Yeah the root thing is what pretty much stumped me last time.... I see some fair differences in growing in even amongst the plants in my waterfarms and could not tell you why that is ....ventilation as Bonger says? Yes, different types of plants grow differently and at different rates as well so without photo it's hard to say.....also which plants were closest to your light leaks? That may have something to do with it as well.

When i went to the hydro store the other day my guru told me that the way the "pros" do it for maximum lighting is measure the lumens or footcandles plus the temperature of the leaf surface. Anything over 80 degrees on the leaf surface itself will slow photosynthesis WAY down due to the heat produced and the stomata (sp?) will close. X-Crispi and I have been playing with this idea....you can buy little hand held temp gun for about $25... which my guru sold me by the way. I had actually gone there to talk to him about a cool tube so that I could get my light closer and he ended up selling me this instead.....about $100 cheaper but he swore to me this was a better way to do it and its $100 he lost on that so I believe him. Interestingly I found that I had guessed pretty well where my light should be (temps on leaf surface..76-78) so it might be something you want to think about. And seriously, for not having to guess where to put the light alone it was worth it to me.