Definition of "lumen" []

• Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine. (noun)
• Physics The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions. See Table at measurement. (noun)
• Botany The cavity bounded by a plant cell wall. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Latin vocabulary of that time this external agent was designated by the term lumen while lux was used to indicate its mental representation."
• "They must be sealed to avoid moisture and kept clean to maintain lumen maintenance."
• "This conscience, unlike the voice of God or what later thinkers called lumen naturale, gives no positive prescriptions; it only tells us what not to do, what to avoid in our actions and dealings with others, as well as what to repent of."