Hello my fine fellow Carrara friends!

 

Okay, so I'm wondering if there is a way to set shaders to react to lights.

For example.  Let's say I'm making an animation with a planet and I want to have city lights on the dark side, but then for the lights (which would be provided by a proper texture map) to be off when they face the sun.

Of course, I have figured out how to do this with After Effects and two render passes, but the thought has occured to me that there might be a way to do it with shader math that I don't completely understand.

Any thoughts?