Patent GB-908672-A (GB)
Title: Improvements in or relating to operating circuits for sodium vapour electric discharge lamps
Inventor: RIGDEN SYDNEY ALFRED RICHARD
IPC: H01J61/74
Filed: 1959-03-02
Abstract: 908,672. Supply systems for space discharge apparatus. GENERAL ELECTRIC CO. Ltd. March 1, 1960 [March 2, 1959], No. 7155/59. Class 38 (4). [Also in Group XL (a)] A discharge lamp operating circuit includes at least one straight or U-shaped sodium vapourrare gas low-pressure discharge tube 1 surrounded by a single- or double-walled jacket 2 and having in the space between the jacket and the tube at least one electrical resistance heating element 7 of " Nichrome " (Registered Trade Mark) extending along or partly along the tube, the input terminals 11 to the electrodes 4 being connected to a discharge current supply-means incorporating a switch S1 and the input terminals 12 to the heating element 7 being connected to a heating current supply means incorporating a switch S2, the arrangement being such that the discharge current can be adjusted either to a main value or to at least one smaller value and the heating current can be adjusted to a minimum value, preferably zero, when the discharge current is adjusted to the main value or to a higher value when the discharge current is adjusted to a smaller value. The filling of the discharge tube can be neon with 0.75% argon at a total pressure of 10 mms. together with about 1 gr. of sodium producing an operating pressure of less than 1 mm., preferably 0.01 mm. The discharge tube can be provided on each of its limbs with a sleeve of transparent heat-insulating material as described in Specification 801,482. The tube 1 and resistance elements 7 are supported by heat-insulating discs 35, 36. The switch S1 acts to connect ballast impedances Z 2  . . . Z n  of different values in series with the discharge current supply means and the switch S2 acts to connect impedances R 2  . . . T n  in series with the heating current supply means. The discharge current supply means can incorporate a secondary winding 15 of a transformer, and the heating current supply means a secondary winding 20. The transformer can be a strayfield transformer which provides automatically the lamp ballast required in the discharge current supply means. In a modification the switch S 2  acts to connect the heating current supply means to different tappings on the secondary winding of an associated transformer. The switches S1 and S2 can be linked so as automatically to adjust the discharge and heating currents to the desired values. In another arrangement in which the discharge current supply means incorporates a transformer there is included a pair of grid-controlled gas-filled valves connected in reverse parallel in the secondary circuit of the transformer so as to be in series with the lamp, the arrangement including means for applying a positive voltage pulse to the grid of each valve with respect to the cathode during the half-cycle in which its anode voltage is positive for initiating the discharge through the valve, and the discharge current control means can be arranged to vary the phase of each grid voltage pulse applied to each valve for varying the period of conduction of the valve and hence the value of the lamp discharge current. The heating current supply means then includes a control switch linked to the said control means and arranged to connect an impedance, or one of a number of different impedances, in series with the heating element. A lighting installation can include a plurality of lamp-operating circuits and can incorporate a master control circuit arranged to operate, by relays, the discharge current control means and the heating current control means in some or all of the lamp-operating circuits for enabling the lamps of those circuits to be dimmed simultaneously.