lumen

noun

lu·​men ˈlü-mən 

plural lumens also lumina ˈlü-mə-nə 

1

: the cavity of a tubular organ or part

the lumen of a blood vessel

2

: the bore of a tube (as of a hollow needle or catheter)

3

: a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity

luminal adjective

or less commonly lumenal

ˈlü-mə-nᵊl 

Did you know?

There are two common units for measuring light, the candela and the lumen. Both are recognized as standard international units, which also include the second (for time), the kilogram (for weight), and the meter (for length). The candela is a measure of intensity; an ordinary candle gives off light with the intensity of about one candela. The lumen is a measure of "luminous flux;" a standard 100-watt lightbulb gives off 1500–1700 lumens. Luminous flux indicates how much light is actually perceived by the human eye. Technologies vary in how efficiently they turn electricity into light; halogen lights produce about 12 lumens per watt, ordinary incandescent lightbulbs produce about 15 lumens per watt, and compact fluorescent bulbs produce about 50 lumens per watt.

Examples of lumen in a Sentence

Recent Examples on the Web

This smart headlight is a serious tech gadget that packs a punch at 800 lumens. — Erica Zazo, Outside, 27 Mar. 2026

Portable projectors with more than 260 lumens have been known to struggle in bright conditions. — New Atlas, 18 Apr. 2026

This weather-resistant outdoor floor lamp can create a cozy atmosphere for your backyard living room, providing 40 lumens of soft light. — Bestreviews, Chicago Tribune, 16 Apr. 2026

Longcore said the issue mostly comes down to color temperature (measured in Kelvins) as opposed to brightness (measured in lumens). — Los Angeles Times, 8 May 2026

Word History

Etymology

borrowed from Latin lūmin-, lūmen "light, source of light, opening to let in light, aperture of any kind," going back to *lou̯k-s-men, earlier *leu̯k-s-men, from Indo-European *leu̯k- "become bright" + a concretizing suffix *-s-men — more at light entry 1

First Known Use

1873, in the meaning defined at sense 1

Rhymes for lumen

• crewman
• crewmen
• cumin
• human
• numen
• rumen
• suman
• acumen
• albumen
• albumin
• bitumen
• cerumen

Kids Definition

lumen

noun

lu·​men ˈlü-mən 

plural lumens also lumina -mə-nə 

: a unit of light quantity equal to the light on a unit surface all points of which are at a unit distance from a point source of light having a strength of one candle

Medical Definition

lumen

noun

lu·​men ˈlü-mən 

plural lumina -mə-nə  or lumens

1

: the cavity of a tubular organ or part

the lumen of a blood vessel

2

: the bore of a tube (as of a hollow needle or catheter)

3

: a unit of luminous flux equal to the light emitted in a steradian by a uniform point source of one candle intensity