GB191512994A - Improvements in and relating to Electric Arc Lamps. - Google Patents

Abstract

12,994. Mackay, G. M. J. Sept. 12, 1914, [Convention date]. Arc lamps.-A sealed bulb enclosing electrodes of refractory metal such as tungsten, contains mercury 11 or other vaporizing material which renders the arc luminous and diminishes disintegration of the negative electrode. The vapour pressure during working should be at least 150 mm. of mercury, but preferably about 1 atmosphere. An inert gas, such as nitrogen or argon, at a pressure of 150 mm. of mercury, may also be present; the mercury vapour drives the gas into the upper part of the bulb 1, which may be constricted at 12 to assist this action. At atmospheric pressure, an arc ¢ in. long may be maintained by an electric pressure of 25-35 volts, and an arc 1¢ in. long by a pressure of about 50 volts. Both electrodes are luminous. The energy-consumption in the arc per candlepower may be one-fifth of a watt or less. A steadying-resistance is formed by one or two incandescent filaments 7, 8, preferably of ductile tungsten and closely coiled, the vapour enabling a heavy current to be used. The lamp is preferably designed so that the resultant light is colourless. In an alternating- current lamp, the electrodes are formed by the adjacent ends of two filaments, or by beads 9, 10 thereon. Current is sent through both filaments by means of four leading-in wires until the electrodes are sufficiently heated, when the two outer wires are connected to the mains so that the arc and filaments are in series. In a direct-current lamp, only the negative electrode is attached to a filament, the positive electrode being carried by a single wire. To reduce loss of heat by conduction, the leading-in wires, which may be of drawn tungsten, are reduced in thickness near the electrodes. The wires diverge above the electrodes to prevent creeping of the arc. The bulb 1 and stem 6 may be of refractory lowexpansion glass, for instance sodium-magnesium boro-silicate, through which the tungsten wires may be directly sealed; or a silica or other bulb may be united to a glass stem, preferably of low-expansion, by a graded seal. Specifications 9226/04 and 17,326/14, [Class 39 (ii), Electric lamps, Incandescent], are referred to.