GB1041461A - Improvements in or relating to metallic-vapour discharge lamps - Google Patents

Abstract

1,041,461. Metal-vapour lamps. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Jan. 28, 1964 [Feb. 19, 1963], No. 6688/63. Heading H1D. A metal vapour discharge lamp, e.g. containing sodium and mercury vapours and argon or xenon, has a tubular envelope of translucent alumina closed at each end by an alumina endcap. Alumina tube 11 (Fig. 1, not shown) is mounted on stiff lead wires 7 and 9 within an evacuated glass envelope 1, the alumina end caps 13 of tube 11 each having a central tapered aperture for the receipt of the tapered shank of a molybdenum electrode lead which supports an emissive tungsten helix (Fig. 2, not shown). The end caps may be shaped as in Fig. 12 to ensure, during operation, a lower temperature for the seal 77, 78; alternatively, a loose fitting alumina plug may be mounted on the cap end of the electrode (Fig. 11, not shown). The electrode leads are sealed through the end-caps by coating with calcium oxide and heating, and the end caps to the tube 11 either by coating with calcium aluminate and heating, or, without coating, by heating to a higher temperature. The electrodes may, alternatively, extend through the wall of tube 11; a starting probe may be included adjacent one of the electrodes; and outer envelope 1 may be dispersed with by grafting on to the end caps protective sleeves for the electrode leads. The lamp is manufactured by mounting it in a bell jar connected to a vacuum pump and argon supply and resting on a base plate through which pass a plurality of water-cooled plungers which permit the manipulation of the end caps relative to the tube 11, and the traversal along the length of the tube of an electric resistance heater for degassing the tube, and sealing the end-caps thereto, while argon at a pressure of 20 mm. mercury is flowing through the bell jar (Figs. 3 to 7, not shown). Before the tube is sealed, the cup of sodium 73, Fig. 10, is moved into it and the sodium distilled off; cup 73 is then disengaged from hook 72, and the radially resilient end of tube 71 lowered to pass over, grip, and raise the mercury-containing funnel 74, the lower end of which is drawn to a capillary, the mercury thereafter being blown out through the capillary into tube 11 by admitting a burst of inert gas through the hollow plunger 70. The tube 11 may be held either vertically or horizontally in the bell jar, the two end caps being sealed on simultaneously in the latter case.