Background light intensity (irradiance) substantially impacts the visual code in the early visual system at synaptic and single-neuron levels, but its influence on population activity is largely unexplored. We show that fast narrowband oscillations, an important feature of population activity, systematically increase in amplitude as a function of irradiance in both anesthetized and awake, freely moving mice and at the level of the retina and dorsal lateral geniculate nucleus (dLGN). Narrowband coherence increases with irradiance across large areas of the dLGN, but especially for neighboring units. The spectral sensitivity of these effects and their substantial reduction in melanopsin knockout animals indicate a contribution from inner retinal photoreceptors. At bright backgrounds, narrowband coherence allows pooling of single-unit responses to become a viable strategy for enhancing visual signals within its frequency range. •Narrowband oscillation amplitude in retina and dLGN is largely defined by irradiance•At high irradiances, control of oscillations originates with melanopsin photoreception•Daylight irradiance monotonically increases narrowband coherence•Narrowband coherence amplifies visual responses within its frequency range Storchi et al. find that daylight irradiance, through melanopsin, systematically modulates amplitude of narrowband oscillations in mouse retina and dLGN and boosts visual signaling.