DIMMING OF METAL HALIDE LAMPS

Metal halide dimming systems have been available commercially for several years. Recently, interest has increased in dimming applications, especially because significant energy savings can result. This paper elaborates 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 include luminous flux, correlated color temperature, and color rendering. Lamp color shift upon low-power dimming can be overcome when coated metal halide lamps are utilized; data are presented to support this claim. Additionally, the time for metal halide lamps to respond to a 50 percent change in power on bi-level dimming systems is presented. Lamps reach 90 percent of their stable color and luminous flux within only, 60 s of the power switch. Finally, life test results for lamps on bi-level cycle tests show that the lumen maintenance deviates from the controls when lamps are operated at half power more than 5 hr at a time; test lamps cycled more frequently between high and low power show lumen maintenance the same as the control lamps.