GB1024182A - Improvements in or relating to high pressure electric discharge lamps - Google Patents

Abstract

1,024,182. Discharge lamps. GENERAL ELECTRIC CO. Ltd. Jan. 2, 1964 [Jan. 30, 1963], No. 3819/63. Heading H1D. In a high pressure discharge lamp containing mercury, a rare gas and an alkali metal halide, e.g. sodium iodide, at a total operating pressure of at least 500 mm. of Hg, each of the two main electrodes is unactivated and consists only of a coil of tungsten wire wound around a tungsten rod, there being at least one empty space between the coil and the rod so that increased heating of the adjacent part of the coil during starting is sufficient to maintain an arc. The empty space may be provided by forming a recess in the tungsten rod, or by using a double coil witha gap in the inner winding and possibly also a two-part tungsten rod 18, 19 as shown, which also prevents over-heating of the electrode-to-envelope seal 6, 7. During lamp operation, at least partial dissociation of the metal halide vapour occurs; and the envelope temperature near the electrodes is maintained sufficiently high, i.e. at least 800‹ C., to avoid rapid formation of a sputtered tungsten film, by sealing the electrodes into frustoconical end portions of the envelope, or by thermally insulating the ends of the envelope with an external coating of heat-conducting paint, e.g. platinum. The lamp may comprise auxiliary electrodes, Fig. 1 (not shown). Specific dimensions, electrical data, and gas fillings are given.