Green leaves....

Why, out of curiosity, do you formula the WATTS per sq and not the lumens per square?

If I invented a special light that cast 8,000 lumens per sq......what would it matter what the wattage is?

Lumens are rated at 12" so why the wattage scale and not the lumen scale....?

Just curious thanks.
HARDDON Reviewed by HARDDON on . Light Selection Would 2 40w fluorescent "aquarium and plant growth" lights be good for 8 plants? Rating: 5