The Arctic is characterized by an extreme light climate. Life history events such as reproduction and seasonal migration need to be timed to account for pulsed periods of primary production, and diel activities need to be upheld in periods of continuous light or darkness. Under climate warming, the light regime in the water changes as sea ice extent, thickness, and duration are decreasing. At the same time, zooplankton species experience biogeographical northward shifts following the increased inflow of warmer Atlantic water in the Arctic. This exposes them to stronger seasonal fluctuations in light intensity and photoperiod. The consequences of changes in light climate on Calanus spp. are completely unknown but may trigger behavioural and physiological responses that will alter productivity and disrupt energy flow in Arctic food webs, with implications for northern communities depending on the services provided by the Arctic marine ecosystems.