I recently received a 400W HPS light and am combining it with my friend's 400W HPS light for a larger yield. My question is: how many plants can we grow with this much wattage? Theoretically, each light should be able to cover about 16 square feet, but I'm not sure how many plants will fit in each square foot before they start blocking out light that should be going to the other plants. Just for reference, the strain that we're using isn't very dense, but does grow up rather tall. I guess the essence of the question is, how many plants can we grow with 2 400W HPS lights?