This scene is illuminated by an invisible hemisphere with a special light-distribution function simulating ambient illumination like from a cloudy sky. Note that the forms are clearly recognizable and soft shadows are generated.

The above image was rendered with release 0.44 where the lighting is correct for the first time. All previous relases had produced more or less wrong results due to some errors in the program code. Finally they all could be fixed, and this image looks like it should now.