Patent GB-836552-A (GB)
Title: Improvements in or relating to electric discharge lamps
Inventor: NELSON EVAN HERBERT
IPC: H01J61/24
Filed: 1955-08-09
Abstract: 836,552. Discharge lamps. GENERAL ELECTRIC CO. Ltd. July 18, 1956 [Aug. 9, 1955], No. 22957/55. Class 39(1). [Also in Group XXIII] An alkali-metal vapour discharge lamp containing a rare gas for starting and having an envelope formed of, or coated on its inner surface, with a glass which is substantially free from attack by the alkali-metal vapour, has included within and closely adjacent the wall of the envelope one or more reservoir members of relatively small cross-section, each of which is capable of absorbing metal from the metal vapour present and of releasing some of the metal when the vapour pressure in the region of the member falls, and the member or members either extending over at least the greater part of the length of the discharge path, in the case of a single member, or being spaced apart along the length of the discharge path in tne case of a plurality of members. Each reservoir member can be formed of a glass which readily absorbs the vapour of the alkali metal, and having the percentage composition by weight : CaO-6, SiO 2 -8, Na 2 O-14, Al 2 O 3 -24, B 2 O 3 -48. Alternatively the reservoir members may be of ceramic material. Each reservoir member can consist of a glass rod formed into a helical coil just fitting within the envelope. A single reservoir member so formed can extend along substantially the whole length of the discharge path. In the construction shown in the drawing the envelope 1 is U-shaped and a helical glass rod 22 is contained within each limb 2 of the envelope, and the envelope is provided with one or more indentations 23 forming shoulders for positioning the rods 22. Each helical rod 22 can be in contact with the envelope for substantially the whole of its length so that part of the alkali metal is retained at each turn by surface-tension as described in Specification 836,551. Alternatively the helical rods 22 can be held in place by glass solder. Each limb 2 of the envelope is provided with a closely fitting tubular glass sleeve 15 as described in Specification 810,482. The sleeves 15 are held in position by a tubular glass bush 16 and a mica sheet 17. The curved end of the envelope 1 is supported within an outer jacket 5 by a wire 18 passing through the bush 16 and two D-shaped split rings 19 welded one to each end of the wire 18. Rotation of the support means is prevented by two wires 20 attached to the electrode leads 4, passing through slots in the mica sheet 17, winding helically around the sleeves 15 and attached to mica tags carried by the split rings 19. The wires 20 can act as starting electrodes. The space between the envelope 1 and the jacket 5 is exhausted and contains a getter element 13 welded to a support wire 14. The alkali-metal vapour can be sodium, caesium or potassium and the rare-gas filling can be neon containing 0À5% by volume of argon at a total pressure of 10 mms. In another construction the reservoir members can consist of a multiplicity of short glass rods spaced substantially uniformly along the envelope and held in abutment with the envelope by spring members or attached to the envelope by glass solder. On a further construction each reservoir member can be in the form of a coating on the envelope when this consists of an alkaliresistant glass or on the internal coating of alkali-resistant glass.