WordReference Random House Unabridged Dictionary of American English © 2024lu′minous flux′, [Optics.]- Opticsthe rate of transmission of luminous energy: expressed in lumens.
Collins Concise English Dictionary © HarperCollins Publishers::
luminous flux n - a measure of the rate of flow of luminous energy, evaluated according to its ability to produce a visual sensation. For a monochromatic light it is the radiant flux multiplied by the spectral luminous efficiency of the light. It is measured in lumens