GB950475A - Improvements in electric discharge lamps - Google Patents

Abstract

950,475. Discharge lamps. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 17, 1959 [Nov. 19, 1958], No. 37283/58. Heading H1D. A high or low pressure discharge lamp Fig. 1, comprises a sealed envelope 1 consisting mainly of metal having apertures 7 filled with a light transmissive vitreous material 6 continuous with a lining 8 of insulative vitreous material extending over substantially wholly the interior metal surface of the envelope. The vitreous lining 8 can be fluorescent or a phosphor coating 12a can be provided. The filling can be argon with a trace of mercury vapour. One or both of the electrodes 2 is mounted on a tube 4 used for evacuation and filling of the envelope. The seals at the ends of the envelope consist of metal stems 9 sealed at their outer ends to the wall of the envelope at 10, e.g. by welding or by a glass seal. Stems 9 are formed with a flanged inner end 11 apertured to receive the tube 4. The vitreous material used for filling the apertures 7 and forming the lining 8 should be compatible with the metal of the envelope 1. The envelope 1 can be made of a Ni-Fe-Co alloy and the vitreous material of a boro-silicate glass, or the envelope can be of iron or steel and the vitreous material of the glass described in Specification 572,020. The envelope 1 can be pierced from tubing or fabricated from sheets, strips or rods joined by welding. The envelope 1 can be dipped into molten glass or vitreous enamelling can be used. The envelope can be in the form of a hollow metal box 16, Fig. 2, having apertures 18 and partitions 15 extending between opposite walls to define a sinuous discharge path. Auxiliary electrodes can be fitted through ports 19 used for coating the metal envelope. The metal envelope can be coated on its inner surface with rhodium for light reflection or a coating of white vitreous reflecting enamel can be applied thereto. Alternatively a coating of reflecting magnesium or titanium oxide can be applied to the vitreous material. In the construction shown in Fig. 4 the envelope is in the form of a flanged metal tray 20 to which an apertured metallic cover member 21 is secured, the apertures 22 being sealed with glass or white enamel as described above. A central barrier member 26 is formed integrally with the tray to produce a circuitous discharge path and terminates in a wall 27 to which is attached a metal evacuating tubulation 29. In the construction shown in Fig. 6 the rims of the tray 20 and cover member 21 are welded together by a folded metal strip 34 and the tray is made of iron sheet covered with white enamel. The cover member 21 is curved and ribbed and the apertures therein are sealed by glass panes 38. Indentations 35 are formed in the base of the tray 20. The barrier member 26 is separated from the cover member 21 by a glass wool gasket 36. Modified constructions are described. The envelope can be formed of sheets of magnetic material, the discharge current then flowing within a magnetic circuit with an insulating gap between opposing faces of the magnetic sheets formed by the vitreous material. The reactive impedance thereby introduced into the circuit of the lamp is operated with A.C. at H.F., serves as part or all of the series inductance required to balance the negative volt-ampere characteristic of the discharge. Specification 603,326 also is referred to.