Patent ID: 7253563

Claim:
A metal halide lamp comprising: a translucent air tight vessel having a light emitting tube portion, in which a discharge space is formed, and sealed portions formed on both ends of the light emitting tube portion; a discharge medium enclosed inside the discharge space containing at least metal halide and rare gas; and a pair of electrodes sealed in the sealing portion one ends of which are arranged facing each other in the discharge space; wherein a shape of the light emitting tube portion forming the discharge space in a cross section perpendicular to a tube axis is nearly circular, wherein a shape of the bottom portion in the vertical cross section along the tube axis of the light emitting tube portion composed of a parallel portion, which is nearly parallel with the tube axis and has a lowest level at a portion between the pair of electrodes, and a tapered portion, which is gradually rising to the tube axis on both sides of the parallel portion, thereby accumulating the discharge medium on the bottom portion of the light emitting tube portion, wherein a wall thickness of the bottom portion of the light emitting tube is formed thinner than a wall thickness of a ceiling portion of the light emitting tube and wherein a wall thickness A 1 of the bottom portion of the light emitting tube portion and a wall thickness A 2 of a ceiling portion of the light emitting tube portion are designed to satisfy the relation expressed by the following formula; 0.2≦A1/A2≦0.8.