DIMMING OF METAL HALIDE LAMPS

Metal halide dimming systems have been available commercially for seve ral years. Recently, interest has increased in dimming applications, e specially because significant energy savings can result. This paper el aborates on recently reported metal halide lamp performance on dimming systems. The paper also discusses the photometric properties of 400-W metal halide lamps at and below rated wattage. These properties inclu de luminous flux, correlated color temperature, and color rendering. L amp color shift upon low-power dimming can be overcome when coated met al halide lamps are utilized; data are presented to support this claim . Additionally, the time for metal halide lamps to respond to a 50 per cent change in power on bi-level dimming systems is presented. Lamps r each 90 percent of their stable color and luminous flux within only, 6 0 s of the power switch. Finally, life test results for lamps on bi-le vel cycle tests show that the lumen maintenance deviates from the cont rols when lamps are operated at half power more than 5 hr at a time; t est lamps cycled more frequently between high and low power show lumen maintenance the same as the control lamps.