| 摘要 |
PROBLEM TO BE SOLVED: To provide a ceramic discharge lamp having less amount of water molecules taken in a bulb and expected lamp characteristics at low production cost. SOLUTION: A ceramic discharge lamp has a bulb 10 made of light transmissive polycrystal alumina, and a pair of electrodes 21 arranged so as to face each other within the bulb 10. The surface covering ratio of calcium on the surface of the bulb 10 is specified to 3% or less. The average crystal particle size of the light transmissive polycrystal alumina constituting the bulb 10 is preferable to be 20-40μm.
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