| 摘要 |
PROBLEM TO BE SOLVED: To stop an outer tube discharge safely and rapidly when a discharge occurs in the outer tube. SOLUTION: A metal halide lamp La comprises a luminous tube 1 in which mercury, rare gas, and metal halide are sealed, a pair of electrodes 2 which are arranged in the luminous tube 1 so that they face each other, and an outer tube 3 which surrounds the luminous tube 1 and has a vacuum inner space. A current fuse 16 is attached at an internal portion of a base 10. The metal halide lamp comprises a heat response type switch SW which is formed of a bimetal that has one end connected to a conductor part 15a and the other end spaced away from a conductor part 15b. The heat response type switch SW operates owing to heat of a discharge when the discharge occurs in the outer tube, then the heat response type switch SW generates an electric short- circuit between the conductor parts 15a and 15b so as to stop the discharge occurred in the outer tube. At the same time, the current fuse 16 which is provided at the base 10 is melted and cut, and electric power is stopped to be supplied from a lighting circuit 20 to the metal halide lamp La. |
