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Phase delaying the human circadian clock with blue-enriched polychromatic light
Mark R Smith1, Charmane I Eastman
1Rush University Medical Center, Chicago, Illinois 60612, USA.
Chronobiology International
|May 16, 2009
Summary
Bright blue-enriched light is no more effective than white light for delaying the human circadian clock. This study found no significant difference in phase delays between blue-enriched and white light conditions when used for circadian rhythm adjustment.
Area of Science:
- Chronobiology
- Human Physiology
- Light Therapy
Background:
- The human circadian system shows peak sensitivity to short-wavelength (blue) light.
- Previous research indicated no difference in phase advances between white and blue-enriched light.
- Spectral sensitivity of the circadian system may fluctuate, necessitating investigation into phase delays.
Purpose of the Study:
- To determine if bright blue-enriched light causes greater phase delays than bright white light.
- To assess the efficacy of blue-enriched light for circadian rhythm phase shifting.
- To compare the effects of different light spectra on circadian phase adjustment.
Main Methods:
- A within-subjects, counterbalanced design was employed with 13 healthy young subjects.
- Subjects received a 2-hour phase-delaying light pulse daily for 4 days.
- Light treatments involved either blue-enriched (17000 K) or white (4100 K) polychromatic light at equal photon density, alongside a gradually delaying sleep/dark schedule.
Main Results:
- Phase delays in the blue-enriched light condition were -4.45+/-2.02 hours (DLMO) and -3.90+/-1.97 hours (DLMOff).
- Phase delays in the white light condition were -4.48+/-1.97 hours (DLMO) and -4.35+/-2.39 hours (DLMOff).
- No statistically significant difference was observed between the blue-enriched and white light conditions for either DLMO or DLMOff phase delays.
Conclusions:
- Blue-enriched polychromatic light is not more effective than white polychromatic light of lower correlated color temperature (CCT) for phase delaying the human circadian clock.
- At light intensities commonly used for circadian phase shifting, the spectral composition (blue-enriched vs. white) does not yield differential phase delay effects.
- These findings suggest that for practical applications of circadian phase delay, the tested white light is as effective as blue-enriched light.
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