Our daily cycle of work, rest and sleep results from interactions between external stimuli (e.g. night/day) and an internal circadian clock, first discovered in Drosophila. Our problem is that the way that light keeps this internal clock synchronised is still mysterious. We will address this by building a contactless device to measure circadian visual rhythms using the latest optogenetic tools. We will optimise conditions to allow assessment of visual sensitivity without impacting the daily rhythm. This will be scaled up for simultaneous work with 16 flies to genetically dissect the interaction between light and the circadian clock.