Metal vapor discharge lamp including an inner burner having tapered ends

Claim 1

A metal vapor discharge lamp comprising: a light emitting tube of translucent ceramics having a straight tube section having a diameter of greater than 9 mm and a pair of tube end sections formed integrally with said tube, one at each end of said straight tube section thereby defining a first end and a second end such that each said tube end section has its diameter gradually decreased from a boundary with said straight tube section; a pair of sealing members made of ceramics which hermetically seal said ends of said decreased-diameter portions of said tube end sections; a pair of discharge electrodes each having an electrode rod and a radiator section formed on and around the electrode rod, said discharge electrodes formed one at each end of the light emitting tube such that each said discharge electrode is supported by the corresponding sealing member; at least one light emitting metal added within said light emitting tube; and a rare gas within the light emitting tube for starting the tube; wherein: said light emitting tube being formed such that a height H from the sealing member on said first end to the boundary of the straight tube section and the tube end section on said first end is greater than a height h 1 from the first end sealing member to a closest end of said radiator section of the discharge electrode on said first end, or H>h 1 , and that a minimum radius D/2 of the tube end section of the light emitting tube is greater than an outer radius d/2 of said radiator section of said discharge electrode with the difference E between these radii being 1.5 mm or less, or E=D/2-d/2≦1.5 mm.