Analysis of the Characteristics of Inductively Coupled Electrodeless Metal Halide Lamps

Abstract

Dimming of conventional metal halide lamps readily causes changes in the lamp's color, decreases its efficacy, and reduces its lifetime. Employing inductively coupled electrodeless discharge in mercury-free metal halide lamps led to less color change and greater efficacy in dimming. The correlated color temperature of optimally designed lamps, containing a dose of ScI₃-NaI-SnI₂ and Xenon gas in the arc tube, was changed by only 300K at the 30% dimming ratio. The general color rendering index (R_a) did not shift greatly and the lamp's efficacy could be kept at 89% of the rated wattage efficacy at 75% of the rated wattage (1/4 greater than the conventional result). It was possible to correct the color characteristics during dimming by adding new metal halides to the ScI₃-NaI-SnI₂ lamp, keeping improved dimming characteristics. It was possible to correct color deviation and R_a by adding suitable amounts of DyI₃ or InI, though the lamp efficacy decreased by about 10% at the rated wattage.
This has proved that the dimming performance of metal halide lamps can be improved by employing inductively coupled electrodeless discharge in optimally designed mercury-free metal halide lamps.