Lumen GI and Reflections feedback thread

I am not sure I understand what you mean… Are the pyramids are shapes inside the cube? If you find some spare time to take a screenshot I’d be grateful - really like the effect! Nice and smooth

I compiled the current version of UE5 from source (Downloaded on 27.11.2021), and noticed that the performance of lumen has gotten considerably worse. (Comparison done at same settings/location etc. Will investigate further tomorrow.)

EA2 (FPS):

Current UE5 from Github (FPS):

Hardware used:
CPU: Ryzen 3700X
GPU: RX 6900 XT

That said, there are some visual improvements/changes.

  • less “noise” from emissive reflections
  • GI from subsurface materials is now stronger.
  • Light sources in general seem to be stronger? in comparison to EA2. (there sometimes is more “bouncelight” in direct comparison.)

Then there is this “Endless loop” of lumen getting brighter for no good reason (issue wasnt there in EA2 (ignore the broken UI-stuff, something got removed and UMG decided to stop working.)):

I was wondering if there are any plans of implementing Lumen into Composure. So far it seems that the Scene Capture pipeline doesn’t use Lumen.


this isnt a bug thats Lumens raytraycing having a too low sample size causing it to constatly squirm around

its fixed by increasing Luemns final gather amount to 8 or 16 in post processing volume or in the camera actor.

have you tried increasing lumens quality settings?

increase final gather quality and this goes away

this is ust because lume is default at final gather quality of 2, you need to rmap this to 8 or 16. The noise is literally because its a super low resolution sample count

Lumen’s shadow seems rather noisy. Is there any way to improve this? I’ve set the Final Gather to 16, and it’s still noisy.

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The error described in the following Post: Lumen GI and Reflections feedback thread - #194 by Yaeko
seems to be resolved in the current ue5-main build (downloaded 21st of December).

The issue from this post: Lumen GI and Reflections feedback thread - #48 by Yaeko
might be fixed too, at least I could not replicate it “the usual way”.

EDIT: Instanced Static Meshes are now properly working too, at least they are represented with their correct color in the lumen scene and do reflect the appropriate light color.

Off Topic: Holy Moly, what happened to cpu usage? My game suddenly eats away 80% on my 3700X, where it was using ~15% on EA2, at the same Framerate. (not lumen related?, just some rambling.)

2048 in reflection resulution in Project Settings. Quality of Lumen Reflection is set to 4. And I still get horrible reflections in Lumen. Why?

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Because this is what Lumen is at this point… a highly unreliable system that randomly breaks everywhere else than Epic’s demo. :sweat_smile:

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I’ll add to that: having just tested out UE5_main’s latest stable build, reflection quality is actually worse than UE5_EA2 or the Matrix demo. Not because they haven’t figured out how to achieve these high-quality effects, I just discovered that many of the CVars and quality handles are no longer actually working: I can’t access the higher quality levels that allow lighting look-up at the hit point. In addition, the engine crashes whenever I try to recapture scenes using reflection captures, so I’m kind of out of luck for achieving good quality short of just using the path tracer.

Not to bash epic, but even that is because epic deliberately built those demos to not expose lumens “broken-stuff”.

Or, to put it in different words: there is a reason that the matrix demo does not feature a single tree, neither does the initial ps5 demo, or the one released alongside EA1.

But to be fair, they are making big progress, from what I observed - its just… EA2 is so outdated by now, its not even worth using anymore. (I am currently using some Github build that is remotely “stable” regarding lumen.)

I think, at the moment, its best to just sit back and wait, if you have a stable build of ue5_main, since every build breaks something, fixes something, changes something.

Try this Cvar: “r.lumenscene.recaptureEveryFrame = 1” to Force SurfaceCache recapture every frame.
Notice :
Enable HardwareRaytrace, And Set “Default RHI” to DX12 in ProjectSetting.

There is my Lumen lighting resoult: HWRT + ReflectionQuality4 + “r.Lumen.Reflections.ScreenTraces = 0” + “r.lumenscene.recaptureEveryFrame = 1”
This in EA2 Version.
Hope these settings can improve your reflection :grinning:


Hi, the first part made the reflections black on the sphere. The DX12 was already turned on. I think that this might be due to the fact that I am using 1070 Ti which obviously is a non-RTX card. I will be making an upgrade to 3070 Ti in a week and I will check then if the problem will be still there.

recaptuerEveryFrame = 1 makes whole lumen scene black except direct lighting. So this won’t work for interior lit up mostly by GI

Oh! I tested it in my interior, and this Cvar really doesn’t work with GI.
I hadn’t noticed anything like this before,Sorry :sweat:

I think people should start to verify if the bugs still apply to the current github version, since the EA2 version is ancient by now - at least in terms of changes/differences to even a 4 week old build from Github.

Alternatively… Epic could provide EA3…

Not to be mean or anything, but how are people supposed to report bugs if the latest build they are using is 7 months old? Going by normal shedule, that would be two engine versions, and then something on top.

I already see it happen: Epic releases UE 5.0, and it is a mess, because so many people who rely on the non-github version couldnt check an updated version.

Just look at EA2 (left) vs. Github, from December (right) - its very different.


You’re my hero for posting a comparison screenshot between the two versions! :smiley:
I agree, Epic not posting any new EA, or Preview builds for UE5 in so long is going to cause both them and us a lot of stress… I hope they share a new build sooner, rather than later.
Especially because UE 5.0 early 2022 release target was confirmed in a recent Twitch stream.

About your screenshot: I think the Github December version looks noticeably better.
In particular the bushes on the ground look actually quite decent now.
Does lumen support translucency by now? What about SSS?

The tree canopies still look way too dark to me… did you do anything different than with the bushes?

Is this is a lumen bug? I am running UE5 EA 2.
This is just a default scene with a default sphere (and the color of the ramp is changed slightly). It also happens on an empty scene with just a light and a sphere.

I have also seen it on the terrain. Perhaps it is related to curved surfaces? I don’t think it happened in EA 1

This is the terminator problem and it has been in the engine for a decade at least

There are two kinds of shadows:

  1. Form shadows (“shading”)
  2. Cast shadows

Form shadows use the vertex normals of a mesh, which can be used to make a mesh appear “smooth” even when the geometry is actually extremely faceted.

Cast shadows don’t do that, they only consider the geometry of the mesh. So if you don’t have enough geometry then you end up with cast shadows in areas you don’t want them.

The solution is to use more geometry