Abstract: Stray light produced in a monochromator by the diffuse reflection of the incoming light beam specularly reflected from the surface of the diffraction grating is practically eliminated by interposing a black glass "absorbent-reflector" in the path of the specularly reflected beam. The small percentage of radiation that is not absorbed by the absorbing glass is reflected to an opposite blackened wall which diffuse reflects an extremely small percentage of the beam back to the absorbent-reflector where a very negligible part is returned to the grating surface and eventually to the monochromator exit slit.