GB790959A - Improvements in or relating to low-pressure arc discharge tubes - Google Patents

Abstract

790,959. Discharge lamps. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Feb. 23, 1956 [Feb. 26, 1955], No. 5645/56. Class 39(1). A low pressure arc discharge tube, particularly a fluorescent lamp, containing mercury and a rare gas at a pressure of 1-6 mms. at room temperature, e.g., argon at 3À5 mms., comprises two electrodes 10 and 11, at least one 10 of which is an activated thermionic electrode, of which the enveloping surface is a cylinder and which is surrounded, with a spacing of 0À5-1À5 mms., by a molybdenum cylinder 12 of 10- 30, preferably 20, microns wall thickness connected to the electrode 10 by a tag 13 and a wire 14, and also comprising at least one conductive coating 5, particularly in the form of a graphite strip on a layer of luminescent material, which coating extends through at least half the length of the tube and is insulated from the thermionic electrode 10 and connected to the other electrode 11 by a piece of wire 16 and a metallic strip 17 in the form of a quarter of a circle. The cylinder 12 can have an inner diameter of 4 mms. and a length of 8 mms. The supports 6 and 7 of the electrode 10 are connected outside the tube to a terminal 15 and the support 9 for the electrode 11 is connected to a terminal 18. The tube can comprise two activated thermionic electrodes and only one strip coating 5, with only the thermionic electrode which is insulated from the coating being provided with the cylinder 12. Reference is also made to a thermionic electrode 11 also surrounded by a molybdenum cylinder connected to the supporting wire 8. Tests are referred to with cylinders 12 of chrome-iron, nickel, iron, tantalum and zirconium of up to 100 microns thickness.