GB955656A - Operation of electric discharge lamps - Google Patents

Abstract

955,656. Discharge lamps. A.E.I. LAMP & LIGHTING CO. Ltd. May 6, 1960 [May 19, 1959], No. 16993/59. Heading H1D. [Also in Division H2 ] A circuit arrangement for operating a sodium vapour and rare gas electric discharge lamp 1 having spaced thermionic electrodes 2 and an electrical heating element 4 around the envelope, comprises a transformer 3 having a primary winding connected to a source 5, 6 of A.C. supply and secondary windings connected to supply heating current to the electrodes 2, connections from the transformer 3 for supplying heating current to the element 4, and a separate source 7, 8 of A.C. supply, the frequency of which can be changed, for providing the operating current for the discharge, the separate A.C. source being connected between the electrodes 2 through an inductive reactance 9 so that the operating current can be varied by a change in the frequency of the separate A.C. source. The inductive reactance 9 is arranged to have substantially a minimum impedance at a predetermined frequency of the separate A.C. source, the frequency of the separate source being raised when it is required to diminish the intensity of the discharge current. The filling can be sodium with a vapour pressure of about 0.9 microns corresponding to a metal temperature of about 230‹ C. together with neon and/or argon and xenon. The sodium vapour discharge lamp described in Specification 955,655 is referred to. The separate source 7, 8 of A.C. supply can be a change-pole alternator for two operating frequencies or an alternator rotated through a variable speed motor for a continuous variation in frequency. Means can be provided for simultaneously switching on the supply to the heating element and to the electrodes when the frequency of the separate supply is altered from some value to a higher value. One lead wire of the supply 5, 6 can be common with one lead wire of the supply 7, 8 and a number of lamp arrangements can be connected in parallel by the lead wires and operated from a central location by a plurality of push buttons. The arrangement is such that lamp watts plus heater watts is constant. The supply 5, 6 can be taken from a tapped transformer and the supply 7, 8 from H.F. rotary converters or electronic valve oscillators and amplifiers when a number of light output levels is required.