In mammals, melanopsin (OPN4)-based phototransduction is thought to account for most of the non-image-forming light detection that entrains the circadian pacemaker. van Oosterhout et al. now show that ultraviolet (UV) light-sensitive cones also make an important contribution to circadian regulation in mice. UV light had comparable phase-shifting effects to white light in a wheel running task. In wild-type and Opn4−/− mice, UV or white light exposure could elicit a sustained increase in neural activity in the suprachiasmatic nucleus, and UV light, like white light, was capable of inducing sleep. Lastly, loss of cones but not rods had a severe effect on UV light-induced phase-shifting responses.