I don't use bulbs for heat. I have UTH's or FlexWatt...if you do use a bulb for heat...be sure that the snake cannot come into contact with the bulb...this can and will cause some serious burns...also be sure to check your humidity...bulbs can dry the air quite a bit...although corn snakes aren't as sensitive to humidity...this can cause shedding problems.
Cornsnakes don't need natural sunlight, being that they are carnivores and get their calcium from their prey...the reason I provide light is so that they have what is called PHOTOPERIOD...this is a sense of day and night...cornsnakes are crepuscular, active mostly at dawn and dusk.
When the fluorescents go off at night (they are on a timer)...you can go down there about 15 minutes later and flip the room lights on...and sure enough they are ALL out and cruising around their tanks...like clockwork.