The luminous flux, which is also a photometric quantity, represents the light power of a source as perceived by the human eye. The unit of luminous flux is the lumen (Im).
It is defined as follows: a monochromatic light source emitting an optical power of (1, 683J watt at 555 nm has a luminous flux of 1 lumen (Im). The lumen is an SI unit.
EXAMIANS
