Light or other artifacts - can't figure it out

[rmaytee]

Lately I have been having an issue and I can't seem to figure out what is causing it. Some scenes have the issue more than others. Some scenes don't have the issue at all, but it has been happening at least half the time. If you look at the included image, it is blasting some light noise in the center of the image. Where and how it happens has not been predictable.

For your information, here are a few things to be aware of:

1. All materials are v-ray materials
2. I have turned off denoiser so you can more clearly see the issue. Denoiser helps, but it does not eliminate the issue.
3. Using 3ds max 2025.2 27.0 - 27.2.0.20885
4. Using V-ray 6 2.1
5. Primary GI: Brute Force
6. Secondary GI: Light Cache Subdivs:1200, Sample size: 0.01
7. Image Sampler: Type: Bucket Noise, Threshold: 0.04
8. I have only v-ray lights in the scene. Some standard v-ray lights as well as a v-ray dome light and a v-ray sun outside the building

[Joelaff]

Try using light mix and the back to beauty render elements to see where the issue is occurring (a particular light or a particular pass of the render, like gi vs specular, etc).

Could be shadow bias on the sun or other light needs to be lowered. Make sure your walls have thickness, not just thin planes.

Could be caustics or even GI caustics from the mirror surfaces as well. Try disabling both types.

[fixeighted]

It does indeed look like caustics from the mirror, as you can clearly see the shape mirrored in the mirror and wrapping around the lamp shades.

[rmaytee]

Thanks guys. I turned off caustics and that didn't fix it. I turned off generate GI and that solved it. I don't know that that will always be ideal, but it didn't cause any issues with this scene.

[fixeighted]

Weird. Post a stripped down scene where it still occurs and we'll figure it out, as turning of GI isn't the best fix really

[Joelaff]

Try the animation preset (higher retrace) for Light Cache. Does switching secondary GI to brute force fix it?