GB1193095A - Improvements in or relating to Self-Starting Arc Lamps. - Google Patents

Abstract

1,193,095. Discharge lamps. PEK LABS Inc. 24 Oct., 1967 [24 Feb., 1967], No. 48197/67. Heading H1D. A self-starting short arc lamp of the type described in Specifications 1,080,606 and 1,042,213, comprising electrodes 16 and 18 connected by a bridgewire 50 which fuses to start the arc on the application of the normal low voltage main power supply, is characterized in that the bridgewire has a looped configuration so that its ends are pressed into resilient contact against the electrodes near the electrode arc ends. In Fig. 3, the electrodes are provided with slots 60 and 62 in which the wire 50 is a sliding fit, the ends of the wire being welded to the electrodes by means of platinum tabs 52 and 54. The distance A between the exit end of each slot and the apex of the electrode should be between one and four times the diameter of the wire, the optimum distance being two diameters. The free length of the wire should be between one and a half and five times the gap length G, the arc length of the loops correspondingly lying between 90 and 270 degrees and being 180 degrees in Fig. 3. In a modification (Fig. 5, not shown), the wire is formed into a single loop describing an arc of between 90 and 270 degrees. With this arrangement, when the electrodes are not identical the cathode slot may be closed by swaging so that the bridgewire is captured and cannot escape (Fig. 7, not shown). The looped structure of the bridgewire enables it to withstand shock such as is experienced in a missile. The electrodes may be disposed in a quartz envelope which is shrunk round the electrodes and filled with inert gas such as xenon at a pressure of 10-15 atmospheres at room temperature rising to 15-30 atmospheres at operating temperature.