GB834087A - Improvements in or relating to electric incandescent filament lamps - Google Patents

Abstract

834,087. Electric incandescent lamps. GENERAL ELECTRIC CO. Ltd. Sept. 23, 1958 [Sept. 23, 1957], No. 29835/57. Class 39(2) In an electric incandescent lamp, the filament is at least partly surrounded by a multi-layer interference filament transparent visible lght and reflecting infrared radiation, the filter being so disposed that light from the filament is incident thereon substantially perpendicularly to the surface so that the major portion of the infra-red radiation is reflected back towards the filament. The filter may have from 5 to 25 separate layers and be formed with a sharp cut-off at the long-wave end of the spectrum. In the form shown, a straight helical filament 3 is enclosed in a tubular envelope 1 of quartz and is supported by spiral coils 4 of tungsten wire. The envelope 1 is filled with Argon at 600 mm. pressure, contains a regenerative getter such as iodine vapour, and is enclosed in an outer glass jacket 7 which is sealed and evacuated. A multi-layer interference filter 13 is carried on a glass sleeve 12 surrounding the tube 1. Alternatively the sleeve may be omitted and the filter may be mounted on the outside of the tube 1 or on the inner surface of the jacket 7. In a further modification the filter is applied to the inner surface of a cylindrical glass tube mounted inside the envelope 1. Alternatively, the filter may be provided on a lamp fitting carried by a support having supply terminals for the lamp, the lamp envelope with or without a removable outer jacket being mounted in the fitting.