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Abstract:
Exposure to short-wavelength (?480 nm) light in the evening can acutely suppress melatonin, induce circadian phase delays, and affect alertness and sleep. These effects are mediated via a pathway connecting the retina and the central circadian pacemaker in the suprachiasmatic nuclei. Melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) are thought to be the primary drivers of this pathway. Much less is known about the contribution of the colour-sensitive cones. Still, especially light changing along the blue-yellow dimension of colour vision could have a relevant contribution in addition to ipRGCs. Thus, using calibrated silent-substitution changes in light colour along the blue-yellow axis, we investigated in a Registered Report whether mechanisms of colour vision affect the human circadian timing system and sleep. In a within-subjects laboratory protocol, 16 participants (8 women, 18-35 years old) were exposed to three different light scenarios for one hour starting 30 min after habitual bedtime: a control condition (“background”, 93.5 lux), intermittently flickering (1 Hz, 30 seconds on/off, against background light) yellow-bright light, and intermittently flickering blue-dim light. Importantly, there was no difference in melanopsin excitation (163 lux melanopic EDI) between the conditions. Bayesian statistics did not yield conclusive evidence for differences between the three lighting conditions regarding phase delays, melatonin suppression, sleepiness, psychomotor vigilance, or sleep. Thus, this study found no evidence that evening light changing along the blue-yellow dimension under typical light levels has a major impact on human circadian melatonin secretion, alertness, and sleep. The main effect seems to be mediated via melanopsin-containing ipRGCs.
