In our experiments on the butterflyPapilio xuthus and the Japanese quail Coturnix coturnix Japonica, using radioluminous paints, we obtained results that may lead to a useful method for experiments directed toward detecting systems of photoperiodic reception in animals. Instead of the usual electronic source method, we applied inorganic phosphorescent paints LC-GIH (for both P. xuthus and C. coturnix ) and LC-RIA (for C. coturnix) on the area believed to be related to the photoreceptor mechanism(s) of each animal. These inorganic paints were excited continuously by beta irradiation from tritium contained in the paint's binder and emitted particular lights (green-yellow light from LC-GIH; orange-red light from LC-RIA) as self-luminous phosphorescence. These light beams apparently penetrated into the animal tissue in some way and activated the photoreception mechanism(s).