Rheostat is meant for reptiles. I use an actual dimmer switch. They sell them at Home Depot but you can buy them from actual reptile places as well.
Here is one actually sold from a reptile caging store.
http://cornelsworld.com/product/slide-dimmer-switch/
And here it is again at Home Depot... it is the exact same thing just cheaper at the hardware store.
http://www.homedepot.ca/product/cred...n-white/971428
It may not be a Rheostat (which is a dimmer in a sense) but they last and work.