UE5 GPU Lightmass and CPU Lightmass getting different results

[ThinVeil]

Hi All, I was recently able to upgrade my video card after 2 years of waiting to an RTX card, so now I get to explore all the Ray Trace features I couldn’t use from 4.22 to 5.02.

I am on a quest on creating a mirror with nice clean reflections.
It started here in this forum asking about Lumen

Lumen GI and Reflections feedback thread

Hope this is the proper place for this. I’m trying to create a mirror in UE5. From what I have read and videos I have watched so for, it is difficult to do so. I can get close with Lumen GI and Reflection, but I have some noise I just can’t seem to get rid of. On the Screen left is the post process settings I have cranked these settings up and they don’t seem to do too much after a certain amount. [MirrorWsettings_01] Here are the Lumen views I know I have some surface cache issues, I don’…

too sum it up, Lumen isn’t there yet in 5.02 and the reflection from the mirror has artifacts.
I also tried Lumen with RT reflections and RT reflections doesn’t show dynamic GI.

I was then suggested to use good ole Lightmass with RT reflections. This is actually giving me (for the most part) the results I am looking for. (I don’t have to have dynamic GI.)

So now we have CPU Lightmass and GPU Lightmass. This is where my issues happen. I am using 5.02

I can’t find a reason why, but to use GPU Lightmass Epic Documents say to turn off Ray tracing features. So does that mean I can’t have RT reflections with it? That seems silly to me. I have left them on here.

I did force them off with r.RayTracing.ForceAllRayTracingEffects 0 to see and I am still getting the same resilts

It seems like with the GPU bake the indirect lighting slider on the lights is ignored. Is this a bug?

This example shows the differences between the two bakes GPU is the first one.

Again showing the differences The only stationary lights in the scene right now are the 3 lights on the fan. Gpu bake is the first pic

This is showing if I turn the indirect slider on the lights to 0.0 it is ignored in the GPU bake

So can I only do CPU Lightmass with RT reflections? Is that my only option?

[Arkiras]

@ThinVeil

I can’t find a reason why, but to use GPU Lightmass Epic Documents say to turn off Ray tracing features. So does that mean I can’t have RT reflections with it? That seems silly to me. I have left them on here.

This is not required. It’s only necessary to do this if you want to bake lighting with GPU lightmass but don’t want the other raytracing effects. The documentation could be phrased better.

@ThinVeil

It seems like with the GPU bake the indirect lighting slider on the lights is ignored. Is this a bug?

It’s not yet supported.

[ThinVeil]

Thanks Arkiras!

I totally missed that in the documents.
Then you just control the indirect intensity with the Post Process.

Awesome to know about the Ray Tracing effects. It seems like a lot of people are confused by that. There are YouTube videos where people are just forcing the effects off, but they never explain why.