lumen

American  

[loo-muhn] / ˈlu mən /

noun

plural

lumens, lumina

1. Optics. the unit of luminous flux, equal to the luminous flux emitted in a unit solid angle by a point source of one candle intensity. lm

2. Anatomy. the canal, duct, or cavity of a tubular organ.

3. Botany. (of a cell) the cavity that the cell walls enclose.

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lumen British  

/ ˈluːmɪn /

noun

1.  lm.  the derived SI unit of luminous flux; the flux emitted in a solid angle of 1 steradian by a point source having a uniform intensity of 1 candela

2. anatomy a passage, duct, or cavity in a tubular organ

3. a cavity within a plant cell enclosed by the cell walls

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lumen Scientific  

/ lo̅o̅′mən /

plural

lumens

1. The central space within a tube-shaped body part or organ, such as a blood vessel or the intestine.

2. The SI derived unit used to measure the amount of light passing through a given area per second. One lumen is equal to the luminous flux passing per unit solid angle from a light source with a strength of one candela.

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Other Word Forms

• lumenal
  adjective

Etymology

Origin of lumen

1870–75; < New Latin, special uses of Latin lūmen (stem lūmin- ) light, window

Explanation

The lumen is a unit of measurement for the brightness of light. If a light bulb is blindingly bright, it produces a lot of lumens. The lumen is a basic unit for measuring brightness, just as the gram is a basic unit for measuring mass. A typical light bulb in your home might produce about 1000 lumens. Lumen is related to the word luminous, which means “bright” or “radiant.”

Example Sentences

Lumen said it’s the first network provider to work on AWS Interconnect – last mile using Lumen Cloud Interconnect.

From Barron's • Apr. 15, 2026

Not long after, Brundage was chatting online with an anonymous cybersecurity researcher who then introduced him to Chris Formosa, an engineer at the networking company Lumen.

From The Wall Street Journal • Apr. 3, 2026

Lumen and Voyager both have negative earnings but trade at 0.6 times and 5.9 times estimated forward sales, versus 46 times for Palantir.

From MarketWatch • Mar. 16, 2026

“Kate Johnson’s recent open-market stock purchase reflects her continued confidence in Lumen’s long-term strategy and the value the company is creating through its transformation,” said a Lumen spokesman in an email.

From Barron's • Feb. 11, 2026

Mr. Lumen and his family stormed out of the room.

From "The Marvellers" by Dhonielle Clayton