sunglass.blend (583.3 KB)
I think that glass panes have too much effect on light. The shadow of the glass panel should only be barely visible on the ground. Only the frame should have a dark shadow. Could it be that the light that passes straight through glass is not rendered and only scattered light is considered? Is that a bug?
Your scene is working as it should. In reality even glass absorbs some light and the result is looking right. Try building a wall around the window and you will see that it looks much more realistic. It only looks so strange because the environement you can see is completely lit with the direct light.
To add to this, usually in architecture renderings a simple transparent shader is used with a fresnel glossy shader for reflection on windows.
Real glass relies on caustics for energy transport. Since number of samples add up, you’ll have to use a lot of samples for the right amount of light to refract in it. Use this approach instead, close enough for glass with no refraction:
The curve is very close to glass IOR response. Using Layer Weight/Facing, you don’t have to worry about anything wrt fresnel inverting for the backface making weird shadows etc.