GB1506433A - High pressure sodium vapour lamps - Google Patents

Abstract

1506433 Metal vapour lamps GENERAL ELECTRIC CO 20 March 1975 [1 April 1974] 11614/75 Heading H1D In a high pressure Na vapour lamp charged with Na amalgam in excess and inert gas, e.g. Xe, with 10-40% W./W. Na, in an alumina discharge envelope of uniform bore 3À0-7À5mm. between the electrodes, over which space the loading is 14-24 W./cm<2> of external surface, to run at given wattage 50-300 W and voltage drop 20-180 V.r.m.s., the bore is selected within Œ 20% from Fig. 2, after which the cooling of the coolest part is adjusted for optimum efficacy lumens/W. Voltage gradient is a function of heat loss, the lumens/W. passing through a peak at same voltage drop (Fig. 1, not shown); to operate at a given volt drop the heat loss is adjusted for optimum lumens/W. while the inter-electrode gap is chosen for the required voltage drop. The voltage drop is preferably just below 50% of the r.m.s. alternating mains voltage, allowing a ballast reactor to be used. Control of heat loss is applied to the coolest part, the sealed-off metal, e.g. Nb, exhaust tube at the lower end of the lamp (Fig. 3, not shown) where excess amalgam collects: the exhaust tube may be altered in length, roughened or painted. The heat impedance of the metal connection to the exhausttube may be varied. The envelope lies in an outer evacuated glass envelope carrying a base.