Effects of calibrated blue-yellow (-S+) changes in light on the human circadian clock

Abstract

Evening exposure to short-wavelength light can acutely affect the circadian clock located in the suprachiasmatic nuclei, sleep, and alertness. The intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin are thought to be the primary drivers of these effects. Much less is known about the contribution of the colour-sensitive cones. Using calibrated silent-substitution changes in light colour along the blue-yellow axis, we investigated whether mechanisms of colour vision affect the human circadian system and sleep. In a 32.5-h repeated within-subjects protocol, 16 healthy participants (8 women, 18-35 years old) were exposed to three different light scenarios for 1 h starting 30 min after habitual bedtime: a control condition ("background", 93.5 photopic lux), intermittently flickering yellow-bright light (1 Hz, 30s on-off, 123.5 photopic lux), and intermittently flickering blue-dim light (1 Hz, 30s on-off; 67.0 photopic lux). Importantly, there was no difference in melanopsin excitation (163.2{+/-}2.1 lux melanopic EDI) between the three lighting conditions, allowing us to determine the unique contribution of the blue-yellow colour system. Our analyses did not yield conclusive evidence for differences between the three lighting conditions regarding circadian melatonin phase delays, melatonin suppression, subjective sleepiness, psychomotor vigilance, or sleep. Thus, in this study, we found no evidence that evening light changing along the blue-yellow dimension under moderate light levels typical for room illumination has a major impact on the human circadian clock or sleep. Our work underscores the previously demonstrated primary role of melanopsin-containing ipRGCs in mediating these effects.