Candlepower (abbreviated as cp or CP) is the unit of luminous intensity in the United States customary systems of measurement. It is currently defined as being equal to 0.981 candela.
History The term candlepower was originally defined in the United Kingdom, by the Metropolitan Gas Act 1860, as the light produced by a pure spermaceti candle that weighs and burns at a rate of . Spermaceti is a material from the heads of sperm whales, and was once used to make high-quality candles.
Calibration of lamps To measure the candlepower of a lamp, a person judged by eye the relative brightness of adjacent surfaces—one illuminated only by a standard lamp (or candle) and the other only by the lamp under test. They adjusted the distance of one of the lamps until the two surfaces appeared to be of equal brightness. Then they calculated the candlepower of the lamp under test from the two distances and the inverse square law.
See also Candela Lumen (unit)
Notes and references
Further reading
International candle at Sizes.com Last revised: 27 June 2007. Accessed July 2007 Candle History - Candlepower 2003 Bob Sherman at Craftcave. Accessed July 2007. Brief History Of Lighting 2004 by The Wolfstone Group. Accessed July 2007. A History of Light and Lighting by Bill Williams Edition: 2.3 - (2005) Accessed July 2007.