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I know a commonly duplicated question is "Why is light not passing through glass?" or "Why does my glass shader ignore lighting?", But mine's a bit different.

The Problem

I 3D modeled a type of weapon called a kukri in Blender, and I created a little display for it:

The speckles are the lighting emitted from the little spotlight-type things on the corners, I'm just running low samples at the moment.

As you can see, the shading looks dandy. Now let's see when happens when I put a glass cover on top of it:

Everything on the inside goes dark. Here's a representation of the geometry of the cover:

What I've Tried

I've tried the following node setups, neither of which solved the problem.

Here's my settings:

Download the .BLEND

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    $\begingroup$ IMO, the black contour are due to reflection and this is normal. Why don't you lower the thickness of the glass box? $\endgroup$ – lemon Mar 28 '17 at 14:16
  • $\begingroup$ I'd second @lemon. This looks normal. Is the glass not just reflecting the dark environment that surrounds it? Change the world to White or a brighter Gray and it should look OK. $\endgroup$ – Lewis Mar 28 '17 at 14:28
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Change clamp indirect to 0. You have it set to .01, which feels like it should only affect it in a small way but in truth the smaller the value for clamp the more of an affect it will have. 0 = off.

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  • $\begingroup$ This solved my problem. After a year of using it, I'm still not quite sure what Clamp does.. $\endgroup$ – Josh Silveous Mar 28 '17 at 14:42
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    $\begingroup$ @JoshSilveous, Clamp direct and indirect, as the names indicate, clamp all scene light values that exceed the entered value, one exception is 0, which means don't clamp, so when you enter 0.1 in Clamp Indirect for instance, that means that all lights information bouncing to Camera that exceed this value(0.1) will be scaled down to (0.1) value. $\endgroup$ – Georges Mar 28 '17 at 15:29
  • $\begingroup$ @Georges what value would you then recommend to get rid of the fireflies in my scene without removing the lights in the case? $\endgroup$ – Josh Silveous Mar 28 '17 at 15:31
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    $\begingroup$ @JoshSilveous depending on whether you're using standard Blender LUT or Filmic Blender (Wide Dynamic Range), I use the latter, I rarely use Clamps, but when I do, I usually set Indirect to around 10-14 direct always above 14.5, but each scene is different, it depends on your lighting setup, for standard Blender LUT, usually 3 for Clamp indirect, 6 for direct works fine, but you need to experiment with it, always try to use the less clamp (higher value) that removes the fireflies, overusing it will kill your lighting, quote:"Clamps are dangerous creatures". $\endgroup$ – Georges Mar 28 '17 at 15:38

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