| 摘要 |
PROBLEM TO BE SOLVED: To provide excellent distribution characteristic or emission efficiency properly keeping the bulb wall loading by arranging an anode and a cathode opposite to each other within a bulb, sealing a rare gas, mercury and a halide metal, and forming the bulb so that the curvature radius in the cathode-side part is larger than that in the anode-side part. SOLUTION: In a metal halide lamp, a bulb 1 is formed so that the curvature radius in its cathode-side part 1d is larger than that in the anode-side part 1c. Since the anode-side part 1c of the bulb 1 has a relatively small curvature radius, the form can be made as close as possible to a circular form about the arc center of a lamp while properly keeping the bulb wall loading to provide a bulb form excellent in distribution characteristic. On the other hand, since the cathode-side part 1d of the bulb 1 has a relatively large curvature radius, the cathode 3-side root can be made difficult to cool by shortening the distance between the root of the cathode 3 and the bulbs to provide a bulb form excellent in emission efficiency.
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