Abstract: This luminaire comprises a reflector of transparent material having a prismatic outer surface that includes many juxtaposed prisms. Each prism includes two reflecting surfaces meeting at an apex and having portions disposed to effect total internal reflection of a large percentage of the light rays from the light source of the luminaire. Immediately adjacent the outer surface of the reflector, there is a cover of substantially transparent material that protects the prism reflecting surfaces from deposits that could interfere with their total internal reflecting properties. The cover is spaced from the prismatic outer surface at substantially all points on the prism reflecting surfaces where such reflecting surfaces are disposed to effect total internal reflection of the light source rays.