If the room temperature doesn't drop below 75 F you can ditch the heat lamp and use a Under Tank Heater. (UTH) Heat bulbs are bad for humidity. UTH's don't effect humidity, but require a thermostat to control them and probed thermometers to monitor them.
Here is a thread that goes over this stuff in detail, and has links to recommended products: http://ball-pythons.net/forums/showt...t-Thermometers