How many Lumens are actually useful?

I was reading on another forum where someone said that marijuana cant really use over 7,000 lumens per square foot? So using more would just be a waste of electricity.
Anyone now if this is accurate?

I need to upgrade my lighting (currently 150 HPS) and was thinking of adding a 400 watt HPS to go along w/ the 150.

After reading this and doing some quick math it seems like it would be a waste.

My closet: 2X3 = 6 sq. feet
7,000 lumen x 6 = 43,000 usable lumen

the 400 watt has 50,000 lumen, and the 150 has 13,000
So by this theory the extra lumen would be wasted? I find that hard to believe.

any help?

Lumens is just a way to relate what we need for folks that don't understand and most lights put it on the label (though they tend to exaggerate) what matters is PAR and SPD of a light but that gets technical

you will be fine, a 400 is great for 6 sq ft

you will only have to deal with the added heat