In essence, lumens are a human perception-based unit of brightness measurement. Different from humans, plants “perceive” light in different ways. The light necessary for photosynthesis may not always be bright.
It’s time to move on from lumens to a concept called “Light Quantum Flux Density” (PPFD), which represents the density of photons that arrive at a certain area.
To find out how much light energy is used for photosynthetic processes in your plant, you need a quantum flux meter. Make sure you select a quantum flux meter made especially for LEDs while testing LED grow lights, or your measurement may be blocked. Sadly, the cost of these gadgets is rather high.