GB441888A - Improvements in electric lighting devices - Google Patents

Abstract

441,888. Discharge lamps. GREETHAM, E., 29, Hillside Court, Finchley Road, London. Aug. 9, 1934, No. 22995. [Class 39 (i)] [See also Group XI] An electric, gaseous or vapour arc discharge lamp has two envelopes transparent to ultra-violet radiations and a surrounding transparent or translucent element containing or coated with fluorescent material. In the form shown in Fig. 1, the lamp comprises a discharge device 1, the double walls 4, 5 of which are made of quartz, a hood 2, and a fluorescent screen 3. The space between the walls 4, 5 may be evacuated or sealed to prevent the circulation of air. If the screen 3 is coated on its inner surface with the fluorescent material it is not transparent to ultra-violet radiations, particularly those of short-wave length, but if it contains the fluorescent material it is transparent to ultra-violet radiations and is preferably surrounded by a further screen which is not transparent to ultra-violet radiations, particularly those of short wave-length. The screen 3 may comprise a two-ply structure, the inner ply being transparent to ultra-violet radiations and containing the fluorescent material and the outer ply of opal or translucent glass. Alternatively, the outer wall 5 may contain or be coated with the fluorescent material, and the screen 3 made of plain or opal, ribbed or prismatic glass, preferably not transparent to short-wave ultra-violet radiations. In the form shown in Fig. 2, the diffusing element 3 is made prismatic and the discharge device 1 is surrounded by a separate fluorescent screen 6 which seats against a packing ring 7 on the hood 2 so as to prevent the circulation of air. Alternatively, the screen 6 may be sealed to the discharge device 1 and the space therebetween evacuated.