Like the fluorescent tube light and the CFLs, Metal Halide Lamps are also discharge tubes in which an electric arc is discharged through a mixture of gases- generally a combination of mercury vapour, argon and halides like iodides or bromides of different metals. The main difference between a Metal Halide (MH) Lamp and a CFl is that the intensity of discharge in a MH Lamp is far higher and the arc length is far smaller so as to almost be considered a point. This allows manufacturers to design accurate optic trays, diffusers and lenses for a variety of applications.
ADVANTAGES OF METAL HALIDE IN GREEN BUILDINGS:
Colour rendering properties: Metal Halide lamps have excellent colour rendering properties, Ra – 85 to 96, and are comparable to Incandescent bulbs (Ra of 100) in this respect.
Efficiency: They are very efficient, producing from 60 to 115 lumens per watt depending on the type of Metal Halide.
Wattage range: They are available in a wide wattage range that starts at 20W and goes upto 2000W! This allows their use in every likely application segment.
Life: The lamp life is quite high in comparison to Incandescents at 9000 hours, but still much less than the 20,000 hours of Fluorescent Tube light and 50,000 hours of CFLs.
The advantages of Metal Halide lamps listed above make them an attractive option for applications in Interiors for retail, art etc. as well as for exterior illumination of buildings,monuments and landscapes, street lighting and floodlighting of large arenas and sports venues.
DISADVANTAGES OF METAL HALIDE IN GREEN BUILDINGS:
Initial cost: The initial cost of ownership is quite high: at Rs 1000 for a 35W lamp and Rs 1600 for the electronic ballast.
Control: They are not very easy to control and cannot be dimmed as of now.
Ignition time: They take a long time to ignite, almost 4 minutes and if switched off and on again, they take almost 6 minutes to re-ignite, as they have to first cool down.
Disposal: They contain mercury and issue of disposal should be addressed satisfactorily.
Due to the cost factor the Metal Halides still don’t find use in households. Since they take a long time to ignite, they are unsuitable in places where rapid re-strike is required like in a factory where power supply is constantly switched between normal and generator supply.
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