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.