||Lu"men (?), n.; pl. L. Lumina (#), E. Lumens (#). [L., light, an opening for light.] 1. (Photom.) (a) 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. (b) A unit of light flux, being the flux through one square meter of surface the illumination of which is uniform and of unit brightness.

2. (Biol.) An opening, space, or cavity, esp. a tubular cavity; a vacuole.

||Lu"men (?), n.; pl. L. Lumina (#), E. Lumens (#). [L., light, an opening for light.] 1. (Photom.) (a) 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. (b) A unit of light flux, being the flux through one square meter of surface the illumination of which is uniform and of unit brightness.

2. (Biol.) An opening, space, or cavity, esp. a tubular cavity; a vacuole.

• (Physics) In the International System of Units, the derived unit of luminous flux; the amount of light that falls on a unit area at unit distance from a source of one candela. Symbol: lm
  
• (anatomy) The cavity or channel within a tube or tubular organ.
  
• (botany) The cavity bounded by a plant cell wall.
  
• The bore of a tube such as a hollow needle or catheter.
  
  Swedish
• lumen (singular and plural)