GB589037A - Improvements relating to electric lighting systems - Google Patents

Abstract

589,037. Kinematograph projectors. SIEMENS ELECTRIC LAMPS & SUPPLIES, Ltd., and ALDINGTON, J. N. June 15, 1945, No. 9785/44. [Class 97 (i)] [Also in Groups XXXV and XL] An electric discharge lamp L (see Group XL) for use in a kinematograph projector is metallically connected across a capacitance C2 charged from a direct current source through a resistance R3 to a peak voltage less than the fundamental breakdown voltage of the lamp ; rapidly recurrent impulses of high voltage (not less than 24 per second and preferably 50 or even 100 per second) are applied to the lamp, e.g. from a spark coil S whereby breakdown occurs at each impulse and the capacitance is discharged across the lamp producing a high current density discharge of short duration. The duration of current flow may be not more than one per cent of the duration of operation, the peak current during an impulse being not less than one hundred times that which the lamp could carry on steady load. The lamp may be cooled by water or air-blast particularly when near the condenser of the projector. In the arrangement shown one end. of the secondary of the coil S is wrapped round the tube L. Periodic excitation of the primary is effected bydischarge of a condenser C1 through the plate circuit of a gas valve TH the condenser being charged from a voltage source through a resistance R2 ; the rate of flashing may be controlled by the values of the resistance and the condenser or by controlling the application of bias to the grid of the valve, e.g. the intermittent feed of the projector may be arranged periodically to short-circuit a resistance across the terminals e, f. Alternatively control may be exercised photo-electrically from a track on the film. Specifications 569,267, 579,686 and 586,685, [all in Group XL], are referred to.