Question: what is the difference between radiant flux and luminous flux?
Answer: Radiant / Luminous Flux. ... Both Radiant & Luminous Flux represent the total power of a light source; however Luminous Flux factors in the human eye response. The unit for Radiant Flux is watt (W), and Luminous Flux is lumen(lm). An integrating sphere is often used to collect the light emitted in all directions.