A light source unit may include a cooling device a luminescent substance an excitation radiation source having a laser source and an optical element arranged between the radiation source and the substance wherein the cooling device constitutes a heat sink, wherein the substance is linked thermally to the heat sink and wherein the optical element is designed as an integrating optical element and is coupled between the radiation source and the substance in such a mariner that a part of the radiation emitted by the radiation source, entering in an acceptance angle range of the integrating optical element, is subjected to an internal reflection in the optical element before it exits the optical element and strikes the substance, and that a part of the radiation emitted by the substance enters the optical element and exits the optical element as effective radiation.
