Abstract
The arc tube temperature of a high-pressure sodium lamp is determined from the luminance in the sodium D line and compared with infrared temperature measurements. Good agreement is found after correction for the inside to outside wall temperature difference. The luminance method is used to determine the arc tube temperature in an experiment in which nine lamps are burned for 524 h, after which the normal transmissions of the glass outer jackets are measured. Greater than expected darkening of the outer jackets from standard unground polycrystalline alumina arc tubes is observed when compared with the theory for alumina sublimation from smooth-ground polycrystalline alumina. Little darkening was observed from smooth sapphire (single-crystal alumina) arc tubes. It is suggested that surface irregularities may enhance alumina sublimation from the standard unground alumina.
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