Alright, this took me 1 min to set up, if you get the hang of the node based structure it isn't too hard.
Check out the image I prepared. The ramp is just a ramp with white-black range (you need to tweak it to your preference). The grid is where you put your file node (I didn't have a good one handy). You then multiply the ramps out-value with the files and you input that into the incandescence. Hope it helps. (the stucco is just for some color)

edit. You should perhaps clamp the surfaceLuminance, I don't know what valuerange it has, but it seems to work fine without.