Light penetration is an issue. But the major concern you should have is lack of air flow, which causes bud rot and provides a perfect environment for other fungus and mould. This problem is made even worse when the ambient temp. of your grow room is high. So try and make sure there is sufficient fresh air flow (the tips of the leaves should bob up and down a tiny bit from the breeze). And try to reduce the grow room temp. whats your ambient temperature at right now ? Also make sure to trim off any dead foliage immediately as this will just give more things for mould/fungus to start on.