Can i use a household 40 watt incandescent as lighting for my corn snake?

yes

I suppose you can, however, please stick with what the experts say. Use what your supposed to. Please. if you don't death is on it's way for your poor little snake.
Questions? email me at jessierox786@gmail.com
Thanks

You can, if your are on a budget, but it is not your best option. Corns don't really need light to thrive, they need heat so your purpose is best served a UTH (under tank heater) under 1/3 of the tank or a ceramic heat emitter above in a dome. The belly heat is best as it will aid the snake in digesting its meals and it can regulate its own preferred temp by crawling from the warm to the cool side whenever it wants. good Luck - I hope this helps