Abstract: Incandescent lamps or arc lamps having an infrared red reflecting multilayer optical interference filter on the outer surface of the vitreous or fused quartz lamp envelope enclosing the filament have a light-scattering coating applied over the filter to scatter light emitted by the lamp and thereby diffuse the filament image. The light-scattering coating consists of light-scattering particles, such as alumina, dispersed in a silica matrix. This coating is formed by applying to the filter a silicone solution in which is dispersed colloidal silica and light-scattering particles and pyrolyzing at high temperature to drive off the organic components and form the silica matrix.