- (n.) A unit of light flux, being the flux through one square meter of surface the illumination of which is uniform and of unit brightness.
- (n.) An opening, space or cavity, especially a tubular cavity; a vacuole.
- (n.) 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.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). lumen. Retrieved September 21, 2026, from http://smartdefine.org/lumen/definitions/2029181 |
| Chicago | Webster's. 2011. "lumen" http://smartdefine.org/lumen/definitions/2029181 (accessed September 21, 2026). |
| Harvard | Webster's 2011, lumen, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/lumen/definitions/2029181>. |
| MLA | Webster's. "lumen" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/lumen/definitions/2029181> |