lumen

lu·men

noun \ˈlü-mən\

plural lu·mi·na \-mə-nə\ or lumens

Definition of LUMEN

1

: the cavity of a tubular organ or part <the lumen of a blood vessel>

2

: the bore of a tube (as of a hollow needle or catheter)

3

: a unit of luminous flux equal to the light emitted in a steradian by a uniform point source of one candle intensity