Low pressure sodium discharge lamp for xerography - has cylindrical envelope with slit for directed light emission and is radiation cooled

摘要

The gas discharge lamp uses sodium vapour under low pressure, esp. for monochromatic illumination for achieving good contrast in xerography, running at a fairly high power level and with the light emitted in a controlled direction. The lamp consists of a cylindrical discharge tube (4) housed concentrically in an outer cylinder (6). The space between them is filled with a gaseous heat conducting medium to conduct heat away from the discharge to the outer air. To control the direction of emission of light, the outer envelope is covered with a diffusely reflecting layer (18) and a longitudinal slit along which the light issues.