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Epic's GPUlightmass

I think you can pretty much forget about UE4 and GPU Lightmass. It looks like UE4 is in basically maintenance mode and nothing will be improved/fixed unless it’s a crash. It’s safe to say we are gonna have to wait for UE5.x to get proper GPU Lightmass.

Known issue, no way to fix this right now as far as I know.

Darn, alright. Going back to CPU lightmass then.

Is there a way to build the lighting with CMD? There was that option with Luoushuang GPU lightmass

There are many problems, the main one is that some light sources are dark, increasing the brightness does not help, I suspect that due to the limitation of the amount of light to 256. How to get around this? In the documentation there is about it, but where can you remove the restriction?

Hello, I have a black mark LOD1+ behavior with GPU lightmass that was not there with CPU baking. Is that a known issue?


I created a thread explaining the problem:

Yes, it is (afaik for LODs generated in a DCC app). If you generate LODs in UE4, it shouldn’t have these issues.

I tried regenerating inside unreal (by changing the LODgroup to large prop) and the problem is still here.

Does the CPU lightmass uses only LOD0 and the GPU generates lightmaps for each LOD?

Edit: Keeping the object at very low lightmap resolution is the only way to prevent the black mark, but it is a shadow quality cost… I’m sad if I have to stick to CPU baking

That I don’t know. I have a feeling they made GPU Lightmass for archviz and never thought of LODs, which are mostly used in games.

I gave up all hopes of using GPU to bake lighting in UE4 and made peace with the fact that CPU Lightmass is the only reliable solution for baked lighting in UE4.

UE5 might be better, but I doubt that.

Just got this crash when encoding textures… Any ideas?


Rtx 3090
128gb ram

Any idea why the built in GPU Lightmass produces less quality visuals than the unofficial one?

Built in with settings bumped to a high number (3090, just before the crashing point)

Unofficial on medium, ignore color variations, this is due to post process

Unofficial was faster as well.

So, ignoring post process changes, just look at how clean Luoshangs unofficial one is, the built in version has artifacts, doesnt look as clean…

Hi, I’m finding the new integrated GPULM painfully slow. I’m running 4x1080ti in my workstation and was wondering if theres a way to:

Toggle the rendering GPU to non display gpu so I can get on with other work.

OR even better use multiple gpus for the calculation stage?

Using Loushangs GPULM you can run your cards in SLI to harness the additional power, but the new system is heavily dependant on RTX tech which no longer supports sli.

Being that RTX cards are seriously over priced and hard to get, im kinda stuck with this setup for now.

how do i install loushangs gpulm?

Gave 4.27 from git a spin and the VLM splotchy artifacts are still there. It therefore remains useless for scenes that are not 100% static.

Have you made a test case project to show Epic what’s going on and filed respective bug report ? If so, did they give it UE- reference number ?

I was trying to make a collaborative thread where share all our results and comparisons, evidencing problems to Epic Games, so they can focus on something, but no one has contributed:

Anyone else noticed a difference in light, translucency & reflections when comparing v26 and v27?
Still trying to figure if its something in my model. Will also read the changelog to see if this is to be expected.

why dont you just ebay your 1080s as they are over priced too… to afford an over priced 3090

does gpu lightmass still have a light limit of like 128 lights? Its useless if so…