I don't know why people talk about light per plant. The best thing to do is 50 or better per square foot of grow space. Not per plant. Unless your talking cfl. Then you need more per plant. And your over all sun at the beach is right. If you have a 4x4 area and 4 plants in there. Each taking a 2x2 area. And a 600w light. That's 37.5w per foot2. So each plant is getting 150w. But if you use only 1 plant with the same setup. Just in a SCROG style. It will be a longer veg to fill the area but light is used the same. Now when it's harvest we measure by GPW. That's grams per watt. So let's say you get 1.5p total dry. That is 600watts divided by 672 = .89 gpw. This method dosnt change if it's 1plant or 100. not saying these are the numbers you will be getting just using it as a example. .4gpw is a good take.