Candlepower
| Candlepower | |
|---|---|
 The candlepower was based on the light emitted from a candle | |
| General information | |
| Unit system | international standard (obsolete) |
| Unit of | Luminous intensity |
| Symbol | cp |
| Conversions | |
| 1 cp in ... | ... is equal to ... |
| SI units | 1 candela (modern definition) |
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
[edit]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 1⁄6 pound (76 grams) and burns at a rate of 120 grains per hour (7.8 grams per hour). Spermaceti is a material from the heads of sperm whales, and was once used to make high-quality candles.
Calibration of lamps
[edit]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
[edit]Notes and references
[edit]Further reading
[edit]- Rowlett, Russ (2001-07-13). "How Many? A Dictionary of Units of Measurement". University of North Carolina at Chapel Hill. Retrieved 2007-07-10.
- 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.
- Coaton, J. R. (February 2002). "The genesis of incandescent lamp - manufacture". Engineering Science and Education Journal. 11. IEEE: 21. doi:10.1049/esej:20020103 (inactive 11 July 2025). Archived from the original on September 9, 2017. Retrieved 2007-07-10.
Measurement of the candlepower of lamps
{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link) - Cottington, Ian E. (February 1986). "Platinum and the Standard of Light - A Selective Review Of Proposals Which Led To An International Unit Of Luminous Intensity" (PDF). Platinum Metals Review. pp. 30, (2). Archived from the original (PDF) on 2013-01-31. Retrieved 2007-07-10.
Metropolitan Gas Act of 1860