Emit color when no light (opposite of base color)?

I’m trying to emit a texture I have that is basically city lights for my planet, but I only want it to appear on areas that don’t have light shining on them, ie the dark side of the planet. Essentially emissive color but with something that filters it based on light. But I can’t seem to find anything that let’s me “get how much light” there is. I’m sure it’s something simple I’m missing

Thanks for any help you may have!

Hey Pinworm -

Here is the basic setup and an added bonus of a spin mechanic for your planet:

If you have any questions let me know-

Eric Ketchum