GB829286A - Improvements in or relating to sodium vapour electric discharge lamps - Google Patents

Abstract

829,286. Discharge lamps. GENERAL ELECTRIC CO. Ltd. May 17, 1956 [May 31, 1955], No. 15604/55. Addition to 801,482. Class 39(1). [Also in Group XXIII] A sodium vapour-rare gas discharge lamp having a U-shaped envelope sealed into a singlewalled highly evacuated outer jacket and with each limb, of circular or non-circular section, of the envelope closely surrounded by a sleeve of transparent heat-insulating material as described in the parent Specification, has at least one sleeve formed wholly or partly of a material which is highly transparent to the visible radiations of 5890Š and 5896Š wave length emitted by the sodium vapour discharge, but which is such that the proportion of the incident infrared radiations from the discharge which is directly transmitted through the sleeve is appreciably less than the proportion which would be directly transmitted through a sleeve of the same dimensions formed wholly of soda glass having the composition in percentages by weight : SiO 2 -70-0, Al 2 O 3 -2À5 CaO-5À5, MgO- 3À5, Na 2 O-17À0, K 2 O-0À4, B 2 O 3 -0À8, SO 2 -0À2. The or each sleeve can be wholly or partly formed of a phosphate glass having the composition in percentages by weight : P 2 O 5 -67À44, Al 2 O 3 -13À44, CaO-7À12, B 2 O 3 -5À00, SiO 2 -5À00, Fe 2 O 3 -2À00. The phosphate glass manufactured by Chance Bros. Ltd. known as ON20 may also be used. Each sleeve may-consist of a cylinder of glass such as the aforesaid soda or phosphate glass coated on one or each surface with a thin film which is highly transparent to the yellow sodium light but which has a high absorption and/or reflection factor for infra-red radiations. The film may consist of copper, gold,- titanium dioxide or stannic chloride formed by thermal evaporation, sputtering or chemical decomposition. The sleeves may be slid on to the limbs of the U-envelope and held in position by means which restrain the sleeves against relative longitudinal displacement but without the sleeves being attached to the limbs and without the intervention of spacing means ; alternatively the sleeves may be attached to the limbs at one or more regions whose total axial length is small compared with the axial length of the limbs. The sleeves can be used in the specific constructions of lamp described in the parent Specification.