Abstract A new method for investigation of reflection in thin, plane-parallel layers is presented. An experimental analysis on the luminescent dye rhodamine 6G confirms the results of the theoretical model. The results reveal that reflections can increase the number of excited luminescent centers considerably, to an extent depending on the concentration of the luminescent dye, and the thickness and size of the layer. As regards the influence of reflection, the optimal dye concentration can be determined both theoretically and experimentally. The results can be utilized for the optimization of luminescent solar concentrators.