Metal Halide Lamp Guide

Metal Halide Lamps

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In contrast to incandescent lamps, which are thermal radiators pure and simple, metal halide lamps generate light from an arc, which burns between two electrodes.

Metal Halide - Product Catalogue

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Advantages of Metal Halide

The most important advantages over incandescent light are the three to four-fold increase in luminous efficacy (almost 100 Im/W), a daylight spectrum with a colour temperature between 4500K and 6500K, and a luminance value which is 20 times higher, bringing the lamps very close to the ideal of a point light source. In addition, the light from metal halide lamps has a colour-rendering index of between 80 and 95, which almost matches the maximum possible "Natural" rendering of non-luminous colours (100). For some applications it is also important that certain lamps, can be hot-restarted at any stage of cooling.

Some metal halide lamps are single ended with outer bulbs and are designed only for cold starting.

Operating Conditions
Metal Halide lamps are operated on an ac voltage. Unless noted to the contrary, lamps are suitable for 220V and 240V. This is supplied by chokes or high-reactance transformers or by electronic control gear. Electronic control gear operates with a constant output and ensures flicker-free light. Lamps will start and operate with a 10% reduction in rated supply voltage provided the correct control gear is used. However, in order to maximise lamp survival, lumen maintenance and colour uniformity, it is recommended that the supply voltage and ballast design voltage should be within + / - 3%.
Run-Up
When a metal halide lamp is switched on, current first flows through the starting gas of the arc tube. The heat generated vaporises the halide filling until operating conditions are achieved. This is known as the run-up period and can take several minutes before the lamp stabilises and produces the correct amount of light and colour. Run-up times are the time it takes for the lamp to reach 90% of normal light output.

In a cold state, metal halide lamps, like all discharge lamps, are excellent insulators and have to be made conductive with a high-voltage discharge (ignition). Whereas only a few kilovolts are needed to ignite a cold lamp, surge voltages ten times higher are required for hot restarting.
Used in
Film and television
Stage and theatre
Professional photography
Entertainment
Applications
Effect spotlights
Effects lighting
Slide projection
Overhead projection
Multimedia projection
Endoscopy
Boroscopy
Safety
Metal halide lamps emit UV radiation and operate at overpressure and must only be used in appropriate fully enclosed luminaries. Suitable filters should be used to ensure that UV radiation is reduced to an acceptable level.
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