GB803536A - Improvements in incandescent electric lamps - Google Patents

Abstract

803,536. Electric incandescent lamps. GENERAL ELECTRIC CO. July 4, 1956 [July 13, 1955], No. 20724/56. Class 39(2) An electric incandescent lamp comprising a sealed envelope 1 having a concave light-concentrating reflector portion 1, an opposed transparent window portion 3, and a concentrated filament 5 located substantially at the focus of the reflector is characterized in that the reflector is highly reflective of visible light rays and also highly transmissive of infra-red rays, and a shield 13 is arranged adjacent to the filament and between the filament and the window 3, the shield being shaped and proportioned to intercept the radiation emitted directly from the filament toward the window. In the example the lamp 1 is of the sealed beam type comprising a glass reflector portion 2 and a lens or window portion 3 hermetically fused together, the reflector portion having previously been coated with a film 11 of semi-conductive material such as germanium, silicon, antimony-sulphide or selenium, covered by a single film 12 of dielectric such as zinc sulphide of such thickness as to reduce the infra-red reflectance. The film 12 of dielectric should have an optical thickness equal to one-quarter the wavelength of near infra-red light, and an index of refraction equal to the square root of the index of refraction of the semiconductor 11 in the same wavelength region. In an example a laver 11 of germanium of a thickness which transmits approximately 20 per cent of visible radiation is coated with a layer of zinc sulphide having an optical thickness of approximately 250 millimicrons. The filament 5, which is of any desired concentrated configuration, and preferably located at the focus of the reflector portion, is located approximately at the centre of a shield 13 which may be of spherical section. The shield is preferably constructed of highly reflective material such as iron, nickel, or molybdenum or a non-metal such as sintered alumina or magnesia. U.S.A. Specification 2.660.925 is referred to.