Hi Cheryl......
If you're using a glass tank, I would suggest using an under tank heater, the kind that sticks to the glass underneath the tank. You just leave them on all the time.
I don't like using lights, it's too hard to control the heat when ambient air gets too cold or too hot.
If you place the heat mat under one side of the tank it will give the snake the option of the warm side or cool side.
Also, they don't interfere with the natural light cycle.