GB474779A - Improvements in and relating to lamps for projecting light beams - Google Patents

Abstract

474,779. Searchlight, signalling, &c. light projectors. BRITISH THOMSONHOUSTON CO., Ltd., and FAIRBROTHER, J. A. V. May 7, 1936, No. 12940. [Classes 75 (ii) and 75 (iv)] A searchlight, signalling, or like light projector comprises a super high pressure electric discharge lamp mounted at the focus of a reflector, all or part of which is enclosed by a transparent member, and the enclosed portion filled with a circulating cooling fluid which is introduced through the apex portion of the reflector. The reflector may be made of metal such as polished stainless steel or a base metal coated with silver or cadmium, of glass with a reflecting coating on its front or rear surface, or of a synthetic resin with a polished or metal coated inner surface. The cooling fluid may be water, mixed or not with glycerine or like substance of high refractive index, or it may be a liquid which absorbs ultra-violet rays. Fig. 1 shows a super high pressure mercury vapour lamp 9 at the focus of a paraboloidal reflector 1 which is closed at the front by a flat glass plate 3, cooling fluid entering axially at 14 and escaping through a top outflow pipe 15. Direct rays are intercepted by a spherical recuperating reflector 30. The plate 3 may be replaced by a planoconcave or convex lens. When a part only of the reflector is enclosed by the transparent member, the latter is disposed at right-angles to the axis of the reflector and at a sufficient distance to prevent internal reflection at the inner surface of the transparent member. Fig. 5 shows an ellipsoidal reflector 34 having foci F<1>, F<2>, a spherical recuperating reflector 31, and a spherical closure plate 32 having its centre at the focus F<2>. The rays may be brought to a focus F<3> by means of a planoconcave condensing lens 33, or into a parallel beam by means of a lens such as 33 having its focus at F<2>. Transparent parts of the lamp, instead of being made of glass, may be made of the material known as Glyptal. U.S.A. Specification 1,973,132 is referred to.