The Carcel is a former French unit for measuring the intensity of light

Illuminance

In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...

. The unit was defined in 1860 as the intensity of a Carcel lamp with standard burner and chimney dimensions , which burnt colza oil

Colza oil

Colza oil is a nondrying oil obtained from the seeds of Brassica rapa, var. oleifera, a variety of the plant that produces turnips. Colza is extensively cultivated in France, Belgium, the United States, the Netherlands and Germany and Poland. In France, especially, the extraction of the oil is an...

(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.

In modern terminology one carcel equals about 9.74 candelas.