GB995419A - An electric discharge lamp - Google Patents

Abstract

995,419. Discharge lamps; electrode materials. PATENT-TREUHAND-GESELLSCHAFT FUR ELEKTRISCHE GLUHLAMPEN. July 26, 1961 [July 27, 1960], No. 27094/61. Heading H1D. An electric discharge lamp filled with metal vapour and/or rare gas and operating at a loading of more than 10<SP>4</SP>W/cm.<SP>3</SP> and at a pressure of more than one atmosphere comprises a cathode 2 and anode 3 connected to a D.C. supply to set up a basic discharge and a third electrode 4 arranged laterally of the line between the electrodes 2 and 3 and nearer to the cathode 2 and connected as an additional cathode in a circuit supplying a continuous or pulsating D.C., the electrode 4 being so dimensioned and positioned in relation to the basic discharge and the current which it carries during operation being so chosen that a discharge without cathode spot originates on it. The envelope can be of quartz glass, glass, aluminium oxide or of metal with windows. The metal envelope can form one of the electrodes, e.g. the anode. The basic discharge can be operated with relatively low power consumption and the current supplied to the third electrode can have a much higher value than that of the basic discharge. The third electrode can be in the form of a ring 7, Fig. 2, surrounding the arc of the basic discharge and in a plane at right angles to the direction of the basic discharge. The anode can be an annular electrode and can have an insulating layer on the side facing the cathode. A material which reduces the work function of the electrons and facilitates the formation of a discharge without cathode spot can be added to the material of the third electrode. The third electrode can consist of tungsten with an addition of thorium oxide or lanthanum boride, or can consist wholly or partly of thoriated tungsten, tantalum or hafnium. The third electrode can be provided with a groove facing the basic discharge which groove is filled with an activating material. The filling of the lamp can contain a material, e.g. a halogen or a halogen compound, which forms with the material of the third electrode, e.g. tungsten, a compound having a higher vapour pressure than the electrode material at the temperature prevailing in the lamp and dissociating at the high temperatures in the arc starting at the third electrode-this purifies the envelope. Magnetic displacement of the discharge can be prevented by effecting the current supply to the ring-shaped electrode 7, Fig. 2, at two oppositely arranged supply points or at several supply points arranged symmetrically, or by arranging that the conductor for the current supply to the third electrode forms outside the envelope one or several turns which lie substantially in the plane defined by the axis of the basic discharge and the direction of the current inlead to the third electrode within the envelope. The filling can be xenon or krypton at an operating pressure of 1-50 atmospheres.