GB660258A - Improvements in and relating to electrode structures for high pressure electric discharge devices - Google Patents

Abstract

660,258. Electric discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 29, 1948 [Jan. 29, 1947], No. 2704/48. Addition to 645,122. Class 39 (i). The main electrodes 3 of a high-pressure discharge device, e.g. a mercuryvapour lamp, are of refractory metal, such as tantalum, and comprise a disc portion 21 provided on one surface with one or more ridges 22, for the purpose of increasing the electron - emitting surface without substantially increasing the depth of the electrode. As shown, the ridges are formed by a spiral of the refractory metal, but in modifications, Figs. 4-9 (not shown), they may comprise one or a number of concentric cylinders, formed either by ribbons or by one or more nested cup-shaped members secured on the disc 21. The latter is secured to the lead-in wire 10 by a wire 26 welded to a metal disc 23 which is separated from disc 21 by a metal ring 24 and a refractory wire 25. Details of the sizes of the ridges are given. The lamp envelope contains a starting electrode and a starting gas, e.g. argon, krypton or xenon at a pressure of e.g. 17 mm. of mercury. The envelope also contains an ionizable working substance, e.g. mercury, the lamp being arranged to operate in the pressure range of from“ to 2 atmospheres. The ridges are also stated to aid thermal conduction in the electrodes and so avoid "hot-spotting" and possible disintegration thereof.