Metal halide lamps produce a bright white light and are highly efficient
members of the HID family. They were an outgrowth of the mercury lamp with an
improvement made in their color rendering characteristic and energy efficiency. The
efficiency of metal halide lamps is from 1.5 to 2 times that of mercury vapor
lamps. Almost all varieties of available "white light" metal halide lamps
produce color rendering which is equal or superior to presently available mercury
vapor lamps.
The metal halide lamp is very similar in construction to the mercury vapor lamp. The major difference is that the metal halide lamp contains various metal halide additives in addition to mercury vapor. Metal halide lamps are commonly used in stadiums, warehouses and any industrial setting where distinguishing colors is important. Low wattage lamps are available and have become popular in department stores, grocery stores, and many other applications where light quality is important
Metal halide lamp sizes range from 175 to 1,500 watts. Ballasts designed specifically for metal halide lamps must be used.
Strengths:
Designed for general lighting applications.
Relatively long lamp life.
Interchangeable with mercury lamps in many applications.
Concentrated source is easily controlled by special fixtures.
Good color rendering characteristic.
Light output is a bright crisp white light.
Twice as efficient as mercury lamps and 6 times as efficient as incandescent.
Weaknesses:
Short life compared to other HID lamps (6,000 to 20,000 hours depending on
size and manufacturer).
Different lamps have to be used for base-up versus base down burning
configurations.
Horizontal operation may severely reduce lamp life.
Require a ballast.
Some lamp types require 2 to 5 minutes to warm-up before giving full light
output and 10 minutes to cool-down. Others have instant restart capability.
Color may vary from lamp to lamp (color shift)
Many wattages require operation in enclosed fixtures due to the risk of lamp
breakage upon failure.
