Clones with heat but no dark?

I'm getting a strong thermal pad and I was going to setup a place to put my clones on it...

They will receive some ambient light (it's my room) from me but I wasn't going to go to the trouble to actually put a CFL next to it...

I can if I need to, but will the clones survive with just heat?

Usually one starts with a low amount of light and builds up to the normal amount of light for clones. It's fine for now, but you should consider getting at least a desk lamp for it or much more in the future.