Thank you for the thorough answer, the example project works great! However I still have trouble with distant lights: The sun on one level is lighting up the other level and I just can’t figure out why that doesn’t happen in your project.
I copied the “Light Source” distant light from your project to my “day” level but the “night” level still got indirect light from it. This means that the light actor itself is not the problem, maybe a world or project setting, I don’t know… Could you think of anything which might cause this?