[dagmx]

Some examples of Spectral ray tracers

Mitsuba is an open source research renderer with lots of cool features like differentiable rendering. https://www.mitsuba-renderer.org/

Maxwell has two spectral modes of varying accuracy. The more complex method is often used for optics. https://maxwellrender.com/

Manuka by Wētā FX is spectral and has been used in several feature films https://dl.acm.org/doi/10.1145/3182161 and https://www.wetafx.co.nz/research-and-tech/technology/manuka

[alkonaut]

If you want to look under the hood and find the big production ones like too complex, I can recommend peeking at this one. It's a great example example of just the minimum of a spectral path tracer https://github.com/TomCrypto/Lambda

[pixelpoet]

There's also Indigo Renderer and the open source LuxRender:

https://indigorenderer.com

https://luxcorerender.org

[dagmx]

Note that Lux isn’t spectral anymore. The older version is though.

[pixelpoet]

Funny, I added the original implementation of spectral rendering to Lux and then they took it out :D

[nextaccountic]

Why did they remove it?

[pixelpoet]

I have no idea (it wasn't exactly the same project, LuxCore vs Lux), and PBRT, on which Lux was based, later moved to full spectral rendering.

I guess they feel they'd rather reduce register pressure a bit than support it.