area light + shadows + gi = no specularity on glass


On this scene I have disabled shadows on my area light because, due to the camera angle, shadows hardly show up anyway:

But when I turn shadows back on to compare the difference, and enable GI to make them render faster, the result is no specularity on the glass:

If I disable GI (but keep the shadows enabled), specularity reappears on the glass:

Most curious.

Not a problem at the moment, since the scene looks fine and renders fast with no shadows enabled, but I’d be bummed if I wanted quick soft shadows to show up and had to lose my glass specularity in order to get them.


Hi Mark-
Can you post your project somewhere so we can look at it?



Here’s the collected project:


I just noticed that enabling GI also affects the refraction.


This looks like a GI related bug, to me.
I posted your project and a bug report over at EIAS3D
We’ll see what the Igors say about it.



Sweet. Thanks!


For a workaround, you could use the layer shader to render only the Specular for the scene (with GI off) then composite this in Photoshop with a full GI/ RT soft shadow render.



Good point! If I do another angle, I’ll probably have to do that. For now, though, I don’t even really need the shadow since from this angle it’s nearly invisible anyway.

Thanks for the help!


Nice looking glass Mark. I find myself looking at it a second, and third time. Can you share your glass material setup and lighting if you haven’t already somewhere else.




I talked about it a bit in another thread a few weeks back, but it’s pretty basic really. One main light, which is an area light, and a spotlight putting the highlight on the wall. Nothing fancy about the glass settings, but I do always make sure to use low reflectivity values for glass and liquid objects — sometimes even zero — with a Fresnel value to drive up reflectivity at the edges. The Fresnel value to me is important.

I posted the project above, so you’re welcome to download it and poke around.

It might seem like I have the raytrace recursions really high, but it needs to be high considering that I have four overlapping transparent objects.

One thing EI could use is some transparency absorption controls. Volume transparency doesn’t give the same effect, unfortunately.

But I love the look of EI’s renders. I have this same scene in modo, but modo’s renders, while very realistic, always seem to lack warmth and magic, if you get my meaning. Plus modo’s anti-aliasing is just terrible. I’m constantly fighting with it and always end up with ugly artifacts in transparent objects. The EI render just looks so lush and warm and seems to have weight to it, and the anti-aliasing is nearly flawless. Very nice.


Oh, I should mention that I have two vertically-oriented luminous planes in the scene which serve just to add specular highlights to the glass — a white one on the left, and a green one on the right. Really adds some beauty, I think.


Good looking project!

I wish everything had EI’s render quality…it’s so forgiving when jobs need to be done quickly. I really find the interface and just general work-flow for GI and the newer features, feeling very awkward to use.

Give me EI’s output quality and hi-res with Modo’s IPR and speed (for some stuff) I’d be very happy. Modo’s material system is such a let down…powerful but so kludgy and so busy.

Oh well, don’t mean to turn this thread into modo bashing:-). Good work, Mark!


Anytime I need something done fast with killer quality it’s EI I end up using. Every damn time. And usually I don’t even need GI.

I’m so with you on modo’s materials system. It actually hurts my brain sometimes just scrolling through the hierarchy trying to find what I’m looking for.

But those modo previews.
(Yeah, but that Trucoat™) That’s its killer feature for sure. Every 3D app should have that.


I agree every 3D app should have that…been checking out Octane. Looks like it might be worth investing some time into it.


Yes! I’ve been eyeballing Octane ever since I first saw the videos of its interactive previews. The DOF preview alone is mind-boggling.


Hi Mark,
The Igors have confirmed the bug and it has been fixed (for the next official release).
They also said that it only happens when GI shadows are on and transparency is 0.00.

So a valid work around would be to use a non 0.0 value, like 0.005

Good luck. :wink:


Fantastic news! Thanks so much for your help!


Just checked out your website! :bowdown:

Your one seriously talented artist. I love how you capture the lighting in so many of your paintings. I particularly like the portraits and the beach scenes. Have you ever had an exhibition? If not you should consider having one! :arteest:



Thanks, Michael — that’s really cool of you to say.

I have had a few casual shows over the years, but I have this a tendency to avoid forced social situations, so I haven’t been compelled to pursue that sort of thing even though I know it would probably benefit me. Plus I don’t really feel like I’m breaking new ground with my work. But I do realize that an artist is usually the worst judge of his own work!


Probably somebody has posted this already:
But the advantage is that it could work with Camera!
Real time feedback instead of those dozens or hundreds of test renders.