lumen

noun

1. a unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions

   noun.quantity

   Synonyms lm

   Source: WordNet 3.0

2. a cavity or passage in a tubular organ

   noun.body

   Examples

   The lumen of the intestine.

   Source: WordNet 3.0

3. 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.

   noun

   Source: webster1913