Metal Halide lighting is a type of High Intensity Discharge (HID) lighting. Other types of HID are Mercury Vapour, High Pressure Sodium and Low Pressure Sodium. All HID lamps work on the same principle, that of causing an arc across a gas or vapour and using the gas or vapour as a conductor, the same way incandescent lamps use a tungsten filament as its conductor.Prior to the Metal Halide Lighting system most HID type lighting was used outdoors. This is due to ballast noise and the ill effect this type of light has on colour. The Metal Halide has reduced the excessive noise and has improved on the colour effect, especially at the red end of the spectrum. With these improvements, Metal Halide is being used more and more for indoor applications including gymnasiums and in low ceiling warehouses. However, Metal Halide is not without its problems, specifically extreme heat and the possible emission of ultraviolet rays. These two faults have proven to be a Health and Safety concern for workers. When fully lit, the Metal Halide lamp will reach a temperature of 2000 degrees Fahrenheit and operates at a vapour pressure between 70 and 90 pounds per square inch. Normal use of Metal Halide lighting requires that they are very rarely, if ever shut off. The constant heat takes its toll on the glass of the inner and outer cone, causing them to deteriorate and possibly break.
When the lamps break, extremely hot fragments will fall to the ground, possibly landing on workers or combustible materials. Millions of dollars in property have been lost because of the fires caused by Metal Halide lighting, but more importantly there have been serious burns/injuries to workers. (Saskatchewan, 2004)
Another danger of these lamps is the possibility of the leakage of Ultraviolet Rays. Again, after long use and the deterioration of the inner cone, the lamp may develop cracks. Ultraviolet rays can leak through these cracks. For workers, the danger is that the rays can cause burns (similar to a sunburn) or skin irritation, when exposed over a period of time. Another area of concern are the workers' eyes. The contact of the ultraviolet rays with the eyes over a period of time could be compared to that of a welding flash, however, is not as intense but equally damaging and painful. The dangers of this method of lighting can be reduced by regular replacement and maintenance. One method of maintenance is to shut the lamps down once a week for fifteen minutes. This will allow the lamp to cool. If it is damaged or deteriorated, the lamp is less likely to re-light.
