Patent GB-752454-A (GB)
Title: Improvements in or relating to high-pressure electrical discharge lamps
IPC: H01J61/54
Filed: 1953-05-14
Abstract: 752,454. Discharge lamps. KREFFT, H. E. May 14, 1953 [Jan. 2, 1953], No. 13557/53. Class 39 (1). [Also in Group XXXV] A high-pressure, e.g. 5-50, preferably 20, atmospheres, discharge lamp 1 comprises a plurality of main electrodes 12, 13, at least one auxiliary electrode 14, 15, and at least one metallic conductor of heat-resistant material 16, Fig. 1, or 27, 28, Fig. 2, wherein the auxiliary electrode or electrodes are positioned adjacent one or a corresponding number of main electrodes, the metallic conductor 16 or conductors 27, 28 are connected to a pair 14, 15 or pairs 12, 14 and 13, 15 of electrodes, at least one electrode 14, 15 of the pair or pairs being an auxiliary electrode, and the metallic conductor 16 or conductors 27, 28 are so dimensioned that the passage of a current comparable to the operating current of the lamp heats the conductor or conductors to incandescence and produces therein a voltage drop of about the same magnitude as the operating voltage of the lamp. The lamp envelope can contain mercury, krypton or xenon, and cadmium and zinc, and the conductor 16 or conductors 27, 28 comprise a coil. or coils of tungsten wire, the diameter and length of which are such that they can be heated to incandescence at a temperature below 2000 K under a voltage of the same magnitude as the operating voltage of the lamp to form a H.P. mercury vapour atmosphere prior to starting a discharge, and can be heated to a temperature of 3000 K or more by a momentarily high starting current to produce initial arc discharges across the coils and auxiliary arcs between adjacent main and auxiliary electrodes or between pairs of auxiliary electrodes. The lamp may be provided with an outer envelope. The main electrodes 12 and 13 are of the selfheating type and consist of sintered bodies or closely wound wire coils of tungsten and the auxiliary electrodes are preferably of the preheated type and consist of coiled-coils of tungsten or can consist of closely wound coiled-coils slipped over the supporting wires 11. A construction of the heating and starting coil and of the auxiliary electrode for the arrangement shown in Fig. 2 is shown in Figs. 3 and 4 and comprises an auxiliary electrode 43 consisting of three secondary turns of a coiled-coil, one end 44 of which is slipped over the free end of the lead 41 and welded to it and the other end 48 of which is connected to the heating and starting coil 45 composed of four parallel co-planar coils the other end 46 of which is connected to the lead 40 to the main electrode 42 by a wire 47. Preferably the coiled-coil auxiliary electrode 43 is made from the same primary coil of which the coil 45 is composed. The auxiliary electrodes can be provided with activating materials. Loading of the envelope surface of less than 15 watts per sq. cm. is referred to. The circuit arrangement shown in Fig. 1 comprises chokes 17 and 18 and a switch 19 through which the main electrodes 12 and 13 are connected to an A.C. source 20 and switches 21 and 22 and resistances 23 and 24 through which the auxiliary electrodes 14, 15 and the coil 16 are connected through parts of the chokes 17, 18 to the source 20. Another circuit arrangement is shown in Fig. 2. The switches 21, 22, Fig. 1, and 30, 32, Fig. 2, are preferably magnetic which are interrupted when resistances 23, 24 and 29, 31, respectively, are short-circuited and the currents in the auxiliary circuits raised to high values, while re-setting of these switches is effected by hand when the main operating switch 19 is closed, or automatically by a voltage-responsive element controlled by the lamp voltage. The resistances 23, 24 and 29, 31 preferably consist of temperature-dependent semi-conductors having cold resistances which correspond to the desired additional resistances in the auxiliary circuits, and time characteristics for breaking down in accordance with the required heating period of the lamp.