I tested the two following parameters on a small file:
-Dcom.eteks.sweethome3d.j3d.PhotoRenderer.highQuality.globalIllumination=path
-Dcom.eteks.sweethome3d.j3d.PhotoRenderer.highQuality.diffusedBounces=3and got the following results:
compared to a rendering with default parameters:
If you turn on the light on the desk, I got the following results:
compared to a rendering with default parameters:
As you can see, if it doesn't give miracle results, the reflection of the outside light on the blue ground has some visible effect, but still an interior light gives correct results much faster.
For your information, here are also two images of the same empty room with default color on the walls and the floor:
again compared to a rendering with default parameters:
Did I do something wrong?
I don't know how complex can be the rendered scene. If you're ready to spend some time on this very time consuming task, I'll be pleased to read your report. 
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SimpleRoom.sh3d
(493856 bytes)
(Download count: 200437)
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Emmanuel Puybaret, Sweet Home 3D creator
