A versatile apparatus is described for use in studying electroluminescence and electrophotoluminescence. Measurements of light emission can be made with electrical excitation frequencies ranging from dc to 400 Mc and also in selected microwave bands. Oscillators that may be employed over this frequency range are discussed. The apparatus consists of a crystal mount and a simple optical system for irradiation and for the separation of excitation and luminescent spectra. Flat plate‐type as well as long silver‐type crystals are mounted on slides which can be easily interchanged. Tests may be run from low temperatures (−70°C or lower) up to about 300°C.