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I was trying to see how glass refracts light. I set up a scene with a conical light source facing a wall with a pane of glass in-between.

Direct conical light on a wall

Theoretically, the glass plane should refract to show an illumination on the screen (wall) with a lesser area. The schematic of the same is shown below. enter image description here However, Blender goes the other way and increases the area illuminated on the screen. This is not a physically accurate render for refraction. Am I doing anything wrong?

Refraction of the same conical light with a flat glass pane. Cycles renderer is spreading out the light. This is not how a flat pane of glass refracts light.

I have set up the node for the glass pane material as follows: Material setup

kichapps
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  • Transmission 80?? – Allen Simpson Jun 08 '22 at 15:45
  • Well, I just assumed glass would transmit about 80% of the light. However, even at 95% transmission, the result is qualitatively the same. – kichapps Jun 08 '22 at 16:18
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    It's a 0-1 scale :p – Allen Simpson Jun 08 '22 at 16:27
  • Oh damn! Results still look the same, oh well :/ – kichapps Jun 08 '22 at 18:28
  • I'm gonna say this is just another case of crappy caustics in cycles (fixed soon?). I have a number of posts on glass, here's a post with a bunch of info and testing, and a potential solution for you at the bottom - https://blender.stackexchange.com/questions/219303/glass-casting-shadows-and-not-looking-real/219957#219957 – Allen Simpson Jun 08 '22 at 20:46
  • Refraction is the bending of light rays when passing through a surface between one transparent material and another. In your case - it is a plate of glass ... What do you expect to see in your render? – vklidu Jun 09 '22 at 09:33
  • @vklidu, I expect to see the lit area to be smaller, however on the contrary, the result is having a larger area. – kichapps Jun 09 '22 at 20:47
  • Oh sorry for my blindness ... Try to use LuxRender as engine, it is also physically based but from what I spotted it could work better for this specific thing. You are right with Roughness zero the diffuser effect is weird. – vklidu Jun 10 '22 at 06:46

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