Ceramic metal halide lamps are high intensity discharge (HID)
lamps. HID lamps operate on the principle that an arc struck between
two electrodes produces light. Ceramic Metal Halide lamps utilize
a ceramic arc tube to contain the arc.
The ceramic tube can withstand higher temperatures and pressures
than a conventional glass arc tube. Thus, the lamp has slightly
higher efficacy and better color stability. The electrodes deteriorate
over time, which is a major cause of lamp failure.
Suitable Applications Include:
The best application for Ceramic Metal Halide is for directional
display lighting (i.e., track lighting) of retail displays. Other
good applications are lobbies, atriums, or foyers in commercial
or high-end residential areas.
Museums and art galleries are great applications as well. Anywhere
a high quality, directional light is needed, Ceramic Metal Halide
is the best choice.
The light source consists of a ballast, igniter, and bulb. The
ballast provides the start-up voltage, then backs off and delivers
a constant operating voltage and current. The igniter strikes
the arc. The bulb houses the arc tube. Bulbs come in various shapes,
including a reflector (PAR lamp).
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.
