| Lumen | ‖n.; pl. L. Lumina E. Lumens /plu>. [ L., light, an opening for light. ] 1. (Photom.) (a) A unit of illumination, being the amount of illumination of a unit area of spherical surface, due to a light of unit intensity placed at the center of the sphere. (b) A unit of light flux, being the flux through one square meter of surface the illumination of which is uniform and of unit brightness. [ Webster 1913 Suppl. ] 2. (Biol.) An opening, space, or cavity, esp. a tubular cavity; a vacuole. [ Webster 1913 Suppl. ] |
