Abstract
We investigated the factors affecting the lumen maintenance of ceramic metal halide lamps using polycrystalline alumina arc tubes with NaI-T1I-DyI3 and NaI-DyI3. As a result, we found that the following phenomena of the arc tubes were the deteriorating factors.(1) Wall blackening due to deposition of residual carbon within the arc tube.(2) Deteriorating translucency originating from a formation of a 3Dy203-5Al203 garnet, thermal etching of alumina, and abnormal growth of alumina grains.To prevent the above phenomena, the amount of residual carbon on the tungsten electrodes should be reduced to less than 10ppm and the wall temperature of burning arc tubes should be kept between 950° and 1050°.
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