Abstract: A back light illumination system for providing substantially uniform illumination to a surface of an object to be observed so that the object may be accurately perceived by a machine vision system. The back light illumination system includes a light transmissive element having a central light transmissive portion and an opaque perimeter portion. A diffuser is located to cover the entire light transmissive portion and a rear surface of the diffuser is provided with a transmissive right angle film. A pair of opposed light sources are provided for illuminating a rear surface of the transmissive right angle film to supply light to the diffuser which uniformly diffuses the light and provides lighting of a substantially equal intensity and character to the light transmissive portion of the light transmissive element so that the back light illumination system thereafter emits substantially uniform illumination.