Proposed is an illumination system (100) comprising a plurality of light sources (10) provided with encoders (20) arranged to enable light emitted from the light sources to comprise light source identification codes. In order to enable light effect commissioning, i.e. correlating the light sources (10) with their illumination footprints (11), the system further comprises a camera (40) arranged to register images of illumination spots (11), and a signal processor (111) arranged to derive the light source identification codes from registered images. Arranging the encoders (20) to modulate the light emitted at a frequency above a predefined high level to comprise fast codes (12) and at a frequency below a predefined low level to comprise slow codes (13), beneficially allows for the use of simple low cost camera systems.