Modeling the influence of nighttime light on melatonin suppression in humans: Milestones and perspectives

This review presents the main metrics developed so far to correlate physical properties of light and its effects on melatonin suppression. Melatonin is a hormone secreted at night and its production is suppressed by exposure to light. In this context, the negative effects of lighting at night and high exposure to light raise the need for a better quantification of these impacts on health. Different light action spectroscopy methodologies have been recently used to characterize the circadian response mediated by melatonin in humans, but there is so far no consensus on a main validated model. While complementary studies are still necessary to reach such an ideal model, here we analyze and compare the results of works that developed and tested metrics based on the absorption curves of human melanopsin, rods and cones, and on the dynamics of melatonin suppression in different light regimes. These studies reveal how the spectral composition, irradiance and temporality of light modulate the function of human melatonin. We present milestones in this research field, together with discussion on the advances, limitations and perspectives of application for distinct available models. Applied to different contexts, this knowledge can bring favorable changes to health in environmental lighting projects, production of ophthalmic lenses, screens, filters, films, and other optical devices.