Changes to lights in LightMix causes weird colors to appear

[Alex_M]

Using LightMix causes weird purple and yellow colors. Please see the screenshots below comparing the original lighting to the one changed with LightMix.

Render settings are pretty much the default ones. My lights are pretty simple - a dome light with no texture, a V-ray sun and a couple of disc lights in the powder room. The changes in LightMix are not too drastic too. V-Ray CPU renders fine with LightMix and the feedback after changing a parameter is instantaneous unlike the GPU engine where the image goes black for a few seconds before it starts rendering the new change. Every time I decide to start using V-Ray GPU for production work, I'm reminded why I don't use it. I hope that it doesn't sounds too harsh, but my honest opinion is that in 2023 it still feels like an unfinished product whereas the CPU engine has always been rock solid and dependable.

[hermit.crab]

Best you send the scene so we can take a look.

[Alex_M]

Hi Aleksandar,
Thanks. I've just submitted a ticket with number #77269.

[vladimir_krastev]

Hi, please excuse us for the delayed reply. We have examined your scene and found the problem. If we use Physical Camera Exposure Control along with LightMix and GPU as in your scene, an error occurs in the light selects for the lights and that is where these problems come from. The lights don't add up correctly in the light mix in short. A workaround is to use the VRay Exposure Control in 3ds Max's Environment and Effects instead of the currently used Physical Camera Exposure Control or to use VRayPhysicalCamera in the scene.
The issue has been described and forwarded to our developers. It is logged under VMAX-12977.

[Alex_M]

Thanks a lot for the explanation, Vladimir. I will try to remember this.