In addition to supporting visual perception, light powerfully modulates mammalian physiology and behaviour via a non-image forming (NIF) system, comprising retinal projections to the hypothalamus and other subcortical visual centres. In contrast to the highly studied SCN, the mechanisms regulating other, more acute NIF responses remain sparsely investigated, as do the sensory properties of other retinorecipient hypothalamic regions. Using transgenic mouse strains and lighting conditions designed to selectively differ in brightness for specific photoreceptor classes, we show a key role for cone-derived colour signals in mediating light avoidance and acute light-induced suppression of rodent behaviour (Chapter 2). Specifically, we show that S-cones promote exploratory behaviour, opposing a suppressive effect on activity driven by L-cones. We further use c-Fos mapping and multielectrode recordings to demonstrate that these effects reflect differential neuronal activation of the hypothalamic subparaventricular zone, a key hypothalamic relay for behavioural control. We subsequently use in vivo multielectrode recordings to survey the sensory properties of the lateral hypothalamus (LH). Chapter 3 uses carefully calibrated polychromatic light stimuli to define the photoreceptor pathways influencing LH activity, identifying subsets of cells that do or do not receive input from intrinsically photosensitive retinal ganglion cells (ipRGCs) and populations of cells exhibiting colour-opponent or non-opponent cone inputs. Chapter 4 then uses more conventional visual stimuli to define the spatiotemporal tuning properties of LH cells, revealing a diverse array or sensory properties including cells tuned to detect local variations in radiance, spatial contrast and/or motion. Given the diverse roles of the LH (spanning regulation of feeding, sleep and defensive behaviours) collectively these data provide a substrate for far more a complex and sophisticated behavioural control via NIF system than previously envisaged.