A compound light source is characterized by an output spectral measure that lies within a spectral measure design range and an average light intensity per component light source that lies within an output intensity design range. The plurality of component light sources includes light sources whose spectral measure value and output intensity lie outside the corresponding design ranges. The component light sources are chosen from a number of predetermined groups obtained by sorting the component light sources with respect to the spectral measure value and output intensity of each source such that the compound light source has a spectral measure value and output intensity that lies within the corresponding design ranges.