The invention concerns a light source unit of tunable spectral properties, having a pump light source and a phosphor element for a conversion of pump light into converted light intended for illuminating a target, wherein the phosphor element has at least two phosphor element sections interacting differently with pump light, and wherein the light source unit further comprises a deflecting unit, such as a zoom lens or a variable diffraction grating, for deflecting the pump light so as to vary a distribution of pump light incident onto the phosphor element with respect to the different phosphor element sections, in order to vary spectral properties of the combined converted light beam emanating from the light source unit.
