Ballasts are required to regulate electricity for use in gas discharge lamps. Most energy- efficient lights require a ballast. The UV radiation is produced by passing an electric arc through argon and mercury gases. Metal Halide lamps create light by passing an electric arc through a tube containing metallic salts, mercury vapour and argon gas. LED exit lights contain a series of small light emitting diodes like those found in many household clocks.
Photocells control light operation depending on surrounding light levels.
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