The light doesn't seem to traverse through glass as you would expect in real life.

[Karol.Osinski]

Hey everybody, me and my collegue at work trying to figure out how to get our glass objects (mostly big chandeliers) to be illuminated properly. So far we are getting really mixed results which often have to be fairly boosted during the post. Usually when I don't get enough nice highlights and enough illumination from the lights supporting a glass / polycarbonate panel or a chandelier I counter it by mixing specular pass and light select pass inside the Photoshop and it works in most cases. I have very strong sensation that the light inside VRay does not interact with glass material as you would expect it in reality, it is often visible ONLY where it starts and disapear instead of highlighting rest of the glass. I wonder if it's matter of lack of enough geometry ? I also tried turning on caustics and setting them up properly but they doesn't really lit the glass itself. I have attached few examples of it.

[Karol.Osinski]

Is it the fact that 3D object is mostly EMPTY ?

[^Lele^]

Empty, in this specific case, ought to be allright: a ray would travel without bending until it meets the other interface.
You may need very very high bounces count, have you tried that?

[Karol.Osinski]

Honestly I haven't got time to do some extensive testings myself. I gotta setup the simple scene and all soon. Do you mean GI bounce count or the max refraction depth?

[^Lele^]

Refraction and reflection both, yes.
You may also have to try and add caustics (photon mapped, not GI) to achieve a specific look.
Not entirely ideal, and not quick, but it would work, i reckon.

[^Lele^]

Actually, it's very similar to the kind of job kosso_olli does with his cars' headlights.
I'm sure he'll be able to share some tips.

[kosso_olli]

Well, this is indeed quite similar to some parts of a car headlight. In a situation like that is is not so much the light traveling through the glass, but more the light inter-reflection on all the front- and backsides of the glass parts.
I see two crucial elements in getting a convincing result: Geometry and shaders. All the glass parts should be modeled correctly, meaning they are solid and have a front and backside. Also, make sure they have tiny chamfers and fillets where the light can create a nice highlight on the edge. If it is too hard to model, then use the edge texture to create round corners. For the shaders, make sure it is set to double-sided and reflect on backside. Also, make the reflection and refraction slightly blurry (0.98 or something is enough. That way, a result close to these rendered headlights should be possible. The illuminated C-Shapes in the headlights are lit from behind, the lights source itself is outside of the view the spectator.

[^Lele^]

Thanks Olli!
Btw, nice pictures. Now, can i see the renders? XD

[PIXELBOX_SRO]

OMG i woudl have bet those are photos, especially the BMW.
How do you get the model so precise? Do you get it from BMW? Or do you model it from a real world object sample?

[kosso_olli]

The first image has some more postproduction applied, becaue in the original shot there was a guy standing in front of the car. You can see him on the left. Also, some chromatic abberation as well as some dirt and speckles was added, because the same was in the original plate.
The second one only has some color correction and contrast. The headlights we get are mostly very detailed, depending on the manufacturer. Some companies do it better then others. In very rare cases, we had to remodel some parts.

[Buck]

What I see most often when someone is having trouble getting glass objects to look right, is they are assuming the glass is perfectly clear and shiny, so they don't put any texture or glossiness on it. Which is rarely the case in real life.

A hint of imperfection (glossiness and bump), and even some very subtle diffuse with some texture maps goes a long way to making something look real, that you would otherwise assume has no texture. That, and increasing the reflection/refraction traces, and turning on "reflect on back side" usually helps too.

[Karol.Osinski]

Hey, sorry for the late response, I am doing thousand other things at the same time like of most us here I suppose.. Anyway, thanks guys for your input, ^Lele^ for bringing kosso_olli and his awesome renders. Man..I honestly thought that the first two are real photos...wow!

• I lowered refl gloss o 0.9 and refr gloss to 0.97 which definitely helped a little.
• I checked specs of this particular chandelier and insterted all the 172 little IES lights in places where they approximately should be.
• I tried with photon mapped CAUSTICS but the only caustics I could achieve were the ones everywhere OUTSIDE my chandelier, there was literally nothing *bouncing* between the elements, even on the golden parts... - so no luck here..

What bothers me is huge render time difference between the two and very little visual difference. I believe the results with 7 bounces could be easily compensated with LightSelect + Glossiness render elements comped in Photoshop with similar results..

The only light source outside the chandelier bulbs is a simple, neutral room HDRI.

[^Lele^]

Well, wow to the lights count.
It's going to take a while to render, and you will have that time to thank adaptive lights, for it to not take the age of the universe^2.

Because it'ss modular, i think you'd be better off trying to figure out one element first, and then (if possible) extend that to the rest of the chandelier.

You would need an insanely high photon count to get all lights to cast caustics, i don't think it's doable with the tech we have right now (Besides the rendertime, it'll eat your RAM up well before you'll get pleasant results).
dian.nikolov may at some point want to try that scene out for his new caustics engine, i'm sure.