GB701072A - Improvements in or relating to electric discharge lamps - Google Patents

Abstract

701,072. Luminescent materials; discharge lamps. PHILIPS ELECTRICAL INDUSTRIES, Ltd., Jan. 3, 1952 [Jan, 6, 1951], No. 244/52. Class 39(1) An electric discharge lamp comprising a high pressure mercury vapour tube arranged within a hermetically seated bulb, that wall of the bulb which is adjacent the discharge tube being coated with a luminescent material and the space between the discharge tube and the bulb being filled with gas, is characterized in that the luminescent material is a reaction product activated by manganese and obtained by heat, which contains magnesium, arsenic and oxygen, the gram molecule ratio between magnesium oxide and arsenic pentoxide exceeding 3:1, and preferably being 9:1, as described in Specification 672,172, and in that the space between the discharge tube and bulb is filled with dry carbon dioxide or with a mixture of carbon dioxide and at least one of nitrogen and the rare gases, the pressure of the carbon dioxide being at least 0.2 cms., and may be 50 cms. of mercury. The content of manganese may range between 0.001 and 5 mol. per cent, and is preferably 0.1 per cent, based on the quantity of magnesium oxide, and the pressure of the gas contained in the space between the discharge tube and the bulb is preferably from 0.2 to 70 cms. of mercury. In the construction shown in the drawing the cylindrical high pressure mercury vapour discharge tube 1, which in normal operation has a wattage of 80, has an envelope of quartz, the internal diameter of which is about 8 mms., and contains activated electrodes 2 and 3 spaced apart by a distance of about 25 mms, and connected by molybdenum foil seals to current leads 5 and 4 led through a pinch 6 to the terminals of a bi-polar lamp cap. The pinch 6 forms part of a hermetically sealed, substantially spherical, glass bulb 7 having a diameter of about 80 mms. and coated with a layer 8 of the luminescent material. In normal operation the spherical part of the bulb 7 has a temperature of about 180‹C and those parts of the leads 4 and 5 which adjoin the seals have a temperature of about 400‹C.