GB666470A - Improvements in electric discharge lamp circuits - Google Patents

Abstract

666,470. Control systems for space discharge lamps. THORN ELECTRICAL INDUSTRIES, Ltd., STRANGE, J. W., WAIGH, D. T., and BLOXSIDGE, W. R. Sept. 13, 1949 [July 6, 1949], No. 6591/51. Divided out of 666,403. Class 38 (iv). The dimming of an electric discharge lamp L1 having filamentary electrodes E1, E2 and supplied through a ballast impedance B is effected by a variable auto-transformer F<SP>1</SP>2, the secondary W7 of which is in series with the ballast and lamp, whilst the heating of the electrodes is effected through a high reactance transformer W1 having secondary windings W2-W4 connected to the lamp electrodes and the primary connected across the secondary winding of the auto-transformer through a condenser C2 of value such that at a voltage across the secondary winding W7 just below the lamp striking voltage the primary circuit of the heating transformer is at resonance thereby providing maximum heating current. An " earthed " external auxiliary electrode S1 may be provided to improve starting. Each lamp circuit may comprise two or more series connected lamps heated from one transformer and with a single dimmer controlling a number of such circuits. To obtain the same illumination each junction between the series connected lamps may be connected through a resistance R2 and condenser C1 to the neutral supply lead N. Two or more parallel connected lamps may be operated from a single auto-transformer, Fig. 2 (not shown). The Provisional Specification refers to Specification 666,403.