Abstract:The suppression of melatonin by bright light is probably mediated by the suprachiasmatic nucleus (SCN) in humans. In animals, SCN cells have broad visual receptive fields, suggesting that peripheral bright light could be effective for melatonin suppression. Twelve healthy subjects were subjected to 1000 lux illumination for 2 hr from 0100 to 0300 on two occasions: once lighting the central visual field 5° from the center of gaze and once lighting the peripheral visual field 60° lateral to the direction of gaze. Six subjects were observed on a third occasion in dim light. The three conditions differed significantly, with less melatonin secreted in 1000 lux, but melatonin levels with central and peripheral illumination did not differ. This suggests that phototherapy using bright light in the visual periphery may be effectiv