Strange transparency issues in arnold 5


Hi All,
I have a strange situation where I have created a simple polygon shape with a glass shader and the normal arnold tag with the opaque option displabled.
Behind this I have another polygon shape with a mesh light tag which uses an image as its source ( for a TV Screen), but the mesh light does not show through the glass shader.
A third object with with a wood shader is placed behind the mesh light and this can be seen through the glass shader, even though it behind the mesh light???

I’ve attached 2 screen shots.
one with the glass object active, where can see the mesh object slightly to the right and a second with the glass object inactive, showing the mesh light in front of the solid wood pillar.

Im running Arnold 5 C4D

Any help with this would be great.



Looks like you might need to crank up the transmission ray depth or AA in the settings or in your camera?

Edit–thast not it–I can see that the cabinet is still visible.
Maybe take a look at the object with the city pic. Maybe something checked/unchecked on the arnold object tag for that object>


Hi Joel,
All the usual options are ticked, light visable etc.
I tried link a shader to the mesh lights colour instead of connecting a texture map.
It’s strange it works exactly how I would expect if the glass shader object is not in front.
If i remove the mesh light tag of the object it can be seen though
its almost as if it needs a “seen by transparency” tag


I’m also curious to understand what’s the issue here.



it is very strange.
I wonder if you would be able to set the scene up on your machine and see if you get the same results?

Three rectangles /blocks, one in the background, one in the middle and one in the forground.
The background block has a simple standard shader on it ( I used a wood effect)
The middle block has a mesh light tag with texture map in the colour slot witht light visable ticked.
The forground block has a standard glass shader with an arnold tag and the opaque option unticked.

I then angled the camera so I could see the middle and background block through the glass shader with the middle block slightly right so it could be partly see without the glass shader in front.
This way I can instantly see the mesh light is working.

I set the transmission samples in both samples and ray at 10 ( very high) but still the mesh light cannot be seen through the glass shader?

Thanks for any help you can give with this



Hi, Adam,

I actually did a test when I posted and I was puzzled as you by the result.
Then, in a second test, I tried with a simple geometry as a mesh light (no textures this time) and the result is again the same:

The Spiral, in this case, is a shader with the emission on. But, like in your case, the plane is a mesh light.


Yep, I also tried emission and could see it too.
It’s as if the mess light needs a “seen by transparency” option, like what you can set when using a background object with an Arnold tag.

Maybe it’s just a bug and will sorted by solid angle


Just use an arnold mesh light object and assign the plane to it.

Works fine here:

Tested with an arnold mesh light tag, works as well: