are you useing tin foil it might be a burn from a hot spot caused by the way foil reflects light i have had that prob now i use white paint inside my grow box no hot spots also mirical grow soil retains alot of water careful its easy to over water also if your gonna go floro i use a 125 watt envirolite 39.95 as my main light source and 4 ft floro tubes [3]
good luck