Patent GB-493360-A (GB)
Title: Improvements in high-pressure mercury-vapour electric-discharge lamps
IPC: H01J61/82
Filed: 1937-04-05
Abstract: 493,360. Discharge lamps. GENERAL ELECTRIC CO., Ltd., FRANCIS, V. J., and RYDE, J. W. April 5, 1937, Nos. 9634 and 11398. [Class 39 (i)] In a high-pressure mercury vapour lamp having an envelope of quartz or of a material not more refractory than quartz (i) the power W dissipated in the discharge when in full operation lies between 150 and 1000 watts (ii) the length l of the discharge column in full operation is not less than 2 cm, (iii) the initial efficiency measured in lumens per watt is not less than given by curve 2, Fig. 4, (iv) the factor M by which the efficiency falls off over a life of 1000 hours is not less than 0À6 and (v) the ratio of W to the internal surface area of the envelope lies between 7 to 35. da Is the average diameter of the envelope containing the discharge at that part where the discharge takes place and VT is the R.M.S. potential across the main discharge when in full operation. Figs. 5, 6 and 7 show the relationship between W, l, da and VT for a value of VT of 160. To obtain the sizes for other voltages an equation #=0À5+0À003VT is used to give the change factor ; whence if da‹l‹ are taken from Figs. 5, 6 or 7, then the new da=da‹.# and l=#l‹. The initial efficiency is that obtained when the lamp is first run before there is any substantial falling off in performance. VT is not less than 80 volts. The lamp is not cooled except by air flow which may be directed by chimneys and vanes ; cooling ribs maybeprovided. Reflecting coatings may be used on the interiors at the ends to maintain temperature conditions. The discharge envelope may be enclosed in an outer shell the inter-space being evacuated or filled with air at atmospheric pressure or nitrogen at ¢ an atmosphere. Luminescent materials may be placed outside the discharge envelope and these materials may emit green or blue light. Particular constructions of lamps with dimensions obtained from the diagrams are described ; these are shown as having vertical discharges. If horizontal discharge lamps are constructed magnetic means may be used to prevent bowing of the arc. In these lamps each main electrode-if the lamp is to run on A.C.-is formed with starting and running electrodes of the kind described in Specifications 392,509 and 444,545, that is a starting section having readily emitting material such as barium or strontium and an unactivated running portion ; the latter may be a tungsten rod 7, Fig. 12, surrounded at the end remote from the main discharge by three spirals 8, 9, 10 inside which is a rod 11 of barium-strontium silicates as described in Specifications 384,067 and 411,266. The main discharge starts up on the activated portion and transfers itself to the tungsten rod 7 ; auxiliary electrodes to start the discharge may also be used, and the starting and running parts of the main electrodes may be independently constructed. For D.C. running only one main electrode need be constructed as described. The lamps are intended for use on mains subject to a 6 per cent variation in voltage above or below normal, and using a reactive stabilizing impedance ; the circuits may be of the kind described in Specifications 486,586 and 491,071, [both in Group XXXVI]. A series resistance may form an integral part of the lamp. The lamp runs subsaturated with a mercury filling, to which gases may be added to facilitate working. Specifications 472,658, 485,274, and 485,489 also are referred to.