Luminous flux is the visually weighted counterpart of radiant flux, measured in lumens. Its value depends on the optical spectrum and the specified visual response; it is distinct from radiant flux in watts.[ref]
The lumen is the International System of Units unit of luminous flux: . A source with constant luminous intensity within a cone of solid angle supplies into that cone. A source with the same luminous intensity in every direction supplies over a full sphere. [ref]
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Luminous flux is a measure of the total amount of visible light emitted by a source per unit of time, and it is quantified in lumens (lm). It represents the perceived power of light as seen by the human eye, taking into account the sensitivity of human vision to different wavelengths of light, which is characterized by the luminosity function.