yea this is interesting, it seems that each light can only support so much growth, or yield. Apparently no matter if you have 1 plant (vegged longer) or 100 plants (vegged shorter) each light can only produce so much bud. In other words each light has a limit on the amount of bud it will support. This is why I bought another light, I only had 1 150 watt hps in a 2' x 2' closet, now I have 2 150 watters side by side touching one another.
Here is where it gets cool, I had 4 plants in there, so thats 1 plant per square foot. I recently made the blunder of killing a suspected hermi that was not a hermi leaving 1 plant under the light that had 2 plants directly under it. The plant that is not sharing a light has begun to grow much larger buds than the other 2 plants.
So I theorize that I did not cut my yield by 1/4, but in fact the bud that was going to grow on my other plant, is just going to grow on this one, which will have buds twice as large as 2 plants in the same space would have grown.
most places I read that 1 gram per watt (of hps) is a very big success and that in fact 0.5 grams per watt is more like it. Also I have read that if you do everything perfect you may even get up to 1.5 grams per watt, though I'm expecting 0.5 for my first harvest.