Optimum, he can actually flower with probably only 2 total lights but there will be maybe a couple grams there in the end. And yes the 5000 lumens is per sq ft, not plant. The reason I said 4 per plant is so that one can be on each of four sides near the top, providing light all around. If you use LST, SOG, or ScrOG, you can get away with the current configuration seeing as you will have an even canopy and only need overhead lighting. I have 1 plant right now that's 2" under a 200w cfl (12,000 lumens) & has been LST'd to keep it in a 10"x10" area and that's not even proving to be completely optimum IMHO, although it's still doing great. The more light, the better generally. You can get a few of the y-splitters and run 2 bulbs from each socket as long as you don't exceed the wattage rating of the fixture.