GB669888A - Improvements in and relating to electric discharge lamps - Google Patents

Abstract

669,888. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. April 24, 1950 [April 30, 1949], No. 10035/50. Drawings to Specification. Class 39 (i). In an ultra-violet discharge lamp for germicidal use having a sealed envelope consisting of glass formed by heating the glass batch under reducing conditions difficulty in starting the lamps after long storage is prevented by adding a thin adherent film of antimony trioxide (Sb 2 O 3 ) on the inner surface of the envelope. The film may be deposited by flushing the tube with a suspension of antimony trioxide in a mixture including nitrocellulose and butyl acetate. The glass may be alkali-aluminaborosilicate hard glass or soft glass within the following proportions by weight: SiO 2 +B 2 O 3 , 60-74 per cent, the B 2 O 3 not exceeding 5 per cent; Na 2 O+K 2 O+Li 2 O, 13-20 per cent; and BaO+MgO+CaO, 8-27 per cent, the Na 2 O and BaO being present singly or with one or both of the oxides specified. A good composition is SiO 2 , 65 per cent; B 2 O 3 , 2 per cent; Na 2 O, 9.5 per cent; K 2 O, 5.5 per cent ; and BaO, 18 per cent; a small quantity of aluminium being included in the glass batch to ensure any iron oxide impurity being in the ferrous form. The glass in a thickness of 1 mm. has a transmission for 2537 Š wavelength in excess of 40 per cent.