it is from too much heat! i have seen this many times befoe. you must back the light off a bit or get more powerful ventillation fans. i'm gonna look through my old pics to see if i can post a pic for you to compare. if its on;y at the top of the colas then its most likely from excess heat. if it's happening in other places awAy from the lighjt it could be hermies. without pics you can't know for sure!