GB1522036A - High pressure electric discharge lamps - Google Patents

Abstract

1522036 Metal vapour lamps GENERAL ELECTRIC CO Ltd 11 Nov 1976 [12 Nov 1975] 46699/75 Heading H1D In a h.p. discharge lamp with Hg, rare gas and one or more volatile metal halides, working at a total pressure of at least one atmosphere, with a tubular discharge envelope, e.g. of fixed silica, running horizontally, to improve temperature distribution and arc stability a W wire electrode at each end supported by a sealed-in lead 3, e.g. a Mo foil pinch, comprises outer 5, central 6, and inner 7 section with the outer 5 attached to the lead 3, the central section 6 running inclined to the axis towards some part of the cylindrical wall, and the inner section 7 extending into the discharge envelope so that it lies between the said part of the cylindrical wall and the axis, and the discharge path between the free ends lies parallel to the axis. Any of the sections of each electrode may include or be formed of a coil of wire 8 or the three sections may each be straight with a coil supported on one of them; an emissive material may be contained in a coil or coiled part of the electrode, in which case an outer coil may surround it. The lamp mounting should ensure that the inner ends of the electrodes lie at the lowermost position in the envelope. The end pinch seals of the electrodes should preferably be above the axis to avoid liquid halide attack on the sealed leads; an auxiliary electrode may also be fitted in the same pinch. A suitable lamp contains Hg, Xe or Ar, NaI, ScI 3 , and may be mounted in a glass outer envelope, which may contain N 2 and may be coated with an IR reflective coating of, e.g. SnO 2 or In 2 O 3 .