System to test performance of pixels in a sensor array

A system to test operation of an optical sensor (50) is disclosed. The optical sensor (50) includes one or more photosensitive devices (80) configured to convert light to electrical signals. A test light source (60) and a reference target (76) are included within the housing (52) of the optical sensor (50). The test light source (60) is mounted proximate to the photosensitive devices (80) and the reference target (76) is positioned opposite from the test light source (60). The test light source (60) is periodically pulsed on to emit light (62) at a known wavelength. The light (62) is reflected from the reference target (60) back to at least a portion (82) of the photosensitive devices (80). A logic circuit uses the reflected light (64) which is received at the portion (82) of the photosensitive devices (80) to determine the distance between the light source (60) and the reference target (76). This calculated distance is compared against the known distance to verify correct operation of the optical sensor (50).