Bug: Light No Longer Passes Through Transparent Surfaces

[alessandro_boagno_design]

Note: This bug only occurs when using the new graphics engine.

To let daylight enter through windows, I’ve always modeled them like this:

• The outer face of the window uses a material with 0% opacity (fully transparent).
• The inner face uses a metallic-looking material that visually resembles glass.

This workflow has always worked correctly, but I recently noticed that light no longer passes through the transparent material.

The only way to get daylight into the room now is to delete the window face completely, leaving the opening empty. However, this is not a usable solution because I lose the glass appearance from the interior.

The same issue occurs even if I apply the transparent material to both sides of the window. The light is still blocked.

I also noticed something interesting: if I use one of SketchUp’s default Glass materials, light passes through correctly even when the material opacity is set to 100%.

This makes me think that something has changed in the way transparency is handled by the new graphics engine, and that the default Glass materials contain some built-in property that allows light to pass through, while ordinary transparent materials no longer do.

I created a quick test file to reproduce the issue.

• The box on the left uses SketchUp’s default Glass materials, and light passes through correctly.
• The box on the right uses my usual setup: one face with a fully transparent material and the opposite face with a metallic material. In this case, the light is completely blocked.

I also noticed another strange behavior.

The problem only occurs when there is an actual floor surface in the model.

If I leave “Display Ground” enabled and don’t create a floor face, the light passes through the window as expected.

As soon as I replace the ground with a real surface (a simple face used as the floor), the transparent window starts blocking the light again.

This additional behavior makes me think the issue may be related to how the new graphics engine calculates light interaction with transparent faces and scene geometry.

[alessandro_boagno_design]

Below I’m attaching the SketchUp test file, in case anyone would like to verify and reproduce the bug.

PROVA LUCI.skp (327.6 KB)

[Elmtec-Adam]

That is mysterious.

It was doing the same to me, but eventually I could get it to work

Then it stopped working!

[alessandro_boagno_design]

Exactly. The behavior isn’t always consistent, but what I described is the scenario that occurs most often.

I’ve also noticed that light sometimes passes through and sometimes doesn’t, depending on whether the surface is grouped or left as raw geometry.

On the Italian SketchUp forum, where I first reported the issue, we came to the conclusion that this is most likely a bug.

[AnnoNiem]

Hope this ‘bug’ can be solved asap

[ateliernab]

just to get it out of the way, it seems to work as expected on mac.
hey, we all have our bugs

AnnoNiem and Adam report having Nvidias in their machines, do you know what brand yours is ?

does it also happen if you’re above ground ? right now the floor is at altitude 0, if you move it all 10cm up, does it change anything ?
(trying to establish if it’s because of the “collision” between floor and ground level or if it’s just broken)

[Elmtec-Adam]

if ground level shadows are on, then it conflicts, the shadow casts differently on the ground than it does onto the face.

So you can see the opening on the ground, but not on the face.

You can get it to solve itself for a while by editing a group or making certain changes to the model and it remembers the opacity value, but it will just as easily forget it again.

[alessandro_boagno_design]

My PC has a NVIDIA GeForce RTX 3060

I usually work at ground level, but the problem shows up even if i move up