How cold does your house get? In Winter, my cham room gets as low as 66F and this is not a problem. Some would say keeping it no less than 68F is better, especially for young ones. Better to heat the room in which the chameleon is kept, but if you cant do that for some reason use a ceramic heat bulb (emmits no light) as previously suggested.
One of my blog entries has quite a bit of stuff collected on lighting that you may like to check out