A Lumen (lm) is the International Standard (SI) of Units of the quantity of light of the Luminous or Luminous flux that is a measure of the total quantity of visible light emitted by a source per unit of time. The higher the Lumen rating the brighter the lamp will appear. 1 Lumen (lm) = 1 Candela (cd) x Steradian (sr) (A solid angle of one steradian (sr), from a source that discharges to an equal light in all directions, with the strength of one candela (cd)).

Reference Definition by Energy.gov/eere: A Lumen (lm) is an empirical measure of the quantity of light. It is based upon the spectral sensitivity of the photosensors in the human eye under high (daytime) light levels. Photometrically it is the luminous flux emitted with a solid angle (1 steradian) by a point source having a uniform luminous intensity of 1 candela. As reference, a 100-watt incandescent lamp emits about 1600 lumens.

Related Definitions in the Project: The Property and Unit