Ceramic envelope device for high-pressure discharge lamp

摘要

A ceramic envelope device for a high-pressure metal-vapor discharge lamp, including a translucent ceramic tube, a pair of electrically conducting end caps closing opposite ends of the ceramic tube, and a pair of opposed discharge electrodes each of which is supported at its one end by the corresponding end cap such that the other end of the electrode protrudes from the inner surface of the corresponding end cap in a longitudinally inward direction of the ceramic tube. Each of the end caps is covered at its inner surface with an electrical insulator. The electrical insulator has a protruding portion surrounding a part of the corresponding electrode which protrudes from a radially central portion of the inner surface of the corresponding end cap. The surrounded part of the corresponding electrode is radially spaced from the protruding portion (the electrical insulator).