High-efficiency discharge lamp which incorporates a small molar excess of alkali metal halide as compared to scandium halide

Claim 1

An arc-discharge device comprising a sealed elongated light-transmitting arc tube envelope which encloses a predetermined volume, electrical lead-in conductors sealed through said envelope and electrically connected to electrodes which are operatively positioned proximate the ends of said envelope and spaced apart a predetermined distance within said envelope, and a discharge-sustaining filling enclosed by said envelope and having the following as essential constituents: mercury in predetermined amount as required to provide a mercury-vapor pressure in said envelope of from one to ten atmospheres as calculated on the basis of mercury being fully vaporized as the sole discharge-sustaining constituent with an average mercury vapor temperature of 2000°K; a small charge of inert ionizable starting gas; alkali metal halide of sodium iodide or sodium bromide or lithium iodide or lithium bromide or any mixtures thereof; scandium halide of scandium iodide or scandium bromide or any mixtures thereof, wherein the molar ratio of said alkali metal halide to said scandium halide is from about 1.7:1 to about 5:1; and said alkali metal halide plus said scandium halide is present in said arc tube envelope in total amount of at least about 0.1 mg/mm of spacing between said electrodes.