The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1⁄683 watt per steradian.
A common candle emits light with a luminous intensity of roughly one candela. The candela is the standard unit of luminous intensity in the International System of Units ( SI ). It is the power emitted by a light source in a particular direction, weighted by the luminosity function or a standardized model of the sensitivity of the human eye to different wavelengths.
The candela is also called candle such as in foot-candle or in candlepower.
== References ==
http://www.electro-optical.com/eoi_page.asp?h=What%20Is%20Visible%20Radiation http://physics.nist.gov/cuu/Units/candela.html http://en.wikipedia.org/wiki/Candela
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