GB952938A - Improvements in or relating to incandescent electric lamps - Google Patents

Abstract

952,938. Incandescent electric lamps. GENERAL ELECTRIC CO. Ltd. Aug. 13, 1962 [Aug. 16, 1961], No. 29576/61. 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 of at least 0.01 micromole per c.c. of envelope volume and mercury in an atomic ratio to the iodine greater than 1: 2 and sufficient to produce at operating temperature, in conjunction with the iodine vapour, an internal pressure of at least one atmosphere, the shape and dimensions of the envelope in relation to that of the filament being such that the temperature of the interior surface of the envelope lies everywhere within the range 250-1200‹ C. at the operating temperature of the filament. Iodine in excess of 0.01 micromole per c.c., e.g. sufficient to produce a vapour pressure of one atmosphere at the boiling-point of iodine may be used. The mercury present may be sufficient to produce the saturated vapour pressure of mercury at the operating temperature. A filling of inert gas up to e.g. a pressure of one atmosphere may also be present. The envelope may be of quartz, silica glass or of a transparent or translucent refractory material. In the form shown, the filament 4 of tungsten is extended by tungsten wires 5 into the pinches 3 at the ends of a tubular quartz envelope 1, the wires 5 being welded to molybdenum foil strips 6 connected to platinized molybdenum leads 7. The ends of the envelope surrounding the pinches 3 are coated externally with a thin layer of platinum 8. The filling consists of argon, iodine and mercury, the last two being supplied by introducing mercuric iodide and mercury through a side tube 9 which is then sealed off. An envelope of spherical form may be used. The Provisional Specification describes a tubular lamp with the ends of the envelope surrounding the pinches coated internally with a thin layer of platinum, and refers to the addition of a small quantity of chlorine or bromine to the filling. Specification 952,938 is referred to.