GB573141A - Improvements relating to electric discharge lamps - Google Patents

Abstract

573,141. Discharge lamps. SIEMENS ELECTRIC LAMPS & SUPPLIES, Ltd., ALDINGTON, J. N., and MEADOWCROFT, A. J. Nov. 12, 1940, No. 16371. [Class 39 (i)] [Also in Group XI] Starting of a discharge lamp of the highpressure mercury vapour compact source type is effected by an auxiliary-filamentary electrode 11 heated independently from a transformer 18, 19, Fig. 5, placed on the lamp side of the ballast 17. The filling has also argon or neon or a mixture thereof at a pressure up to 100 mm. or more. Foliated seals 5, 6, as described in Specification 541,208, [Group XXXVI], lead to the main electrodes 3, 4, the shanks 9 of which are divided by a butt joint to limit heat transfer from the heads 8 to the seals ; the electrodes are tungsten with a thorium or barium compound incorporated and are wound round with tungsten wire 10. The arc is below the lamp centre in a vertical lamp, the upper electrode being heavier than the lower particularly on a D.C. circuit. To maintain the vapour pressure a heater coil may surround part of the bulb and also the upper part of the seal or the latter only, and maintain a local temperature of 750‹ C. To start the lamp the heater circuit is closed by the switch 16 and thereafter is opened to allow full pressure drop across the auxiliary primary 18 which causes rapid ionization of the filling by a discharge between the electrodes 4, 11 ; re-ignition is readily effected when the lamp goes out without the necessity of complete cooling. On a D.C. supply a rotary converter may provide the ionizing discharge, the auxiliary heater being supplied from the D.C. or from an A.C. source. An inductance may be included in series with the lamp which may cause a surge on opening the switch 16 ; the heater coil on the lamp may be used for this purpose. The heater may run permanently. Dimensions of one construction are given with loading. Cooling at the seals may be provided. For use as a projector the lamp is supported by springs 29, Fig. 6, from rods 23 fixed in annuli 21, 22, the springs engaging brackets 27 around the seals ; terminal clamps 31 are provided for the main electrodes and the auxiliary electrode leads are carried to binding screws 26 on the annulus 22. The brackets act as cooling fins for the seals and a jet of water or air may be blown on the lamp. The lamp is mounted with the annulus 21 facing the reflector.