Abstract: Apparatus for use as a lighthouse in the manufacture of a color cathode ray tube (CRT) includes a housing with a cover lens. Disposed within the housing is a light source assembly including a light source in the form of a cylindrical shaped mercury lamp and an optical aperture closely spaced to the mercury lamp. The mercury lamp directs light through the optical aperture as well as through the cover lens onto the inner surface of the CRT's glass faceplate in a photo-stenciling process for registering, or aligning, phosphor dots on the faceplate's inner surface with electron beam passing apertures in the CRT's color selection electrode, or shadow mask. The optical aperture is elongated, with its longitudinal axis aligned generally transverse to the longitudinal axis of the mercury lamp, and is curvilinear having from two (2) to eight (8) inflection points along its length.