Ok, thanks for the explanation.

This seems to work a bit different than I am used to from DAZ Studio. There you had something called "Uber Environment2" which could be set as an indirect light source. I loved it for all kinds of night scenes. Therefore I just added an UE2, set it to indirect lightning, gave it a light blue tint and lowered the intensity to about 20%. This gave me a very smooth and even light all over the scene - perfect for moonlight.

But this was DAZ Studio. Now I am a Poser user and there is a lot new to learn.