Low pressure metal or metal halide lamps for photocopying applications

Claim 1

In apparatus in which a radiation pattern is projected from an information bearing member illuminated by a visible light source onto a charged photoconductive insulating member to imagewise discharge said photoconductive member to form a latent electrostatic charge pattern corresponding to said information bearing member, an improved low pressure metal vapor lamp having a short warmup time which when ignited emits visible light having a radiation intensity level sufficient to expose said photoconductive member and which when operated in a standby mode has a standby temperature which permits such short warmup time and provides increased lamp efficiency, said improved lamp comprising: an outer envelope having a substantially transparent annular cross section and being coated with a diffusely reflecting material about a portion of the periphery thereof, said diffusely reflecting material being reflective of visible illumination, said diffusely reflecting material extending in a logitudinal direction to form a longitudinally extending aperture of a predetermined geometry along said envelope for directing said visible illumination onto said information bearing member. an inner envelope within said outer envelope in spaced, substantially coaxial relationship therewith and containing a combinational quantity of low pressure sodium vapor and gas fill mixture, said inner envelope including electrode means adapted when energized for initiating an ionization discharge of said gas within said inner envelope, resistance heating means operatively associated with said inner envelope and adapted when energized to heat said inner envelope and thereby heat said sodium vapor and gas fill mixture therewithin to said predetermined standby temperature, said resistance heating means comprising an oxidation resistant material having an increasing resistivity relative to temperature, heating control means operatively connected to said resistance heating means through said outer envelope for selectively energizing said heating means and maintaining said inner envelope at said predetermined standby temperature, and lamp control means operatively connected to said inner envelope electrode means through said outer envelope for selectively energizing said inner envelope electrode means and initiating said ionization discharge of said gas within said envelope and illuminating said information bearing member.