A unit of illumination, being the amount of illumination of a unit area of spherical surface, due to a light of unit intensity placed at the center of the sphere.
- Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
- Physics The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions. See Table at measurement.
- Botany The cavity bounded by a plant cell wall.