ARC TUBE TRANSPARENCY LOSS DUE TO STARTING OF HID LAMPS

A temporary loss of are tube wall transparency during starting is obse rved in metal halide lamps. This temporary transparency loss occurs wh en mercury is cleaned from the electrode surface by the starting disch arge. Mercury vapor then condenses on the wall as a thin film that is subsequently volatilized as the are tube warms to its steady-state con dition. Temporal changes in the are tube wall transparency of metal ha lide lamps have been measured. In addition, there is a permanent trans parency loss over the life of the lamp resulting from the deposition o f sputtered electrode material. These transparency changes of the are tube wall have been determined by laser transmittance measurements dur ing rated wattage, stabilized lamp operation. The are keeps the mercur y and most of the salts off the wall. The measurement utilizes lock-in detection techniques providing a signal insensitive to laser power fl uctuations and plasma radiation. The experimental technique is describ ed. Transparency variations over a 1000 hr burning period between a co ntinuously burned lamp and a lamp on a rapid starting cycle are presen ted.