Now I make all the walls static (and leave the enclosed cube dynamic). I would expect Unity to calculate the same light situation and simply apply it as a lightmap. Instead what I get is a proper dark room.
What you’re seeing here aren’t shadows; this is global illumination (GI). In reality, light doesn’t just stop once it hits something - some is bounced, some is absorbed, etc. In this case, the light you are seeing is ambient lighting from the environment/skybox. That doesn’t really make sense, because you can’t actually see the skybox from inside the room - no light can enter from the outside, so the room should be black. GI is fairly difficult to do in realtime due to the sheer amount of information processing required, so most GI has to be baked and can therefore only effect static objects. More recently some new realtime GI techniques have been proposed, but this is still emerging technology. If you want your dynamic objects to be effected by global illumination, you can use light probes;
You can think of these as small pre-baked panoramic captures of the scenes static lighting - place a group of them and a dynamic object is able to blend between the closest probes to approximate local GI.
Thanks @Namey5 ! I have been doing some more reading and experimenting in the meanwhile and mixing that to your answer I think I get it.
In the first case nothing is baked so even if my Directional Light is set to Mixed, there is basically no GI impact in the scene; at that stage it is behaving like a Realtime Light and therefore contributing only direct lighting to my Scene.
Then, when I set objects to static and go through the baking process, GI is applied. This contributes to much richer details (indirect light is now part of the game) and the scene looks darker. At this point changing any Ambient light setting will only affect Dynamic objects as the rest is just a texture.
So Answers are:
Because of the impact of GI which is visible only after baking the lights.
Because it is lit by the Skybox without GI at all. Apparently the Skybox only produces indirect light that it is not at all considered unless some sort of GI is enabled.
