GB952937A - Improvements in or relating to incandescent electric lamps - Google Patents

Abstract

952,937. Electric incandescent lamps. GENERAL ELECTRIC CO. Ltd. Aug. 13, 1962 [Aug. 16, 1961], No. 29575/61. Heading H1F. Lamps in which the pressure within the envelope at operating temperature is at least as high as one atmosphere, comprise a filament of tungsten free from impurities other than the usual additives for modifying the crystal structure, in an envelope of light transmitting heat resisting material and having a filling of iodine exceeding 1.0 micromole per c.c. of envelope volume, the shape and size of the envelope and the filament being such that the interior surface of the envelope lying between two planes at right-angles to the envelope axis, between which the length of the filament extends is heated to 800-1200‹ C. when the filament is heated to 2900-3500‹ K. by the passage of electric current. The iodine content may be 27 micromoles per c.c. or more up to the point where the iodine vapour pressure is saturated at the temperature of the coolest part of the envelope. Mercury and an inert gas up to a pressure of one atmosphere may be included in the filling. The envelope may be in the form of a tube of bore less than four times the filament diameter or alternatively a spherical envelope may be used. The external surface adjacent the pinch or pinches may be coated with a layer of metal of high heat reflectivity, e.g. platinum. The envelope may also be enclosed in an outer jacket having a heat-reflecting film on its inside surface. In the form shown, the filament 4 of tungsten extends between leads 5 of tungsten united within the pinches 3 to strips of molybdenum foil 6 welded to lead-in wires of platinized molybdenum 7. The envelope 1 is a small bore tube 1 of quartz, the iodine filling being inserted through a side tube 8 which is subsequently sealed off. Specification 952,938 is referred to.