lu·men noun \ˈlü-mən\
plural lu·mi·na \-mə-nə\ or lumens
: the cavity of a tubular organ or part <the lumen of a blood vessel>
: the bore of a tube (as of a hollow needle or catheter)
: a unit of luminous flux equal to the light emitted in a steradian by a uniform point source of one candle intensity
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