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Abstract
We have developed a new type of retrofit HPS lamp which achieves the improved color rendering properties, general C.R.I. 50–60 with higher luminous efficacy of 105–130 lm/W (220 W-660 W), and can be operated on the conventional mercury lamp ballast by a bimetallic starter unit in the outer bulb. High pressure xenon as a inert gas was effective to obtain the new lamp, lowering total thermal conductivity of the arc. New sealing glass mainly composed of Al2O3 and CaO which had superior stabilities to the high temperature sodium and newly designed electrodes which improved the voltage rise of the lamp during operation were useful to realize this lamp.