Electrode for miniature high pressure metal halide lamp

摘要

An electrode for a miniature high pressure metal halide lamp having a volume not exceeding 1 cc and a discharge current not exceeding 1 ampere comprises a slender tungsten shank with a few secondary turns of mandrel-less coiled-coil overwind thereon and preferably a balled distal end. The shank diameter is chosen in the range of 5 to 15 mils and above the size where melt-back starts at the intended lamp current, and the overwind is made of primary wire not exceeding 3 mils originally wound on a primary mandrel of 3 to 7 mils subsequently removed. This assures a rapid glow-to-arc transition which provides good maintenance and also reduces ballast requirements.