Lumen

lumen: see photometry.

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lumen

A unit of measurement of the amount of brightness that comes from a light source. Lumens define "luminous flux," which is energy within the range of frequencies we perceive as light. For example, a wax candle generates 13 lumens; a 100 watt bulb generates 1,200 lumens.

Lumen Ratings for Data Projectors
When choosing a data projector, the lumen rating is an important specification. In a darkened room, 500 lumens may be ample; however, in a conference room with normal lighting, 1,000 lumens would be better. In a room with daylight, 2,000 lumens is preferred. The standard lumen rating of a data projector is the average of photometer readings at several points on a full white image on the screen. See ANSI lumen, candela and spectrum.

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lumen [′lü·mən]

(anatomy)

The interior space within a tubular structure, such as within a blood vessel, a duct, or the intestine.

(optics)

The unit of luminous flux, equal to the luminous flux emitted within a unit solid angle (1 steradian) from a point source having a uniform intensity of 1 candela, or to the luminous flux received on a unit surface, all points of which are at a unit distance from such a source. Symbolized lm.

(science and technology)

The space within a tube.

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lumen (lm)

The SI unit of luminous flux equal to the luminous flux received on a unit surface, all points of which are equidistant from a point source having a uniform intensity of 1 candela.

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Lumen 

the unit of luminous flux in the International System of Units. Symbol, 1m. One lumen is the luminous flux emitted by an isotropic point source in a with a luminous intensity of 1 candela in a solid angle of 1 steradian.