Metal Halide

Metal Halide

Higher-wattage, pulse-start metal halide lamps support and drive the trend toward white light and, along with ceramic metal halide lamps, are expected to replace incandescent and halogen sources.

Standard metal halide lamps in the 175-1000-W range that make up 70% of existing applications are expected to be replaced by either pulse start lamps or with the expanding family of ceramic metal halide (CMH) lamps.

Low-wattage metal-halide lamps and all high-pressure sodium (HPS) never used starting probes. Instead, they use a proven pulse starter to start the lamps. This starting method is not new--what is new is its use in higher-wattage metal halide lamps.

Standard (probe-start) metal halide lamps use a bi-metal switch inside the lamp to disconnect the starting electrode once the HID lamp is warmed up, which is eliminated in the pulse-start models. The best pulse-start lamp performance results are from a new family of lamps based on formed body arc tubes.

Formed body arc tubes feature higher fill pressures and more uniform geometry than pinched arc seal tubes. Temperature control is improved, which reduces lamp-to-lamp color shift. Design changes result in up to 80% higher lumen maintenance, up to 110 lm/W efficacy, 50% faster warm up and restrike, longer life, and more consistent lamp-to-lamp color.

Ceramic arc tube metal halide lamps, commonly designated CMH or CDM, usually refer to their constant color in their brands. CMH lamps were introduced to eliminate the problem of color shift of standard lamps and use PCA arc tubes--the same material used in HPS lamps. The PCA material reduces the sodium loss that causes color shift.

CMH lamps are commonly available in wattages below 150 W, but 250- and 400-W models are now available. CMH lamps have average rated life of 6000-20,000 hours and their lumen maintenance values fall in the 0.70-0.80 range. Warm (3000 K) or cool (4000 K) color temperatures and improved color rendering (CRI 85 and above) are available.

CMH lamps perform best on electronic ballasts. The advantages of the combination of CMH and electronic ballasts include 10-20% greater light output (which also results in a corresponding higher efficacy) and limited color shift.