Hi there, how low was the new bulb ? Aside from a burn it might be fungal but for now get some silver sulfadiazene cream for it,you can put some on the shedding area to help it come off more quickly + then you'll see if there are more affected areas. Avoid baths for now and be sure his temps. are good, 80 cool side, 105 hot side. And yes, if it gets worse or you see no change after a few days see about getting to an experienced only reptile vet.