Left in the dark Wavelength-dependent post-illumination effects on human physiology and behavior

The non-image forming effects of environmental light are critically mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) that are characterized by their expression of melanopsin, which is a photopigment that is maximally responsive to light in the blue part of the spectrum. The ipRGC-mediated effects of light can typically endure far beyond light offset, with widespread functional consequences, including changes in various aspects of human sleep. The present thesis investigated such sleep-related post-illumination effects in the context of physiology and behavior. In chapter 2 and 3, we presented a post-illumination pupil response (PIPR) after blue light assessment method that yields a robust and feasible estimate of the functionality of an individual’s intrinsic melanopsin-based phototransduction circuitry. In chapter 4, we showed that the PIPR after blue light was more pronounced in individuals with a later sleep timing. Following red light, sleep propensity is promoted, as indicated by our physiological and behavioral findings in chapter 5. Chapter 6 added to chapter 2 and 5 indicating that task demands and mental effort should be taken into account in order to correctly interpret changes in physiological and behavioral reflections of the central and autonomic nervous system. It appears timely to consider large-scale follow-up studies to contribute to the multivariate fingerprint of the non-image forming effects of light on human physiology and behavior and to further evaluate the clinical application of light therapy in the treatment of sleep disorders.