Patent ID: 7423380

Claim:
A metal halide lamp capable of being dimmed comprising: an arc tube that includes an envelope made of a translucent ceramic, a pair of electrodes, and metal halides, the metal halides including rare earth metal halide, sodium halide, and magnesium halide, the rare earth metal halide being at least one of dysprosium halide, thulium halide, holmium halide, cerium halide, and praseodymium halide, and the magnesium halide being at least one of magnesium iodide and magnesium bromide, wherein when a maximum lamp power P (W) is in a range of 70 W to 250 W, the following relations are satisfied: 0.0345 A+ 0.0028 B< 0.0015 P+ 0.0475, A≧= 0.021 P+ 0.313, and B≧= 10.0, where A (mg) represents a total content of the metal halides excluding mercury halide if any, and B (mol%) represents a content ratio of the magnesium halide to the metal halides excluding mercury halide if any.