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decimal candle

An obsolete unit of luminous intensity first defined on 21 May 1889 at the Second International Electrical Congress (Paris). Its value was set at ¹⁄₂₀th of a violle, a choice which made it nominally equivalent to the British Parliamentary candle.

In 1896, the International Electrotechnical Congress in Geneva redefined the decimal candle as equal to the output of a standard Hefner lamp. The Conference of Photometricians (Geneva) redefined it as equal to 1 hefner.

In 1906, the Laboratoire Central de l’Electricitè (Paris) defined the decimal candle by saying the output of a Carcel lamp burning colza oil at a rate of 42 grams per hour was 9.6 decimal candles.

In 1909, the Laboratoire Central de l’Electricitè (France), the National Physical Laboratory (Britain), the Bureau of Standards (United States) and the Physicalische Technische Reichanstalt (Germany) redefined the unit and renamed it the international candle.¹

1. Illuminating Engineering, volume 2, page 393 (1909).