Could you please provide a link to github commit so we could integrate the fix into 5.3 branch locally 
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Unfortunately we don’t have a git commit for that particular fix in our release stream, however the target fix is slated for 5.4.
If that changes however, I will certainly let you know!
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Honestly it’s been a bit depressing. I don’t think there was a single GPULM release since the first time it was introduced to the engine which didn’t have some complete dealbreaker bug. We then had to wait for a next major version (not just hotfix) which fixed the bug but introduced another dealbreaking one.
I mean sure, GPULM is still experimental, but it would be great if the fixes for the dealbreaker bugs could make it at lest into hotfix version so there’s at least one version users who rely on high quality baked lighting can hunker down with until another relatively bug free version appears. So far that’s not been a case even once 
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It’s truly a pleasure to have you so active in the thread; thank you very much.
As @Rawalanche has pointed out, that’s a sad but true truth. So, I’ve decided to give the official Epic GPU Lightmass another try after a few years without testing it because it didn’t meet my needs. I’ve been using Luoshuang’s instead.
After several tests, I can provide some feedback to see if we can finally make GPU Lightmass (GPUL) usable and valuable for everyone. I also have some questions, please:
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Luoshuang’s GPUL is more accurate (if only slightly) and faster than Epic’s. How is it possible that a single individual, 5 years ago, and in less time (and during sparse time), created a more powerful, faster, and versatile GPUL (compatible with GTX) than a fulltime team of valuable people at Epic?
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Why is GPUL only compatible with RTX cards when it’s demonstrated that it could have been compatible with GTX cards? Even if RT cores were used as an argument for significantly faster results, they aren’t utilized.
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Why is it still in beta after so many years? What’s missing? What are your current main goals or primary concerns? Any estimate for a “Production” release?
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Please consider building reflection captures when pressing the build button.
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Please remove the annoying message about not using the latest lightmap UV algorithm (and when you instinctively press “Yes,” something in the scene often breaks… better not to show that message).
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Please include presets like low, medium, balanced, high, very high…
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I’ve noticed that on certain objects with “tight” textures, there’s a lot of noise in your GPUL, but significantly less noise in Luoshuang’s. In fact, I’ve seen this occasionally happening in UE5 even with Luoshuang’s GPUL. In short, I believe there might be something “off” in the way lightmaps are encoded. Possibly, if this “lightmap storage” detail is corrected (or reverted to UE4 method), it could greatly reduce noise on meshes, also in darker areas, whete GPULE is quite dirty. (Look at the lamp):
GPULLuoshuang:
GPULEpic:
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Some objects exhibit incorrect light bounces. (Look at the picture in shelf):
GPULL:
GPULE:
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In the previous comparison, look at the differences in the armchair shadows, like having quite different source angles in the Directional Light.
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Some scenes produce absurd results (bigger spheres are Movables, just to test Volumetric Lightmaps):
GPULL:
GPULE:
If you want these scenes to test, please, write me a PM.
Thank you and best regards!
@Matthew.Ivey Is it known that GPULM is completely broken on Landscapes?
One problem for putting in quality presets is that quality depends on how much light is in your scene.
On the titanic, I can bake an outdoor deck scene with 512 samples and it looks great. Perfectly clean.
On some of the interior spaces, I need 35,000 samples to get a similar amount of quality.
I noticed in the Unreal Roadmap there is an entry regarding adaptive sampling for Pathtracing. If there is any way this can be implemented for GPULM, I think that would be a big improvement going forward.
For your incorrect bounce problem, which engine version is this, and do you have the UE5-main fixes? I had this problem to an extreme until I compiled a custom engine version with the fixes.
Notice the light coming from underneath the machinery, which is just a solid floor.
While we’re on the topic of improvements.
I think there is still quite a bit of underocclusion, especially on thin meshes, which often will simply not have any shadow.
Perhaps this was changed in 5.2, where we had an overocclusion problem. There must be a possibility for a middle ground.
The ability to natively work with sublevels would be extremely helpful. I have been using a workaround of putting my atmosphere into a separate sublevel and using a different lighting channel so it doesn’t ruin the lighting in my main levels. This is a gigantic pain because I need to create “light blocker” levels, which are all the meshes around the level I want to bake that would affect the lighting of the primary level. I can set the lightmap resolution of those to minimum, but it still adds a lot of baking time, and making those levels is a big pain, since any changes made anywhere need to be manually propagated through all these light blocker levels.
For volumetric lightmaps, I put a temporary “light builder” level in the primary level that I want volumetric lightmaps for. This consists of the same meshes as are in all my sublevels, but all the lightmap resolutions are set to minimum. I bake my VL and then discard this sublevel. The VLs stay in the primary level.
GPULM seems to have a lot of problems with thin translucent materials. In this scene, Other than a few dim interior lights, the main light source in the scene is a stained glass window.
All this random noise goes away if I change the window material to Default Lit.
A super aspirational feature would be to have the ability to lightbake individual objects, like the way Vray for Unreal does it. That way if I discover a single lightmap is bad after doing a 30 hour bake, I don’t have to rebake the entire level after making the fixes.
Took a quick glance at the last pic of GPULE; what’s the reflectance value (BaseColor) of the walls? Did you try to run the scene in the path tracer?
Thank you @Ozykz for the info and the very useful suggestions. Mine was 5.3. For sure it will work better in UE5.4, I hope.
PS: Vray for Unreal allows per object? Why are you not using it? (Never used it before, so I want to know advantages and/or disadvantages, basically)
Nice to see you here @Luoshuang ! 
Actually those white walls (maybe it could be a good idea to modify the default material, with a more real-world white value) had the default value (0.9?) but I have tried right now with a value of even 0.7 (and I was ready to be wrong before, getting white lighting now), but the result it’s almost the very same; super green bounces and almost no shadows. Also tried with path tracing and it’s wuite green too, but not so exagerated:
Here you are the scene to test: 221.38 MB file on MEGA
Thank you (both) and best regards!
Vray for Unreal has not been updated for UE5. It is UE4 only.
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Ugh, this is bad: GPU Lightmass not working on Landscape
Can anyone please confirm that GPULM supports (or doesn’t) lightmaps on the Landscape ?
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@Miguel1900 @Ozykz I want to extend a big thank you to you both for the large suggestions you’ve posted above I’ve gone ahead and made notes on the suggestions so we can review them internally. I can’t promise anything of course, but we definitely appreciate the feedback/suggestions for everyone.
@motorsep We are watching this issue. I have reached out to the user to provide some additional info for us. We’ve created a bug to track that here for when it gets approved.
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Hi all,
There is an issue with Nanite Landscape which may affect Epic GPULigtmass as well
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Hi @Ozykz @Miguel1900 ,
Vray for UE5 is now available
V-Ray 5 for Unreal — What’s new | Chaos
UPDATE:- @Ozykz Just noticed in the system Requirement only 4.27.2 AND NOT Windows 11, found this myself, wont load trial.
V-Ray 5 for Unreal, update 1 - V-Ray for Unreal - Global Site (chaos.com)
I think this is Vray 5 for unreal, not Vray for Unreal 5. I don’t see anything about it being available for UE5 unfortunately.
Yep, Vray 5 for Unreal 4 
Anyway I never used it before, always preferred our beloved GPU Lightmass
BUT: I have noticed that “disperse” (light source with higer source raidius) lighting is quite broken in Unreal 5 (any subversion). This is not happening only with GPUL, but with CPUL too; it may be something related to the way Unreal stores the lightmaps now:
EDIT: Whops, sorry, I was wanting to publish this into the Luoshuang’s GPUL thread. This doesn’t affect Epic’s GPUL.
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I think they are too focused on Lumen. In their universe, baked lighting is obsolete - no one uses it 
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Yes… I have thought the exact same thing. It doesn’t seem it could be true, for a so big an important company, but it is… it’s like they only have 2 guys developing the most important and advanced (but broken) game engine in the world 
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Hi @Miguel1900 ,
I have been looking into this cant see why the
Photon Mapping is turned off in 4.26/4.27 BaseLightmass.ini
[DevOptions.PhotonMapping]
bUsePhotonMapping=False
bUseFinalGathering=True
in UE 5.3 and I believe all 5.X
[DevOptions.PhotonMapping]
bUsePhotonMapping=True
bUseFinalGathering=True
Last two days spent checking all the CUDA code is identical and thats true and correct
Whops, that’s true.
I have made some quickly tests with and without it (UE5.3 will crash if False) and there are some slightly differences… but I’m not sure which one is better.
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Heads-up - I was trying to apply this fix commit to 5.3.0, but compilation fails. There is no Substrate in 5.3.0, only Strata. So there were deep changes that need to be accounted for in order to apply this fix to 5.3.0