GB404101A - Improvements in or relating to electric discharge tubes - Google Patents

Abstract

404,101. Electric lamps. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, 13D, Emmasingel, Eindhoven, Holland. Oct. 3, 1932, No. 27416. Convention date, Oct. 3, 1931. [Class 39 (ii).] An electric discharge lamp comprises an outer envelope 13, Fig. 1, enclosing an inner envelope 1 containing a pair of electrodes 2, 3 arranged a short distance from a quantity of vaporizable metal such as a pool of mercury 8, the space between the envelopes 1, 13 forming an enclosure for a heating-element 12 disposed at such a short distance below the metal 8 that a continuous vaporization is produced, causing a contracted arc discharge between the electrodes to be curved strongly upwardly, as indicated by the dotted lines 28. Preferably the distance between the electrodes is greater than 1 cm. and the length of the contracted arc discharge 1.25 times that distance. In the example the electrodes 2, 3 consist of helically wound wires coated with electron-emitting material such as barium oxide, each electrode being provided with a pair of pole wires sealed within extensions 5 from the vessel 1. The heating element 12 comprises a helically wound filament supported by wires projecting radially from a boss 11 at the bottom of a glass stem 10 sealed at the lower portion of the vessel 1. One end of the filament is connected bv a wire 18 to the lamp cap contact 22, the other end being connected by a wire 17, Fig. 3, to the junction of the pole wires of the electrode 3. The pole wires of the electrode 2 are connected by a conductor 19 to the leading-in wire 20 from the cap 21. To facilitate starting, an auxiliary electrode 9 dipping into the mercury pool 8 is connected, through a high resistance 25 having a value of 1000-10,000 ohms, to the wire 17. In addition to the mercury 8 the discharge tube 1 contains a rare gas such as argon which, at room temperature may have a pressure of 0.1-20 m.m. The space between the inner and outer bulbs is filled with an inert gas or vapour at a pressure lower than atmospheric, and a mica screen 26 is mounted on the pinch 15 to protect that member from the heat radiated by the discharge tube. The bulbs may be made of material which is transparent to ultra-violot rays, the inner bulb preferably being substantially spherical to prevent undesired condensation of the metal vapour due to dead spaces.