lumen

noun4

1. •
   In the International System of Units, the derived unit of luminous flux; the light that is emitted in a solid angle of one steradian from a source of one candela. Symbol: lm.
2. •
   The cavity or channel within a tube or tubular organ.
3. •
   The cavity bounded by a plant cell wall.
4. •
   The bore of a tube such as a hollow needle or catheter.