GB444950A - Improvements in and relating to electric discharge lamps - Google Patents

Abstract

444,950. Discharge lamps. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. Jan. 30, 1936, No. 2848. Convention date, Jan. 30, 1935. [Class 39 (i)] A lighting unit consists of a low-pressure lamp 11 having a falling starting-voltage characteristic, a high pressure lamp 25 having a rising starting voltage characteristic and an incandescible filament 13, all enclosed in an outer envelope 10 and all in series; the envelope 10 may be evacuated or gas filled and the filament is in two sections. The lamp 11 has a filling of sodium at 1 to 2 microns, and some argon at 1-15 mm. pressure ; the lamp 25 has a filling of mercury and argon. The lamps and filament give a white light. The electrodes in the sodium lamp consist of nickel cylinders 17 on insulating plugs 18 ; they have internal heater coils 23 and are internally coated with barium oxide. A connection 22 is made from each lead-in 20 to the exterior of the cylinder. The electrodes 26 of the high pressure lamp may consist of pressed and sintered blocks or coils of tungsten or nickel impregnated with barium oxide. The internal leads of the unit are channel shaped bars 31, 33, which are connected to metal contacts 35. At starting a discharge takes place first across the high pressure lamp and after that across the low pressure lamp, the subsequent rise in voltage in the first lamp compensating the fall in the other and thereby preventing excessive change in the voltage drop across the filament at starting and during normal running. In a modification, a U-shaped sodimn-filled lamp is used with cold electrodes, while in another construction two low pressure lamps are used with one high pressure lamp all enclosed with the filament in an outer envelope, all the lamps and filament being in series.