Hello!
I've been using ceramic bulbs or infrared bulbs to raise te heat. Infrared bulbs shouldn't be used at night though (at least I don't think they should)... If you use ceramic bulbs, make sure you're using a lighting source with a ceramic or porcelain socket. The ceramic bulbs get very hot and will melt plastic sockets.
I do watch the heat though, I don't want to cook any of them!
I recently got a mini PVC covered greenhouse from Menards and I keep the heat bulb in the middle, underneath the plants. I pointed it down, and it's above some black pots of water. I have a fan angled so that the fan blows the water around, and the bulb heather the water all while raising the temps. The plants get a better amount of humidity and heat this way!
but it does take up space that I could have used for plants...