Human melatonin regulation is not mediated by the three cone photopic visual system.

The aim of this study was to test if the three cone photopic visual system is the primary ocular photoreceptor input for human circadian regulation by determining the effects of different wavelengths on light-induced melatonin suppression. Healthy subjects with stable sleeping patterns (wake-up time 7:30 AM ± 12 min) and normal color vision were exposed at night to full-field 505 nm or 555 nm monochromatic stimuli or darkness for 90 min. Plasma collected before and after exposures was quantified for melatonin. Subjects exposed to 10 irradiances at 505 nm showed no significant differences across mean pre-exposure melatonin values (F=0.505). A sigmoidal fluence-response curve fitted to the melatonin suppression data (R2=0.97) indicated that 9.34 × 1012 photons/cm2/sec induced a half-saturation response (ED50) while 6.84 × 1013 photons/cm2/sec induced a saturation melatonin suppression response. Further, a dose of 4.19 × 1013 photon/cm2/sec at 505 nm was significantly stronger (P < 0.01) than an equal photon...