Definition and physical nature of luminous flux

Lumen (symbol: lm) is the main unit of luminous flux. It is a physical quantity that indicates the amount of light emitted by a given light source and is visible to the human eye. Lumen measures the amount of light produced by a light source, regardless of the direction in which the light is emitted.

Practical Use of Lumen

One lumen corresponds to a luminous flux of one candela (the unit of luminous intensity) uniformly distributed in all directions. A light source that emits more lumens is brighter than one with fewer lumens.

Lumen is used as a unit to specify the brightness of various light sources (such as bulbs, LEDs, and discharge lamps). A light meter, or photometer, is used to measure lumens.