GB720264A - Improvements in operating circuits for electric discharge lamps - Google Patents

Abstract

720,264. Supply systems for space-discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., and MILLS, R. V. May 18, 1951 [May 18, 1950], No. 12477/50. Class 38 (4). The current flow through, and hence the light output from, an electric-discharge lamp 10 is varied by a variable impedance which is connected in a manner known per se to the secondary winding 15 of a series transformer whereby to vary the reflected impedance in a series circuit which comprises, connected to A.C. supply terminals 11, the lamp 10 and the primary winding 14 of the transformer, the stabilizing inductance for the lamp being either serially connected in the transformer primary or secondary winding circuits, or incorporated in the transformer. As shown, the impedance comprises a variable resistance 16, movement of the arm 17 of which varies the lamp brightness. With maximum resistance in circuit the resistance 16 may be disconnected to opencircuit the secondary winding, but to further decrease the light output an A.C. supply of the same frequency as that of the lamp supply may be applied across the series arrangement of a part BC of the resistance 16 and an additional fixed resistance 18 and is so connected as to cause an opposing voltage to be injected into the primary winding 14. Also as shown, the lamp is started by a thermal starter switch 13, but in a preferred arrangement, Fig. 2 (not shown), the lamp is provided with an earthed starting-strip and a filament-heating transformer. In this arrangement two parallelconnected lamp groups are connected to a common variable dimming impedance and the lamp in each group may be replaced by two lamps connected in series. In another arrangement the resistance 18 is replaced by an auto transformer winding which is supplied similarly to such resistance and the turns of which are selected by another arm which is connected to secondary winding 15. Specification 414,510 is referred to.