Definition - What does Luminous Flux mean?
Luminous flux is the measure of brightness of a light source in terms of energy being emitted. Luminous flux, in SI units, is measured in the lumen (lm). It is a measurement of energy released in the form of visible light from a light-producing source. Luminous flux is often a criteria of light bulb comparison.
Luminous flux is also known as luminous power.
Techopedia explains Luminous Flux
Luminous flux is often mistakenly thought to be same as radiant flux, which is incorrect. Luminous flux is the energy measurement of visible light, whereas radiant flux is the total electromagnetic energy released by that source of light. Total electromagnetic energy includes all the visible as well as non-visible radiation emanating from a source. Luminous flux interprets the sensitivity of a human eye by taking the power of each wavelength present in light. A luminous function is used to describe the eye’s response to each wavelength.