By calling it lights.rad you automatically make it a .rad file, no need to do anything else. But as you can see from the little screen shot I sent, your lights.rad works perfectly well on my machine. So there must be a problem at your end, and it isn't your lights.rad that is causing it.
The only other thing I can think of is that you are not actually finishing the RAD compile...or another problem is occuring before RAD. Email the log of any compile where you had the problem please don't post it here just yet, as I haven't got admin rights and can't edit it to just show the problem.