an improved signal light employing a deep - dish reflector and critically positioned mask or masks for blocking at least some selected light rays having their origin in an external source to reduce , or eliminate , phantom signals . the mask is effective to block out at least a portion of the reflector which reflects light , from an external source , back out of the signal in a direction parallel to the reflector axis . the mask may take the form of a planar ring , a cylindrical surface , a cone or portions thereof . other shapes may prove expedient or the reflector may be treated in selected and controlled locations to inhibit reflection . the mask may comprise any suitable material such as an opaque material or an electrically controlled optical shutter which is closed when it is desired to inhibit phantom signals and opened to accommodate normal signals .