GB1330214A - Vapour discharge lamps - Google Patents

Abstract

1330214 Lamps THORN ELECTRICAL INDUSTRIES Ltd 16 June 1972 [7 Sept 1971] 41727/71 Heading F4R [Also in Division H1] A vapour discharge lighting unit includes a light-transmitting arc chamber 11 provided with electron-emitter electrodes 20 and containing a metal or metal compound the vapour of which in use supports an arc discharge emitting resonant radiation between the electrodes, and a bowl reflector 12 associated with one or both electrodes and so located outside the chamber as to collect a proportion 24, 25 of the said resonance radiation from the discharge region and reflect the collected radiation towards a space within the chamber outside the discharge column and behind the associated electrode. In the embodiment shown the bowls 12 are part ellipsoidal and are secured to nibium caps 16 and 17 closing the ends of the sintered alumina tube 11 and supporting electrodes in the form of tungsten wires 20 carrying tungsten coils 21 coated or impregnated with electron, emissive material. A filling, e.g. of sodiumxenon and mercury is introduced through a niobium exhaust tube 18. Fillings of other alkali metals may be employed, or halides if the arc tube 11 is made of fused silica. The reflectors 12 instead of being of metal may be of the interference or dichroio type to transmit visible light while reflecting infra-red radiation or to trasmit U.V. while reflecting light of longer wavelengths. The arc tube 11 may be U-shaped so that only one reflector 12 is necessary. A single reflector also suffices if the lamp is operated on D.C. As an alternative to enclosing the arc tube 11 and reflector(s) 12 in an outer evacuated envelope 13, the reflector(s) may be built into a light fitting in which the arc tube 11 is supported.