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What is a Metal Halide Lamp? – Construction, Working, and Applications
A metal halide lamp, also called mercury halide lamp, is an electric lamp that produces light by an electric arc through a gaseous mixture vaporized mercury and metal halides. The metal halide lamp was invented by Dr. Reiling in 1960.
Construction of Metal Halide Lamp
The construction of a metal halide lamp is shown in the figure below −
A metal halide lamp consists of a metal base and a glass shield to protect the internal components of the lamp. Inside the glass shield, there is a series of lamps combined within a single arc tube with output characteristics of different mixtures of elements. The compact arc tube contains a mixture of argon, mercury and a variety of metal halides at high pressure.
Working of Metal Halide Lamp
When electric voltage is applied to the metal halide lamp, the argon gas in the lamp is ionized and facilitates striking of the arc across the two electrodes. The heat produced by the arc vaporizes the mercury and metal halides which produces light when the temperature and pressure increase.
The nature of the metal halides affects the nature of light produced by the lamp. Sometimes a phosphor coating is also provided on the inner side of the outer glass envelope to improve the spectrum and diffuse the light. To reach the full light output, metal halide lamps require around 3 to 5 minutes.
Metal halide lamps require electrical or electronic ballast to stabilize and regulate the arc current flow and to deliver the proper voltage to the arc.
Advantages of Metal Halide Lamps
The advantages of using metal halide lamps are listed below −
Metal halide lamps have high lamp efficiency around 60 to 115 lumens per watt.
Metal halide lamps have long lifespan around 10000 to 20000 operating hours.
Metal halide lamps do not require any starting gear.
Disadvantages of Metal Halide Lamps
Listed below are some of the disadvantages of using metal halide lamps −
These lamps are not environmental friendly due to the presence of mercury.
The cost of metal halide lamp is higher than incandescent lamp.
Metal halide lamps produce high heat when in operation.
Metal halide lamps require some starting time.
Applications of Metal Halide Lamp
Metal halide lamps are used in the following applications −
High bay interior lighting
Domestic and commercial lighting
Sports stadium lighting
Flood lighting, etc.
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