MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Until the mid 19th century candles were the primary source of light. A candle is a cylinder of wax or animal fat, with a fibre wick running through its centre. Lighting the wick starts a physical/chemical process that results in the emission of light, heat, water vapour and carbon dioxide. At the base of the flame, in the oxygen rich blue zone, heated wax is liquidized and then vaporizes the hydrocarbons into molecules of hydrogen and carbon at around 1,400 degrees Celsius. The blue color is due to chemiluminescence. The dark orange region has relatively little oxygen. This is where carbon particles start to form. As they rise up they continue to heat until they ignite to incandescence and emit a spectrum of visible light, but much redder than daylight, about 1000 Kelvins. There is also an outer zone around the flame where complete combustion of wax takes place. It is light blue in color and not normally visible.
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