Melatonin / Q000032:analysis* / Q000502:physiology; D008875:Middle Aged; D010789:Phototherapy / Q000379:methods*; D012463:Saliva / Q000737:chemistry; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D008550:Melatonin
keywords: Chronotype; Circadian phase; Dim light melatonin onset; Light; Light/dark exposure; Phase response curve