Abstract
Environmental light intensity (irradiance) is a powerful regulator of physiology and behaviour. A stable neuronal representation of light intensity is grounded in a specialised retinal output channel, found in humans and other mammals, and arising from intrinsically photosensitive retinal ganglion cells (ipRGCs). These are a rare class of retinal ganglion cells with autonomous sensitivity to light, thanks to their expression of the photopigment melanopsin. Melanopsin photoreception is optimised to encode low-frequency changes in the light environment and, as a result, extends the temporal and spatial range over which light is detected by the retina. ipRGCs innervate many brain areas, and this allows melanopsin light responses to be used for diverse purposes, ranging from the synchronization of the circadian clock with the solar day to light's regulation of mood, alertness, and neuroendocrine and cognitive functions. There is now also abundant evidence that ipRGCs also make an important contribution to the processes of perceptual vision, via their projection to the visual thalamus. Here I will discuss ongoing research exploring how melanopsin extends the spatial and temporal range over which light is detected by the retina, and the role this plays in augmenting the detection of patterns in brightness.