Ceramic envelope device for high-pressure discharge lamp

A ceramic envelope device for a high-pressure metal vapor discharge lamp comprising:

• a translucent ceramic tube having a first end and a second end and an inner peripheral surface and an outer peripheral surface;
• a first electrically conducting cermet end cap having an inner surface and an outer surface, said first electrically conducting cermet end cap closing said first end of the ceramic tube;
• a second electrically conducting cermet end cap having an inner surface and an outer surface, said second electrically conducting cermet end cap closing said second end of the ceramic tube;
• a first discharge electrode having an inner end and an outer end and an outer peripheral surface, said outer end of the first discharge electrode being inserted into said inner surface of said first end cap such that said inner end of the first discharge electrode protrudes from the inner surface of the first end cap longitudinally into the ceramic tube;
• a second discharge electrode having an inner end and an outer end and an outer surface, said outer end of the second discharge electrode being inserted into said inner surface of said second end cap such that said inner end of the second discharge electrode protrudes from the inner surface of the second end cap longitudinally into the ceramic tube;
• a pair of electrically insulating members, each electrically insulating member having an outer surface which contacts said inner surface of the first and second electrically conducting end caps, respectively, at least one of said pair of electrically insulating members having an inner protruding portion which protrudes longitudinally into the ceramic tube, said inner protruding portion creating a radial gap between said inner peripheral surface of the ceramic tube and said protruding portion and also creating a predetermined radial gap between said protruding portion and a corresponding outer surface of at least one of said first and second discharge electrodes, wherein a corresponding inner surface of at least one of said first and second end caps does not extend longitudinally into said ceramic tube beyond said outer surface of the corresponding electrically insulating member.