Lithograph of painting depicting Carcel demonstrating the lamp he invented to his sons, by B. De Monvel. The Carcel lamp was invented in 1800 by the clockmaker Bertrand Guillaume Carcel ( 1750-1812) . It consists of a lamp lit with vegetable oil via a pump driven by a clockwork mechanism wound up by a key. The clockwork kept the delivery of oil steady and constant for almost ten hours. 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. This image has been color-enhanced.