A lamp utilizing the microwave is described in Japanese Patent Application Laid-Open No. 07-182910. The lamp described in the Japanese application is configured to seal a gas in an envelope and irradiate the gas with the microwave to excite the gas, thereby inducing emission of light. The gas contains a fluorine base gas, the fluorine base gas etches the internal surface of the silica glass envelope, and Si impurities made by the etching adhere to the internal surface of the envelope. Then, the lamp described in the Japanese application has a cooling pipe penetrating the interior of the envelope and is arranged to attach the impurities made by the etching with the fluorine gas, to the cooling pipe.
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