Microalgae have recently attracted attention for their potential to produce high added compounds, proteins, and even biofuels. Our paper seeks to develop a control strategy for light-limited continuous culture imposing a stress for which microalgae have to adapt. This operating mode - called photoinhibistat - consists, for a culture with a constant dilution rate, in varying the incident light in order to regulate the light at the bottom of the reactor, inducing a light stress. Based on a simple model of light-limited growth, we analyze the dynamics of the photoinhibistat in monoculture and in competition. It appears that the photoinhibistat can be used to select, from the initial microalgae population, the strain with the highest resistance to photoinhibition.