A controller for a lighting system, the lighting system comprising one or more luminaires associated with a lighting channel; the controller comprising: a script interpreter configured to interpret a lighting script for rendering on the luminaires; an effect impact determining module configured to determine a visual impact level of each of the lighting effects if rendered as defined by the lighting script unmodified; a script modifier configured to selectively generate, based on the visual impact levels, effect modification data for modifying the visual impact level of at least one of the lighting effects; a lighting controller configured to control the luminaires associated with the lighting channel to render versions of the lighting effects defined by the lighting script, wherein the lighting controller is configured to use the effect modification data to render a modified version of the at least one lighting effect having the modified visual impact level.