Patent GB-770343-A (GB)
Title: Improvements in or relating to colour corrected electric discharge lamps
IPC: H01J61/42
Filed: 1954-11-25
Abstract: 770,343. Fluorescent discharge lamps; luminescent materials. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Nov. 25, 1954 [Dec. 3, 1953], No. 34174/54. Class 39(1). A H.P.M.V. lamp, an electric discharge lamp, particularly has an outer glass bulb 54 the inner surface of which is coated internally firstly with a silver reflective layer 56, then with a layer 58 of silica and then with a layer 60 of a phosphor. The phosphor may be diffused throughout the silica so that the phosphor is substantially separated from the silver layer by a layer of silica. The face portion 12 of the bulb 54 may be clear, frosted or carry a silica coating. The phosphor may be magnesium germancle or arsenate or fluorogermanate or a blend of 40 per cent. magnesium fluorogermanate, 40 per cent. calcium-strontium silicate and 20 per cent. calcium fluorophosphate. The silver layer may be about 0À0005 of an inch thick. The silica layer may comprise pure silica powder or a powder comprising 96 per cent. by weight silica, 3 per cent. by weight calcium oxide and 1 per cent. by weight sodium chloride. The average particle size of the silica may be about 0À2 to 0À6 micron. The upper limit of the average particle size of the silica should not be greater than the wave length of the lamp radiation, i.e. about 2500 A.V. to about 7000 A.V. The thickness of the silica coating may vary from 0À4 to 22 mgrs. per sq. inch. The silica is suspended in a vehicle such as butyl alcohol, ethyl alcohol, amyl alcohol or acetone before application to the reflective layer. In one example 36 grs. of silica was suspended in 200 c.cs. of butyl alcohol. The phosphor may be applied by a suspension of 75 grs. of phosphor in 100 grs. of butyl alcohol. The phosphor layer may be 10 mgrs. per sq. inch. The power input to the discharge tube 18 should be of such magnitude with respect to the size of the bulb 54 that the bulb operates within the most efficient operating temperature range of 150‹C. to 400‹C, of the phosphor. The discharge tube 18 comprises a quartz envelope 20, main electrodes 22, 24 consisting of a tungsten wire having an overwind of tungsten wire within which is a small amount of thorium to facilitate starting, and an auxiliary tungsten wire electrode 26. The tube 18 is supported within the bulb 54 by frame wires 28 and 30 supported at one end by a frame 32 and at the other end by a plurality of resilient strips 34. The frame 28, 30, 32 can be of nickel plated iron and the strips 34 of a nickelcobalt-aluminium-titanium alloy. Retaining plates 36 and retaining strips 38 are provided. The tube 18 contains argon at a pressure of about 20 mms. to facilitate starting and a quantity of mercury to provide an operating pressure of about 2À5 atmospheres with a power consumption of about 400 watts. The space between the tube 18 and the bulb 54 contains nitrogen at a pressure of 500 mms. Coppernickel lead-in conductors 44, 46 are sealed through the press 50 of the flare tube 40 and may have a nickel core with a copper coating at those portions which pass through the press in order to facilitate sealing. One lead-in conductor 44 is connected to the frame 32, and the other lead-in conductor 46 is connected to the electrode 22 through a nickel conductor. The electrode 24 is connected to the frame wires 28, 30 through a nickel conductor and the auxiliary electrode 26 is connected to the frame wires 28, 30 through a 15,000 ohm 15 watt resistor 52. Molybdenum sealing ribbons 53 are provided for the lead-in conductors.