You'll have to run a thicker wire if you're going to run a household hundred twenty volt
porch light. The little 12-volt wire will never handle it.
The idea of having something with batteries in it sounds like a good one. With today's LED
lighting I bet you can find one and then you won't have to drill anything. Or better yet maybe one with a little
solar panel built into it that will recharge itself like those walkway
lights do. I bet you can find something like that if you look around.