candle

One of several obsolete units of luminous intensity. Originally actual, standardized candles were used, often made of spermaceti. Real candles, however, do not make very good physical standards; candles taken from the same package were reported to vary in light output by as much as 15%. The extent of this variation became significant as related measurements became more precise, and, whales becoming scarce, the candles were replaced by

various standardized lamps burning pure chemical compounds (see hefner), then by
blackbody radiators at the temperature of freezing platinum (see violle and candela),
and finally by
the redefined candela, the unit of luminous intensity in SI.

According to the current national standard in the United States¹, none of the candles, and including candlepower, may be used. The candela should be used instead.

Period	Unit	Equivalent in candela
1889-	Various National Candles
	Britain
	candle (English)	0.96 international candle
	Harcourt pentane lamp
	Germany
	Munich candle
	Vereinskerze	0.95 international candle
	Hefner	0.903 candela
	France
	Carcel unit	0.98 candela
1889	decimal candle	= 1/20 violle, about candela
1896	decimal candle	= 1 hefner, about 0.903 candela
1909	international candle
1946	new candle
1948	candela

Other candles included

candle (pentane) = 1.00 international candle

1. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.

See Section 3.3.3.