I completely understand the lack of light and leafs yellowing from it. I may be wrong, But I would find it hard to believe this is the case. The plants are really not that big yet to where I think it is a lack of light. They are under a 400w HPS and 2- 4' 2 bulb floros as well. I move the plant and rotate them 2 times a day to ensure good lighting to the whole plant.
I will keep an eye on it and report any changes good or bad.