rule of thumb if you can hold your hand between the light and the little lady with no discomfort then you have just ruled out light burn also t5 are meant to get close safely and is it on the top of the plant our lower if lower then its really ruled out..so its time to do a few things check for bugs..(mites or scales) are you over watering before you water next stick a finger in deep don't water til its dry. it could be a burn spot from splash back(when watering) check your ph it could be blocking nutrients(calcium)...lack of potassium can cause tissue necrosis(dead spot)...some things to look into hope something helped..My plants are about 2 weeks old and are still under t5s, one has a small brown spot on it, i raised the light cuz i thought it may have been leaf burn. can anyone confirm?
thanks