Why in the world would you want to replace an LED bulb with an incandecent bulb? LED's are much much MUCH more efficient. They also cost much more to buy, and then you want to replace it with an incandescent bulb?? This makes absolutely no sense at all. If you want an incandescent bulb, buy a standard incandescent fixture. It will save you a bundle up front, though it will cost much more to operate, and you will have to change that incandescent bulb *at least* 10 times more frequently.
Anyway, it's the base of the bulb that you look at. If it's the same style base, it will fit, but the wireing may not be large enough to handle the incandescent bulb if this fixture was designed for an LED.