Objective

Shorter wavelength light has been shown to be more effective than longer wavelengths in suppressing nocturnal melatonin and phase-delaying the melatonin rhythm. In the present study, different wavelengths of light were evaluated for their capacity to phase advance the saliva melatonin rhythm.

Method

Light was administered via a portable light source comprising two light-emitting diodes per eye, with the irradiance of each diode set at 65 lW/cm2. Forty-two volunteers participated in up to six conditions resulting in 15 per condition. For the active light conditions, a 2-hour light pulse was administered from 06.00 on two consecutive mornings. Half-hourly saliva samples were collected on the evening prior to the first light pulse and the evening following the second light pulse.

Conclusion

The shorter wavelengths of 470, 495 and 525 nm showed the greatest melatonin onset advances ranging from approximately 40 to 65 minutes while the longer wavelengths produced no significant phase advance.

These results strengthen earlier findings that the human circadian system is more sensitive to the short wavelengths of light than the longer wavelengths.