title: Phase delaying the human circadian clock with blue-enriched polychromatic light.
abstract: The human circadian system is maximally sensitive to short-wavelength (blue) light. In a previous study we found no difference between the magnitude of phase advances produced by bright white versus bright blue-enriched light using light boxes in a practical protocol that could be used in the real world. Since the spectral sensitivity of the circadian system may vary with a circadian rhythm, we tested whether the results of our recent phase-advancing study hold true for phase delays. In a within-subjects counterbalanced design, this study tested whether bright blue-enriched polychromatic light (17000 K, 4000 lux) could produce larger phase delays than bright white light (4100 K, 5000 lux) of equal photon density (4.2x10(15) photons/cm(2)/sec). Healthy young subjects (n = 13) received a 2 h phase delaying light pulse before bedtime combined with a gradually delaying sleep/dark schedule on each of 4 consecutive treatment days. On the first treatment day the light pulse began 3 h after the dim light melatonin onset (DLMO). An 8 h sleep episode began at the end of the light pulse. Light treatment and the sleep schedule were delayed 2 h on each subsequent treatment day. A circadian phase assessment was conducted before and after the series of light treatment days to determine the time of the DLMO and DLMOff. Phase delays in the blue-enriched and white conditions were not significantly different (DLMO: -4.45+/-2.02 versus -4.48+/-1.97 h; DLMOff: -3.90+/-1.97 versus -4.35+/-2.39 h, respectively). These results indicate that at light levels commonly used for circadian phase shifting, blue-enriched polychromatic light is no more effective than the white polychromatic lamps of a lower correlated color temperature (CCT) for phase delaying the circadian clock.
authors.affiliation: Rush University Medical Center, Chicago, Illinois 60612, USA.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Smith
authors.forename: Charmane I
authors.initials: CI
authors.lastname: Eastman
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D005260:Female; D006801:Humans; D008027:Light; D008029:Lighting; D008297:Male; D008550:Melatonin / Q000097:blood; D018579:Patient Selection; D011930:Reaction Time; D012890:Sleep; D014851:Wakefulness; D055815:Young Adult
chemical_list: D008550:Melatonin