| 摘要 |
PROBLEM TO BE SOLVED: To prolong the lifetime of a high-pressure sodium lamp. SOLUTION: This high-pressure sodium lamp is equipped with two light emission tubes 100a which are accommodated in respective inner tubes 200. Even if a leak is generated at any light emission tube 100a to cause generation of gas, it remains inside the inner tube 200, and there is no risk of leaking to the outer tube 300. In this case, lighting is continued with the other light emission tube 100, and a long-life, high-pressure sodium lamp can be established.
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