GB1164293A - Improvements in or relating to Electric Discharge Lamps. - Google Patents

Abstract

1,164,293. Metal-vapour lamps. GENERAL ELECTRIC & ENGLISH ELECTRIC COMPANIES Ltd. 7 July, 1967 [14 July, 1966; 23 Feb., 1967], Nos. 31723/66 and 8630/67. Heading H1D. In a lamp as described in Specification 1,065,023 having an envelope 1 of material having an alumina content exceeding 85% by weight to which a niobium closure member 3 supporting an electrode 7 is sealed by a layer 5 consisting of at least one of the metals Ti, Zr, Va, Hf optionally together with Nb, as described in Specification 1,094,052, a shield 16 of refractory material is provided to protect the seal 5 from wandering of the discharge during starting of the lamp. The shield may be an annular disc of ceramic material similar to that of the envelope 1 fitted around the electrode 7 near the seal 5, or may be of metal, e.g. W or Mo, fitted near the discharge end of the electrode. Alternatively the shield may be a frusto -conical member of sheet metal or of coiled wire, in which case it may form an extension of either the innner coil 8 or (as shown) of the outer coil 15 of two tungsten coils retaining electron emissive material 9 on the electrode 7. A cylindrical extension 17 of the shield lies near the envelope 1. In a modification (Fig. 2, not shown), a frusto-conical coiled wire shield mounted with the narrow end towards the seal has at the wide end a cylindrical extension in contact with the lamp envelope and at the narrow end a cylindrical extension fitting closely around the electrode and in contact with the exhaust tube 12 or with the closure member. The lamp which has a filling of sodium, mercury and argon is mounted in an outer glass envelope.