The Candela:

The candela, represented by the lowercase non-italicized pair of English letters cd, is the standard unit of luminous intensity. It is equal to 1/683 of a watt of radiant energy released at a frequency of 5.4 x10¹⁴ hertz (cycles per second) in a solid angle of one steradian. This is a sentence full of arcane terms! Though, there is a simpler, albeit crude, definition: 1 cd is approximately the amount of light emitted by an ordinary candle.

The other definition, more specific than the candle orientation, does not rely on the use of derived units, a practice to which traditionalist legitimately can object. According to this definition, 1 cd symbolizes the radiation from a surface area of 1.667 x 10^-6 square meter of an absolutely radiating object known as blackbody at the solidification temperature of pure platinum.