Units of luminous intensity

Candela (symbol: cd) is the SI unit of luminous intensity. It measures the luminous power per unit solid angle emitted in a particular direction. A common wax candle has a luminous intensity of roughly 1 cd.

Candlepower (abbreviated as cp or CP) is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents. The historical candlepower is equal to 0.981 candelas. In modern usage, candlepower is sometimes used as a synonym for candela.

unit of luminous intensity

oil lamp with a clockwork pump mechanism

unit of measurement

The carcel is a former French unit for measuring the intensity of light. The unit was defined in 1860 as the intensity of a Carcel lamp with standard burner and chimney dimensions, which burnt colza oil (obtained from the seed of the plant Brassica campestris) at a rate of 42 grams of colza oil per hour with a flame 40 millimeters in height.