n. pl. lu·mens or lu·mi·na (-mə-nə)
1. Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
2. Biology The interior of a membrane-bound compartment or organelle in a cell.
3. Abbr. lm Physics The SI unit of luminous flux, equal to the amount of light per unit time passing through a solid angle of one steradian from a light source of one candela intensity radiating equally in all directions. See Table at measurement.
[Latin lūmen, an opening, light; see leuk- in the Appendix of Indo-European roots.]
lumen·al, lumin·al adj.
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