Fazlali, F.; Lazar, R.; Yahya, F.; Epple, C.; Spitschan, M.; Stefani, O.; Cajochen, C.

Light exposure at night can suppress melatonin production and increase alertness, primarily through the action of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). This study investigated whether cone photoreceptors also influence melatonin suppression and subjective alertness using non-visual metameric light emitted from a display. Forty-eight participants with normal trichromatic vision were exposed to three lighting conditions: a baseline (9 lxmEDI), constant background (149 lxmEDI), and cone-modulated flickering light targeting different cone combinations and post-receptoral channels (149 lxmEDI) for 2 hours after their habitual bedtime. Salivary melatonin levels and subjective alertness were measured throughout a 9-h protocol. Bayesian analysis showed that cone-modulated flickering light did not significantly affect melatonin suppression or alertness, providing evidence against the hypothesis that cone photoreceptors contribute to these non-visual effects of light. In conclusion, our results suggest cone photoreceptors do not play a measurable role in light\'s effects on melatonin suppression and subjective alertness at night.