Today's Word of the Day means...
lumen lu·men (lōō'mən)
n. pl. lumens or lu·mi·na (-mə-nə)
The inner open space or cavity of a tubular organ, as of a blood vessel.
The unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.
Plural lumens or lumina