from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
  • noun Biology The interior of a membrane-bound compartment or organelle in a cell.
  • noun Physics The SI unit of luminous flux, equal to the amount of light passing through a solid angle per unit time from a light source of one candela intensity radiating equally in all directions.

from The Century Dictionary.

  • noun An opening or passageway, as, in anatomy, of a hollow tubular organ: as, the lumen of the intestine or of a blood-vessel.
  • noun In botany, the internal cavity, or space within the wall, of a cell.
  • noun The unit of flux of light; the flux of light in a beam subtending unit solid angle where the source has an intensity of one hefner. See illumination, 1, and light flux.
  • noun The hollow tube of an operating-needle or of a hypodermic syringe.

from the GNU version of the Collaborative International Dictionary of English.

  • noun 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.
  • noun A unit of light flux, being the flux through one square meter of surface the illumination of which is uniform and of unit brightness.
  • noun (Biol.) An opening, space, or cavity, esp. a tubular cavity; a vacuole.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun physics In the International System of Units, the derived unit of luminous flux; the light that is emitted in a solid angle of one steradian from a source of one candela. Symbol: lm.
  • noun anatomy The cavity or channel within a tube or tubular organ.
  • noun botany The cavity bounded by a plant cell wall.
  • noun medicine The bore of a tube such as a hollow needle or catheter.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a cavity or passage in a tubular organ
  • noun a unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions


from The American Heritage® Dictionary of the English Language, 4th Edition

[Latin lūmen, an opening, light; see leuk- in Indo-European roots.]


  • 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.

    Lighting the Big Apple With L.E.D.’s - Bits Blog -

  • 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.

    Hannah Arendt

  • Commercially available units have broken the killer 100 lumens per Watt (lm/W) luminous efficacy barrier (the "lumen" is the standard unit of luminous flux-useful light output-while "efficacy" is the ratio of light output to power and measures the efficiency of the bulb).

    Ars Technica

  • Lifetime typically refers to the useful time of light output, also referred to as lumen maintenance.

    CE Pro Recently Filed

  • It is possible to have a considerable amount of plaque with no symptoms because the hole also known as the lumen allows complete flow of blood ... this amount can become enflamed, ruptured which then kills.

    WIBW - HomePage - Headlines

  • Lifetime typically refers to the useful time of light output, also referred to as lumen maintenance.

    Electronic House Recently Filed

  • Those who acknowledge the Divine also see and think this, but those who do not acknowledge the Divine do not see or think this because they do not wish to; thus they sink their rational into the sensual, which draws all its ideas from the lumen which is proper to the bodily senses and which confirms their illusions, saying, Do you not see the sun effecting these things by its heat and light?

    Angelic Wisdom Concerning the Divine Love and the Divine Wisdom

  • It also calculates metrics such as lumen output, lumens per watt, lumens per dollar and more.

    EE Times-Asia

  • Angiograms, images made by catheters inserted into the arteries feeding the heart, offer an inside view of the interior surface ( "lumen") of these blood vessels, often revealing deposits of a dangerous fatty substance called plaque.

    Health News from Medical News Today


Log in or sign up to get involved in the conversation. It's quick and easy.