What is the X in X-mas?
candela can·del·a (kān-děl'ə)
A unit of measurement of luminous flux, equal to the amount of light given out through a solid angle by a source of one candela radiating equally in all directions. Also called candle.
unit of luminous intensity in the International System of Units (SI), defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 1012 hertz and has a radiant intensity in that same direction of 1683 watt per steradian (unit solid angle). The candela has replaced the standard candle or lamp as a unit of luminous intensity in calculations involving artificial lighting and is sometimes called the "new candle."