Generating mixed light colours

Generating mixed light colours using individually pulse width modulated light sources 11, where the brightness of colours can be changed by varying the successive periodic duty ratios of the current flowing to the light source. A lower constant current intensity is made available to the light sources, while simultaneously lengthening the current flow time span (duty ratio) within the period P. The total current time integral that arises corresponds to the current time integral of the predetermined duty ratio for the period. The current dependent drift of the colour locus of the light source is compensated for by changing the driving of different coloured light sources.