ray tracing produces strange darkness in rendering

Hi folks!
I just tried to render the model I was working on and it resulted in a strange problem. I activated radiosity and ray tracing. If I deactivate ray tracing there is no problem (exept for that the whole model doesn’t look very nice). But if I activate ray tracing one side of my box is strangely dark:


I already inserted a ton of lights but that didn’t change very much. The box consists of planes and circles. So the walls have actually no thickness.

There is another problem with this model actually. Maybe it has the same source: The inner walls should be completly white (with some reflections). But they still look a little like the texture of the outter wall.

Would be nice if anyone could help me with this problem.

If you wish you can grab the blender files and look at the “technical” detals of the objects here:


I had to compress it because it was nearly 30 MB (!?).

Have you tried merging doubles (selecting all vertices and clicking the rem doubles button in the mesh tools tab) or recalculating the normals? (selecting all faces and pressing ctr+n)

Yes you are right. Pressing ctr+n solved the problem. Many thanks BlackBoe.

When do you actually need to press ctr+n? Everytime you make some changes on the mesh?

Im sure blender has an algor. that tries to determine which direction to face the normal when you first insert a face, but its likely not perfect and get confused based on how you make the face. resulting in nor facing in inst. of out.

hm ok thanks. Will press the ctr+n from time to time in future.