In Yafray the standard clear glass material completely blocks light from getting through, even though it appears to be clear. So I can see the object through it, but the object is unlit if the light is on the near side of the glass.
Try using the caustics with the “full” GI rendering. Im sorry, this is one thing i dont know much about. I think this is the problem though, serch cuastics on blender3d.org… hope this helps
Can I let the shadow be weak behind the glass or does it need to be completely disabled by the method described above: “disable the ‘traceable’ button in the ‘Links and Pipeline’ panel of the material section”?