[en] Highlights: • The mechanism explaining the emission pattern of perylene α-crystals was revealed. • Light propagating in the crystal was coupled to microspheres on the crystal surface. • The pattern is due to the waveguide effect and total internal reflection at the edges. Square single crystals of perylene (α-crystals) exhibit a peculiar emission pattern when excited by a focused laser beam. Fluorescence spots are observed at the point of excitation and at four edges, with the lines connecting the excitation point and edge emissions being perpendicular to the edges irrespective of the excitation position. Two different mechanisms explaining this emission pattern have been proposed so far. Our newly designed experiment and analysis revealed that the involved mechanism features a combination of the waveguide effect and total internal reflection by crystal edges.