Rainbow caustics? (Twilight Render V2)


My goal is something like this:

I can’t figure it out…



Rendered with Easy 10 - Interior+, still no rainbow caustics

Untitled.skp (50.0 KB)


This is the type of exploration that could eat up large chunks of your time…

Is Twilight a true raytracing renderer?

Does Twilight have subsurface light interaction?

With true raytracing, do the light rays “know” they are made of constituent RGB channels (let alone a full spectrum of color)?

If they do, does Twilight have the physics formulae to resolve interactions with light bending substances?


I did a test setup with my ray tracing renderer (Raylectron) and got nowhere.

There are very few physically based light characteristics available.

Possibly Vray may have more potential.


I’m not sure, but I made an emitter with red, blue, and green. :man_shrugging:
with sunlight
The caustics look colorful, but so is everything else…



Having more complex light quality in ray tracing renderers could lead to some powerful render special effects.

As usual though, work arounds like yours can be a very useful solution.

Did you deploy a precise color triad for your RGB - perfectly equidistant on the color wheel to achieve a balanced output?

Can you share a higher res image of the render?


What light beam are you using - laser?

What coverage angle of light?


I just used the red, green, and blue colors from the colored pencils in the materials. I wonder if there’s an IES light for download with colors included in the light rays.

I’m using an emissive surface split into 3 colored faces. Then I put a hole in a wall to narrow the beam of light. I should try to narrow the beam more…

Here’s the file for you to check out if you want.
Untitled2.skp (60.3 KB)


I am working on your model at the moment.

Just wondering if there are more 3D tools/systems that can be deployed to simulate RGB light being focused to a point of white light and then back to a spectrum…


Maybe it could be a laser made with emissive surfaces and a light hole… If you focused it enough, then it wouldn’t scatter colors everywhere.

For this scene, I increased the length of the light hole to narrow the focus of the colored lights.



For a large scene, you could use multiple handmade caustic lasers.
Kinda got it.skp (60.5 KB)


“Thea Render” has the capability to do this.

Unless you want to see the beams of light in the air, you can simplify the render by not using volumetrics. The spread of refracted light can be seen projected onto a surface. That surface should be a lighter color, so it acts like a screen onto which you project the light. In this model that surface is black which would make it harder to see.


Do volumetrics slow down the render time significantly?


Yes, it sure does as it’s a lot more information to calculate.
Not just for this application, but I’ve found in regular room or exterior renders there is a lot of “sparkle” in the air from the fog/global medium that can take a lot longer to resolve compared to not having that. So much so that at times it can be faster to emulate in post-photoshop augmentation.


Thea’s caustics look great! I downloaded Thea, but the installation process is too confusing. The installation reminds me of Kerkythea, which I got to work previously. Kerkythea was very confusing to use too. Then I upgraded my OS and it wasn’t compatible with the upgrade. Unfortunately, I might have to pass…


Thea came from kerkyTHEA, the new version V.2 has a much simplified interface, although I’m still using V1 until I get familiar with V2 as it is radically different.


Is there a guide on how to install Thea? I’ve installed it twice now and can’t find the application. The node folders showed up, but I don’t know how to use them. P.S. The node is a different installation than the app. I can find the node, but I can’t find the app. Is it a free trial or something?


there’s this, but not sure if it applies to the newest version? I’m on a PC so installation is different. I’m sure with a bit of digging you could find that help?


I got Thea to work! I guess the installation automatically installed it into the SketchUp Extensions. I found it when I restarted the program. Thank you for all the help!


@Forestr, I played with this for a few hours using IRender nXT, no matter how I set it it didn’t work.

In that SU is a surface modeler, I’m guessing it takes more than a few faces to create dispersion.

But I’ll be watching to see if you find a solution.


This interesting discussion (and the jewel globe) reminded me of one of my favorite projects as a software engineer: writing a ray-tracer. I’ve been interested in computer graphics almost since I started learning to program in 1977. A friend got me interested in ray tracing specifically in 1986 or so. I tinkered with the program off an on until about 2000 when my last addition was caustics, including dispersion. Here’s a sample image, which was lit with a single white spotlight. “Diamond” was chosen as the material because it has a very high index of refraction (something around 2.4 as I recall), and thus causes a wide dispersion pattern. I think the program computed 7 or 9 source rays each at a different wavelength to determine the lighting results, and relied on some averaging aspects of the algorithm to yield reasonably blended results rather than hard-edged spectral lines (which also cause the small-scale mottling).

And here is some fun with purely-reflective caustics:

My program is/was terribly inefficient and hard to use, but it provided me with a lot of good times writing it and creating images. :slight_smile:


Here’s the SU Thea render rough test I ran, one with medium one without. The one with atmoshphere took about twice as long as the other.
I used the sun as the light source passing through a series of holes to limit it to a narrow beam. Will work with a spotlight too.