Abstract: The apparatus comprises at least one light source (3) and a plurality of test channels with in each case one optoelectronic converter (4a, 4b). In the light path between the light source and the converter is provided at least one light channel (5a, 5b) and the test material (1). The light channels are constructed as optical elements for bounding or defining a light bundle. A plurality of light channels is juxtaposed in a common casing (6a, 6b) on at least part of the light path. In each light channel can be provided a beam splitter element (12) and together form a single beam splitter (12) removably arranged in the casing. The converters (4a) can be juxtaposed on the same casing as the beam splitter (12) and each is associated with a light channel (5a). Two casings (6a, 6b) can be provided, the light source (3) in the first casing (6a) and the converters (4b) in the second casing (6b) are juxtaposed and associated with in each case one light channel (5a, 5b).