A display system includes a light source 110 and a spatial light modulator 122 located to receive light from the light source. The spatial light modulator (e.g., a DMD) includes a number of independently controllable elements that are activated for a period of time to display light of a desired brightness. A light sensor 136 is located to determine a characteristic of light from the light source 110. A control circuit 126 is coupled to the spatial light modulator 122 and controls the period of time that the independently controllable elements are activated. This period of time is based at least in part by an input received from the light sensor 136.