If I were you, I would ditch the light completely. All it does is dry out the enclosure, present an overheating risk, and blast light on your nocturnal pet.
A heat pad is fine, so long as it is REGULATED with a good THERMOSTAT. In fact, a thermostatically controlled heat pad is the preferred choice for most corn keepers. Just make sure you have a good thermostat on it!!! Without a thermostat, a heat pad can reach nearly 150*F... More than hot enough to burn, and even kill, your snake. You should have a thermostat (and a digital thermometer to monitor it) with the probe on the glass above the heat pad, UNDER all substrate, to make sure you're monitoring the hottest spot your snake can reach. Monitoring it from the top of the substrate layer is no use if the snake can still burrow down to a point that is 20-30*F hotter than the hottest the snake can safely tolerate.
My favorite thermostat is the Herpstat, though Alife makes a good t-stat for $30 if you're on a tight budget. Keep in mind, with thermostats, you really do get what you pay for. The $100+ digital Herpstat is FAR superior to the $30 analog Alife in quality and reliability. By the way, you can buy either of these two thermostats at The Bean Farm (
http://beanfarm.com/index.php?cPath=1238&osCsid=808e0573ba3155285b4a8eeec6b8ad6b).
Good luck!
