Patent GB-766150-A (GB)
Title: Improvements in or relating to low pressure fluorescent electric discharge lamps
IPC: H01J61/42
Filed: 1952-11-20
Abstract: 766,150. Fluorescent discharge lamps; luminescent materials. GENERAL ELECTRIC CO., Ltd., and JENKINS, H. G. Nov. 20,1953 [Nov. 20, 1952], No. 29365/52. Class 39(1). A lamp/filter combination is of the kind in which the lamp is a low pressure mercury vapour fluorescent discharge lamp of the positive column type the tubular glass envelope of which is coated with a main fluorescent material excited by the short wave U.V. radiation from the discharge so as, in conjunction with the visible radiation from the discharge, to emit a main light which has a substantially white appearance, and the filter is designed to reduce selectively the intensity in the main light of radiation of wave lengths 4047Š and 4358Š, and wherein the filter consists of a layer of zinc cadmium sulphide carried on or in a transparent or translucent supporting means and arranged and activated so as to be excited to luminescence by the long wave U.V. radiation from the discharge and so that the main light passes through the layer, the arrangement being such that the resultant light resembles that emitted by a tungsten filament at a temperature in the range of 2000‹K to 3000‹K. The zinc cadmium sulphide can be provided as a coating on the inner wall of the envelope and the main fluorescent material provided as a further coating on top of the zinc cadmium sulphide. A coating of a stable light-diffusing white material, such as one or more of finely powdered calcium helophosphate, silica, alumina, magnesia or titania, may be provided on the wall of the envelope underneath the coatings of the zinc cadmium sulphide and the main fluorescent material. In a modification the filter has the form of a transparent sleeve coated or impregnated with the zinc cadmium sulphide and fitted over the lamp envelope, or as part of a fitting in which the lamp is mounted. The grain size of the zinc cadmium sulphide is about 5Á and the coating density about 0À50 to 0À75 mgrs. per sq. cm. The grain size of the lightdiffusing white coating is about 3 Á and the coating density about 1À0 to 1À5 mgrs. per sq. cm. The zinc cadmium sulphide can be activated by copper, gold or silver or can be self-activated and can have a matrix composition within the range of, by weight, 80 per cent zinc sulphide: 20 per cent. cadmium sulphide to 60 per cent. zinc sulphide: 40 per cent. cadmium sulphide, preferably 70 per cent. zinc sulphide : 30 per cent. cadmium sulphide. The main fluorescent material consists of one or more phosphors fluorescing red, orange or yellow under excitation by short wave U.V. radiation of wave length 2537A and selected from magnesium arsenate activated by manganese, cadmium borate activated by manganese, calcium orthophosphate activated by cerium and manganese, magnesium fluorogermanate activated by manganese, calcium, metasilicate activated by lead and manganese, calcium helophosphate activated by antimony and manganese, zinc beryllium silicate activated by manganese, and zinc borate activated by manganese, together with one or more phosphors fluorescing blue or green under excitation by short wave U.V. radiation of wave length 2537Š and selected from magnesium tungstate, calcium tungstate with or without lead activator, barium or strontium pyrophosphate activated by tin, zinc orthosilicate activated by manganese and calcium halophosphate activated by antimony. Proportions of activators are given in several specific examples.