GB755155A - Improvements relating to light projection devices - Google Patents

Abstract

755,155. Lamp projector lenses; electric incandescent lamps. BRITISH THOMSONHOUSTON CO., Ltd. June 21, 1954 [June 29, 1953], No. 18165/54. Classes 39(2) and 75(2). A lens for a light projector for airport approach illumination and having a concave paraboloid reflector 3, Fig. 1, and a planar light source 6 extending parallel to the reflector axis and consisting in three side-by-side coiled segments 6<SP>1</SP> and two end segments 7 with the centre segment centered at the focus of the reflector 3, so as to redirect beams from the reflector into a smooth rectangular patterned light beam of uniform sectional light intensity with a sharp cut-off at the boundaries of the rectangle, comprises in a central area on its inner face horizontal primary, preferably concave, flutes 16-23, Fig. 2, for vertically spreading the light rays passing therethrough and at the .portions of the lens other than at lateral side portions D thereof, a series of secondary vertically extending, preferably concave, flutes 24 in areas A, A<SP>1</SP>, 25, in areas B, B<SP>1</SP>, 26, in area C superimposed on the flutes 16-23, the flutes 26 in a central zone C being of horizontal lesser light spread, e.g. 28 degrees than the others of the secondary flutes 24, 25 e.g. 40 degrees and 36 degrees respectively and in the side portions D, superimposed on the primary flutes, vertically extending left and right bending prisms 27 for refracting e.g. at 14 degrees the light rays one half to each side of the projected beam. These prisms 27 may also be vertically fluted to spread horizontally by e.g. 2 degrees the rays passing therethrough so as to smooth out the portions of the beam produced by the side portions of the lens. These prisms may also take the form of right-angled triangles so as to be completely left-bending or right-bending. The primary flutes in the central parts of areas B, B<SP>1</SP> may have a vertical light spread of 10 degrees and in the other areas, of 15 degrees. The lens is shown as incorporated in a lamp of the "sealed beam" type described in Specification 515,091 fusion sealed at its periphery 2, Fig. 1, to the rim of a preformed glass paraboloidal reflector section 3 to form the envelope of the lamp. The segments 6<SP>1</SP> of the filament 6 are supported at their bight portions by supplementary support wires 9 anchored in an insulation bridge 10 fastened across the lead-in conductors 8 secured to metal thimbles 11 fusion-sealed at their rims to the exterior of section 3 and covered by an insulation cap 13 fitted over prongs 12 of blade type secured to the thimbles, the cap 13 being held in place as by bent out tongues on the prongs. The lamp envelope is exhausted and may be filled with an inert gas such as argon, nitrogen or mixtures thereof.