Mercury-vapor lamp

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Mercury-vapor lamps producing a blue light

A mercury-vapor lamp is a special lamp. It makes light by a spark in a tube that contains mercury. The spark makes the mercury atoms release ultraviolet light. The ultraviolet light shines on phosphors which make white light from it. The EU wants to ban them because they contain large amounts of mercury and are not efficient like fluorescent bulbs. They last much longer though. They are the bluish streetlights. Depending on the quality of the bulb, age of the bulb, phosphor used, and other chemicals added to the mercury, the color of the light can vary from blue-white to green-white, to almost pure white. The metal halide lamp is an improved version of the mercury vapor lamp that contains a metal halide (usually sodium iodide) in addition to the mercury. The metal halide produces orange light, which combines with the blue-white light from the mercury to produce a very pure white light.

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