We have an old oven at home, and it uses the standard old 40W appliance bulb; I think those bulbs can handle at least 600 degrees Fahrenheit or more without a hitch. The glass probably won't start getting soft until well over 1200. No big deal, really - they are all glass, ceramic, metal (tungsten), and some sort of inorganic compound for the frosting. Although I'd bet I could easily melt one in my ceramics kiln.