GB1056894A - High pressure electric discharge lamps - Google Patents

Abstract

1,056,894. Metal-vapour lamps. SYLVANIA ELECTRIC PRODUCTS Inc. Sept. 21, 1964 [Oct. 1, 1963], No. 38459/64. Heading H1D. A high pressure discharge lamp with a filling which includes both halogen atoms and mercury atoms, has a cylindrical envelope formed at each end with a well of reduced diameter, the two electrodes-each constituted by a wire helix mounted upon a rod-being disposed within the wells, and each extending from within its well towards the centre of the tube at least to the mouth of the well. The electrode rods 5 and 6 (Fig. 1, not shown) of the electrodes disposed within the wells 12 and 14, and auxiliary electrode rod 7, pass through the press seals 1 and 2, the width of each of which is not more than twice the diameter of a well, and which may have thickened edges 15 and conical shoulders (Fig. 2, not shown) at the join with the tubular envelope 18. The rear of each electrode helix 3, 4 is spaced from its well base by 0À5 to 1À5 mm., and its forward end is at least flush with the well mouth, and may extend beyond it. The well diameter is 3 to 4 times the helix diameter, or more if the external well wall has a reflective gold coating (Fig. 2, not shown) to raise the temperature of, and thereby prevent condensation in, the well. A filling of mercury, iodine, thorium, and argon is referred to, in which the ratio of iodine to mercury atoms lies between 0À1 and 0À85; sodium may also be added, to the amount of 5À2 x 10<SP>-7</SP> to 1À6 x 10<SP>-5</SP> gm. atoms per centimetre of arc length (55 m.m.s.). The thorium and the sodium may each be added either as metal or as iodide.