Compact Fluorescent Lamps (CFLs) are energy-saving light bulbs, which last
longer and use far less energy than traditional (or incandescent) light bulbs
for the same level of light intensity.
Source: GreenFacts
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Compact fluorescent lamps (CFLs) can replace incandescent lamps that are
roughly 3–4 times their wattage, saving up to 75% of the initial lighting
energy. They are made of a glass tube filled with a low pressure mixture of
gases, specifically mercury and noble gases. The tube is coated on the inside
with a fluorescent material, usually a compound containing phosphorous. When the
current is switched on, the starting mechanism produces electrons that excite
the gases inside the tube which then release ultraviolet radiation. This in turn
excites the coating on the inside of the tube, which emits visible light through
the surface of the lamp.
