Patent GB-801482-A (GB)
Title: Improvements in or relating to sodium vapour electric discharge lamps
Inventor: RIGDEN SYDNEY ALFRED RICHARD
IPC: H01J61/34
Filed: 1954-01-27
Abstract: 801,482. Discharge lamps. GENERAL ELECTRIC CO., Ltd. Jan. 27, 1955 [Jan. 27, 1954; July 12, 1954]. Nos. 2517/54 and 20306/54. Class 39(1). A U-shaped sodium vapour lamp supported within an evacuated single-walled outer jacket has one or more sleeves of transparent or translucent heat-insulating material fitting closely (as defined) around each limb of U-shaped lamp. In the construction shown in Fig. 1 of the drawing accompanying the first Provisional Specification the glass sleeves 16 are a loose fit on the limbs 2 but are prevented from longitudinal movement by the stops 8<SP>1</SP> comprising wires welded to the electrode mounting wires 8, and the wire loop 14 surrounding the two limbs 2. Spacing means may be employed for holding the sleeves coaxially on the limbs 2. The curved end of the envelope 1 is supported centrally within the outer jacket 4 by a length of wire 12 passing through a glass bush 13 and welded to the loop 14, the two ends of the wire being welded to curved metal plates 15 bearing against the inner surface of the jacket 4. The other end of the envelope 2 is supported by the mounting wires 8 passing through a mica disc 17 supported by a wire 18 sealed into the pinch 9. To aid starting a nickel wire is connected to each of the electrode leads 7 and helically wound round the glass sleeves 16 and insulatingly attached to the support for the curved end of the discharge envelope 1. Operating characteristics and dimensions are stated and the internal diameter of each sleeve 16 can be not more than 2 mms. greater than the external diameter of the corresponding limb 2. Each sleeve 16 can be surrounded by one or more further closely fitting transparent heat-insulating sleeves and the internal diameter of each further sleeve can be not more than 2 mms. greater than the external diameter of the sleeve it surrounds. The filling consists of neon containing 0À5 per cent by volume of argon at a total pressure of about 10 mms. of mercury, together with about 1 gram of sodium. The jacket 4 is evacuated by placing it together with the discharge envelope 1 in an oven and heating it by hot air to between 100C. and 125C., evacuating it to a pressure of about 10-4 mms. with an exhaust pump, disconnecting the jacket from the pump, filling it with dry oxygen-free nitrogen at a pressure of 10-20 mms., raising the temperature to 365C., reconnecting the jacket to the pump, repeating the operations at a temperature of 365C., allowing the jacket to cool to about 100C. and sealing it. A getter element 19 attached to the wire 18 is then heated to cause getter material to evaporate and condense on the wall of the jacket. In the construction shown in Fig. 1 of the drawing accompanying the second Provisional Specification each glass sleeve 16 is sealed to a pinch 24 at the end of the corresponding sleeve 2 and the electrode leads 7 pass through holes in the mica disc 17 and are connected to the mounting wires 8 by welded nickel sleeves 20. Other elements are provided as in the previous construction. One or more additional transparent heat-insulating sleeves 16 can be fitted loosely over the sleeves 16 or attached to the sleeves 16 and to the envelope 1. Each sleeve can be attached to a limb 2 at one or more regions whose total axial length is small compared with the axial length of the limb. Each sleeve can be of a glass whose thermal expansion coefficient is similar to that of the glass of the discharge envelope and is sealed to the pinch formed at the end of the corresponding limb. Specification 731,694 is referred to.