Some screenshots would help.
Maybe you can change the lighting channel of the buildings at runtime based on the camera position.
To turn off lights i would have used a direct line trace from the camera to the direcrional light.
its not very accurate/ you don’t get halos from it slightly dipping behind the planet, but turning it off based on its direct “visibility” is not a bad idea.
Another more expensive (performance with 4 lights and dynamic is already bad) solution that costs way less in time would be to set a sphere inside the planet that blocks the lights from getting through to the buildings.
The real issue is probably the same as we get with landscape and foliage. More often than not, that’s handled with a very large light blocking box set up under the terrain.
Thats because simply dimming the light is some times not enough.