I need to put some examples on the website for doing lava surfaces.
Here's one that uses two surface lights on the lava:
http://i.imgur.com/FAmAZlM.png
delay 2, light 20 for the fill light
delay 0, light 200 for the direct glow
If you use "delay 2" make sure to use low light values or you'll end up with a fullbright room.