Spectral rendering for refractions

[kosso_olli]

Hey guys,
some materials are opaque to certain wavelengths of light but transparent to others. If you place a green glass in between a white light source and an outer red glass, the exiting light color becomes yellow/orange. A clever approach to use colored multi-component translucent materials to let e.g. the turn light shine yellow/orange when it´s turned on, while the tail lamp appears fully red from the outside when it’s turned off. I wonder if this is possible with V-Ray
The first test ended in a bad result, but maybe there is something wrong with the setup.

Here is the setup on a real car:



The technique applied to some other renderer:



And the test in V-Ray:




Regards

Oliver

[Joelaff]

Of course red and green light makes yellow. So makes perfect sense.

What technique are you using to make the glass red in VRay? It looks like it has some fresnel effect.

I am out of the office, but I would try coloring the refraction map. If that fails, color the fog, or try both.

But something tells me you likely already tried this.

The IOR looks different between the two samples as well??

I also wonder if a thin IOR 1.0 “gel” object placed on the inside of the red lens might help, or be necessary. But the other renderer looks great. What renderer is that?

[kosso_olli]

Of course red and green light makes yellow. So makes perfect sense.

What technique are you using to make the glass red in VRay? It looks like it has some fresnel effect.

I am out of the office, but I would try coloring the refraction map. If that fails, color the fog, or try both.

But something tells me you likely already tried this.

The IOR looks different between the two samples as well??

I also wonder if a thin IOR 1.0 “gel” object placed on the inside of the red lens might help, or be necessary. But the other renderer looks great. What renderer is that?

I tested both fog color and refraction color, in this case, the result was the same.
The other renderer is Vred which is very rooted in automotive visualization. They claim to be fully spectral.

[sirio76]

I would say that there's something wrong happening, on the back side of the red glass I get the yellow tint, on the front I see no light at all when using a green glass in between, Ill post some results later.

[sirio76]

Never mind.. I rebuild the shader from scratch and I get the correct result, very basic setup, white refraction and red/green fog color. I'm colorblind though so its possible I'm missing something..

[sirio76]

Are you using ACES?

[kosso_olli]

Interesting!
I still can not get this to work, the setup is the same as yours. We are not using ACES, though.

[Joelaff]

Are you both using the same version of vRay? Same version of Max?

[kosso_olli]

I'm on Max 2023.2.2 and V-Ray 6.00.20

[sirio76]

Are you both using the same version of vRay? Same version of Max?

No, I’m on Vray 6.1 on C4D but you should get 100% the same results, the setup it pretty basic.

[sirio76]

We are not using ACES, though.

I don’t use ACES neither, just standard linear image displayed in sRGB

[kosso_olli]

Weird, it just does not work. This is a test in Max 2024 with V-Ray 60.10.08.
White refraction, red/green fog color and a white sphere light behind the discs.

[kosso_olli]

Ah, I got it working. The trick was not to use pure red and pure green. Lowering the saturation led to this result:

[^Lele^]

Do not use full values for red and green.

edit: cross-posted

[fixeighted]

Is it as simple as the colours you're using for the fog?
I found that it does not work if red and green are both 255. Set them to 254 and it works.