The present invention relates to a control system (13) and method for controlling the light output of an emitting unit (11) having at least one LED (15) and emitting light of at least one color. The control system (13) comprises a feedback based on a detection unit (19) detecting the light output of the emitting unit (11), a detection pulse generator (27), a suppression unit (23) suppressing environmental light interferences in detected light, and a control unit (21) for controlling the light output of the emitting unit on basis of a comparison between a reference signal representing a desired light output of the emitting unit and an output signal of the suppression unit. The detection pulse generator (27) generates detection pulses a-periodically. Thus, an a-periodicity is introduced into the feedback processing of the light output. This provides a possibility by means of conventional suppression algorithms to eliminate or reduce interfering environmental light, particularly pulsed light.