High pressure metal halide lamp with electron collector

Claim 1

A high pressure metal halide discharge lamp for base-down operation comprising: a tubular fused silica arc tube having main arc-supporting electrodes sealed into opposite ends plus an auxiliary starting electrode in the upper end and a thermal switch mounted thereon for short-circuiting the starting electrode to the upper and main electrode at normal operating temperature, said arc tube containing an ionizable fill including mercury and sodium halide; a generally bulbous vitreous outer envelope surrounding said arc tube, domed at the upper end and having a base with terminals at the lower end, said outer envelope having a pair of stiff inleads extending thereinto and connected to said base terminals; a divided mount comprising a base end support frame fastened to one of said inleads and attached to the lower end of said arc tube and electrically connected to the lower end main electrode, and a dome end support frame attached to the upper end of said arc tube and engaging the dome end of said outer envelope, said divided mount providing substantially the entire physical support of said arc tube; a fine resilient lead wire extending from said other inlead and curving along the bulbous envelope wall to the main electrode at the dome end of said arc tube; and a collector wire extending alongside and close to said lead wire for collecting photoelectrons from said lead wire that would otherwise drift to the arc tube, said collector wire being connected to said one inlead at one end and extending to a current limiting resistor attached to said starting electrode at the other.