Heating Options

I have a few day geckos (2 enclosures of couples that were paired before I even got them, no worries there) but with winter coming up and it being a harsh one where I live last year, its about time I look into options for heating their tanks. What would be my best option outside of their heat lights?
Both tanks are 18x18x24 and already have proper lighting. A heating pad at the bottom of the tanks, but i feel like I could use a little more just to bump up the interior temp a bit more. Any suggestions would be greatly appreciated.

Check Amazon for reptile heat emitters.

The ceramic heat emitter bulbs will be more efficient and less drying than using regular reptile bulbs bulbs and go in a standard socket and reflector. They turn all the energy into heat instead of giving off any of it as light. There are larger infrared panels I have not gotten into. I mostly stick with the top heat infrared bulbs but humidity is usually not much of a concern for my species and they aren't demanding for high temps. Through the cold parts of winter I just added a small wattage regular light bulb to the cool side of my longer tank on a timer so it would warm up that side and the rock structure during daylight hours while adding some extra light. Rocks will then hold heat awhile after that so it didn't cool for anywhere near as long.

I also use ceramic heat emitters and love them. They really last a long time, much longer than any bulb. And they don't disturb photoperiod. Just remember that with any top-down heating, you need to watch out for humidity issues and spray more frequently if it becomes necessary.