The candela (cd) is the SI unit of luminous intensity, which is a measure of power emitted from a light source. The definition for a candela is:[1]

The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Candela is Latin for the word 'candle', and a typical candle's luminous intensity is actually about equal to one candela.[2]

Visit Dr. Rowlett's unit dictionary to learn more about the candela, and learn more about luminous intensity here.


  1. NIST. Base unit definitions: Candela [Online] Available:
  2. SI Units Explained. Luminous Intensity [Online] Available: