Abstract: In order to improve the sensitivity and the spectral resolution in measuring the luminescence of diverse sample materials, adapted optical imaging relationships at variable excitation output are provided for the different optical paths of the luminescence light emitted by the sample material. An excitation bundle of rays which can be stopped down and the central beam of the secondary beam which emanates from the sample material, are directed to be parallel to one another. A mount is displaceable along the parallel bundles of rays, the sample material and a collecting optical member being fastened on the mount at a distance from one another equal to the focal length of this optical member.