Neuroscience Letters (2003)
February 11, 2003

Victoria L. Warman, Derk-Jan Dijk, Guy R. Warman, Josephine Arendt, Debra J. Skene

Neuroscience Letters 342 (2003) 37-40


The photoreceptor(s) responsible for photoresetting of the human circadian system have not been identified. The aim of the present study was to assess the ability of short wavelength light to alter the timing of circadian rhythms. Eleven male subjects were studied in 15 4-day trials with a single 4 h light pulse administered on day 3, immediately after habitual wake time. The magnitude of the phase shifts in the melonin acrophase and offset were similar after white (4300 mW/cm2) and short wavelength (28 mW/cm2) light exposure even though the white light pulse contained 185-fold more photons than the short wavelength light. This finding suggests short wavelength sensitivity of the photoreceptors mediating synchronization of human circadian rhythms.

Conclusion: In conclusion, the current data demonstrate that a very low intensity short wavelength light pulse (8 lux) is able to phase advance the human circadian system to a similar magnitude as a bright white light pulse (12000 lux) containing 185-fold more photons. This finding suggests that the human circadian system is particularly sensitive to the phase advancing effects of short wavelength light and that the visual photopic system is not primarily involved. Our finding supports the recent human studies investigating the spectral sensitivity of light-induced melatonin suppression. © 2003 Elsevier Science Ireland Ltd. All rights reserved.