lumen

noun

Etymology: Borrowed from Latin lūmen (“light, an opening”). Use as a unit was first adopted by French physicist André Blondel in 1894.

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.