The present invention relates particularly to photovoltaic systems for use in photovoltaically generating electrical energy. This is achieved according to the invention in that beneath the nozzle head in the annular body a channel is provided, which is connected to a compressed air line, which in turn is linked to the compressed air feed line, wherein the channel in the upper edge pointing to the nozzle head forms an annular gap \u2014triggering the Venturi effect. The apparatus has a support plate for fixing the optical fibers to the back surface of the liquid crystal display panel, and an optical diffusing unit for optically connecting the light source to the optical fibers. The multilayered stack of the casing may further include a spacer arrangement, either as a separate layer between the base layer and the scattering layer, or as an integrated arrangement of one or both of the base layer and the scattering layer.