Abstract: An optical radiation detector utilizes a unitary V-shaped or conical reflector element located within an internal cavity of an optically transmissive capped housing to provide a 180.degree. cylindrical swath or 2.pi. steradian hemispherical field-of-view in a compact package. Radiation from a central portion of the field-of-view received into the open top of the reflector is directed by internal reflective surfaces through an apex aperture onto a central sensing element. Radiation from peripheral points of the field-of-view received outside the open top is directed by external reflective surfaces outside the apex aperture onto outer sensing elements. Bandwidth filtering of the sensed radiation is provided either by selection of material for the cap, or by adding an optical filter plate between the reflector and sensing elements. The reflector is attached either to the undersurface of the cap top, or above the filter plate.