Light governs primary production, phytoplankton bloom phenology, and carbon export in the Southern Ocean, yet our predictive capabilities in this area are limited. This is partly because the causal linkage between fluctuating light regimes and phytoplankton physiology is not yet understood due to uncertainty in which aspects of the light environment drive changes in phytoplankton growth and photophysiology. In this study, we expose Southern Ocean phytoplankton across a multivariable matrix of different parameters of the light regime (e.g., maximum, median, dose) and measure changes in phytoplankton physiology. Our results unravel how acclimation strategies differ according to light regime parameters and improves our understanding of how light history affects phytoplankton physiology. These results will better inform our understanding of photoadaptation under fluctuating light regimes and help to refine photosynthesis and primary production models. In doing so, this study betters our understanding of how phytoplankton will respond to changes in ocean stratification and vertical mixing predicted for the future Southern Ocean.