you are not making it very clear, what it is you want. I looked at terraria on youtube and don't see what you mean exactly.
I think you just want to add a darker layer on top and using blend-modes make sprites attached to your torches to see the layer beneath as if it isn't darkened.
Her's a (not so very good) example, it's just to show what can be done, please look at the blendmode-example provided with C2 to learn more about blendmodes:
Very simple and bad example