GB914650A - Improvements in or relating to sodium vapour electric discharge lamps - Google Patents

Abstract

914,650. Discharge lamps. GENERAL ELECTRIC CO. Ltd. Jan. 2, 1961 [Jan. 7, 1960], No. 622/60. Addition to 865,928. Class 39 (1). [Also in Group XXIII] A low-pressure sodium vapour-rare gas discharge lamp envelope 1, which can be straight or U-shaped, has in the region between the electrodes at least one axially straight part formed with a plurality of flattened regions 22 of relatively long axial length separated by intermediate regions 23 of relatively short axial length having a substantially circular crosssection, the flattened regions each having an area of cross-section between one quarter and three quarters that of the intermediate regions and having in each cross-section of the region a maximum diameter which is not less than the diameter of the intermediate regions as in the parent Specification, and each intermediate region including a recess 25 formed within the envelope by the outwerd deformation of part of the envelope wall. Each of the recesses is substantially cup-shaped and has an internal diameter at the wider end equal to or greater than the internal radius of the intermediate regions of the envelope, and a depth which is at least equal to the radius of the recess at its wider end. The internal diameter of the intermediate regions can be approximately 15 mms., the internal diameter of each recess at the wider end can be approximately 8 mms., and the depth of each recess can be approximately 6 mms. When the envelope is of U- shape the recesses 25 can be provided on the parts of the limbs of the U facing outwards. The envelope or an internal coating on a soda-glass envelope can be formed of a sodium-resistant glass, e.g. a borate glass of specified composition. A method of making the envelope is described. The envelope can be mounted within an evacuated single-walled outer jacket 3 and each limb of the envelope can be surrounded by a sleeve 12 of transparent heat-insulating material which fits closely around the limb and extends substantially the whole length thereof. Alternatively both limbs can be surrounded by a single sleeve. In another construction the envelope is detachably mounted within a double-walled outer jacket with air present between the envelope and the jacket. The outer surface of the curved end of the envelope can be coated with a layer 26 of heat-reflecting material such as silver or platinum paint. The envelope is filled with neon containing approximately 1.0% argon and 0.02% xenon at a total pressure of about 10 mms. and contains sodium. The discharge envelope 1 and sleeve 12 are mounted within the jacket 3 by the mica disc 9, spring member 13 and spring clip 17. The mica disc 9 is held in position within the envelope by a pair of metal starting wires 15 wound helically around the sleeves 12 and connected to a mica tag 16 carried by the clip 17. The jacket 3 contains a getter element 20 connected to one of the electrode mounting wires 6.