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

Brightness is measured in lumens, with a larger number being better. —K. Thor Jensen, PCMAG, 1 Dec. 2024

This ultra-portable gadget twists out over 200 lumens of light and burns for up to two hours a charge while fitting in the smallest pocket on your daily ensemble. —New Atlas, 13 Dec. 2024

With a max brightness of 3,500 lumens, this projector can do the job even in the middle of a bright winter day. —K. Thor Jensen, PCMAG, 1 Dec. 2024

All of the best running headlamps on this list are 400 lumens or more. —Ashley Thess, Outdoor Life, 14 Nov. 2024

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

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