(a) a former unit of luminous intensity, defined as the intensity of the flame of a spermaceti candle of specified properties (see quot. 1937)…

A standard spermaceti candle formerly used as a unit of illuminating power: hence candle power; frequently called international candle. Also, with…

(a) see sense 1d; (b) the illuminating power of an electric lamp, etc., reckoned in terms of the light of a standard candle.