What are Lumens?

What is the lumen value of led?

Lumen, which is the unit of expression of luminous flux, that is, the energy that the light source perceives from the human eye per unit time. The symbol is Φ, 1 lumen is equivalent to 1/680W of the energy of the monochromatic source radiation.
(1) Luminous flux (φ) The light source radiates energy to the surrounding space in a unit of time, which is called the energy generated by the human eye.
For luminous flux. It is represented by the symbol φ, and the utility unit is lumen (lm), referred to as stream. The number of lumens emitted by the unit's electrical power
(lm/w) is called luminous efficiency.
Lumens are: 1 International lumens of light on a plane with a distance of 1 cm and an area of 1 cm 2 is 1 lumen.