GB1060350A - Improvements in or relating to high pressure mercury vapour electric discharge lamps - Google Patents

Abstract

1,060,350. Discharge lamps. CLAUDE PAZ ET VISSEAUX. Nov. 23, 1965 [Nov. 25, 1964; Sept. 21, 1965], No. 49671/65. Heading H1D. A high pressure discharge lamp has a filling of mercury, rare gas and a mixture of halides comprising at least one halide of each of the metals indium, thallium and gallium, the halides, and preferably also the mercury, being present in amounts such that the vapour thereof is in the unsaturated state under normal operating conditions of the lamp. The halide mixture preferably comprises, by weight, 20 to 50% of indium iodide, 20 to 40% of thallium iodide, and 10 to 50% of gallium triiodide, the total quantity of halides being no more than 6 mg. per c.c. of the discharge space. Specific examples are given for a particular lamp containing 25 mg. of mercury and argon at 20 mm. of Hg pressure at 15‹ C. The excess of iodine due to the triiodide prevents deposition of tungsten from the electrodes on the tube wall, and may combine with metallic thorium present in the electrodes forming thorium iodide which contributes to the light emission. The mercury may be introduced in the form of mercury iodide, and one of the metals In, Tl and Ga may be introduced in the form of a plurality of halides. A halide of a further metal may also be present. The discharge lamp is mounted in, and thermally insulated from, an outer envelope which may be of yellow glass, or may be coated with a yellow pigment or a fluorescent material, e.g. magnesium fluorogermanate or zinc and strontium orthophosphates activated with tin.