GB852783A - Improvements in or relating to high pressure mercury vapour electric discharge lamps - Google Patents

Abstract

852,783. Fluorescent discharge lamps. GENERAL ELECTRIC CO. Ltd. June 24, 1959 [June 3, 1958], No. 17703/58. Drawings to Specification. Class 39(1). A high pressure mercury vapour electric discharge lamp of the kind having a quartz discharge envelope mounted within a glass outer jacket, wherein W/1, where W is the wattage and 1 the arc length, lies between 40 and 100 W. per cm., and the discharge envelope is of such shape that the external wall temperature lies everywhere between 580‹C. and 650‹C.; and the metal filling inside the lamp includes a quantity of zinc in such proportion that when the lamp is operating at W watts from an alternating supply the voltage drop per cm. of arc length is between 10 and 35, and the number of burners emitted at wavelengths between 4600Š and 5100Š is not less than 2% of the total light output of the lamp ; and the discharge envelope is surrounded by a screen coated with a red fluorescing phosphor of such thickness that the number of lumens emitted at wavelengths between 6100Š and 7200Š is not less than 5% of the total lumen output of the lamp ; the proportion of zinc filling, e.g. the lamp contains 80 mgm. of mercury and 40 mgm. of zinc and the thickness of the phosphor layer being, however, so small that the initial luminous efficiency of the lamp is not less than 40 lumens per watt. The outer glass jacket may be ovoidal and the inner quartz envelope 94 mms. long, containing directly heated electrodes formed from a tungsten rod containing a slot in its side, the slot contains an electron-emissive pellet which is held in place by a tungsten helix the electrodes are spaced 800 mms. apart and an auxiliary electrode is set in the wall near one end of the tube. The innermost parts of the seals of the tube are coated with platinum to reduce ' cold-spot ' effects and the tube is filling with argon at 20 mm. to act as a starting gas and the space between the envelopes is evacuated. The wall temperature is measured by means of a thermo-couple. The red phosphor may consist of magnesium fluor-germinate or magnesium arsenate activated by 0À15% of manganese or of [1À2 BaO, 1À2 SrO, 0À6 Li 2 O, 1À9 SiO 2 ] activated with 10% cerium and 1À2% manganese, which is coated on a quartz sleeve snugly fitted round the discharge envelope. The Provisional Specification states that the phosphor may also comprise a combination of magnesium arsenate and magnesium fluoro-germinate, activated by manganese.