Ceramic metal halide lamp

A ceramic metal halide lamp having an arc tube, comprising an arc chamber where a metal halide, mercury, and a starting gas are sealed, and a pair of capillaries each having an electrode assembly inserted therethrough disposed on both ends of the arc chamber, the arc tube and the arc chamber being formed of translucent ceramics, wherein

• the capillary is formed continuously to each end of the arc chamber foamed substantially in an ellipsoidal shape in the direction of the longitudinal axis by way of a transitional curved area with no angled corner,
• the inner dimension of the arc chamber is designed as:
• 1.8≦L/D≦2.2
• where
• L is an effective length and
• D is an effective inner diameter, and
• the arc chamber is formed to a size that the lowest temperature in an arc chamber is 800° C. or higher and the highest temperature in the arc chamber is 1200° C. or lower during lighting, and
• at least thulium iodide, thallium iodide, sodium iodide, and calcium iodide are sealed as the metal halides, and sodium iodide and calcium iodide are sealed by a molar ratio of 40 to 80% and less than 30%, respectively, based on the entire metal halide.