I've had my two corns for 10+ years I've never given them any heat at all. I live in Colorado outside temps get pretty cold, and I've always been told there are wild corn snakes living outside in parts of Nebraska, And here in Colorado. Granted they are not active during the freezing months. They do survive though.
I personally keep the inside of my home at just under 70 deg. This is about the temp. at dusk where wild corns are found. So, heat is not needed unless you keep it quite cold. Light is only for you. The snake doesn't need it or even like it. My iguannas however need UV AND heat. For them, I provide a High UV mercury heat lamp. They are active only during the day, and sleep like rocks at night.