Just getting started - reflection shimmering or blotchiness on arm of Minimal_Default map chair?

[ThisIsPequod]

I hope I posted this in the correct forum…

I’m just getting started learning UE5, taking a Udemy course, and it has me load up the starter content Minimal_Default map and save it as my own project, and I notice on some of the surfaces, like the arm of the chairs, the reflection seems to shimmer or is blotchy when I view it from certain angles, even when I’m not moving around.

It’s kind of hard to describe, but I can definitely see it at certain angles, and it happens in both the normal edit mode and the “play the level” mode. I’m not making any changes to the lighting, moving around, or anything like that. Just looking at the chairs from certain angles and I see that blotchiness moving around. I can also see a very slight cycling in overall brightness, like the overall image will get slightly brighter, then dimmer, and keep going up and down, just very slightly.

It seems to stop when I give focus to another program (like a browser) then starts up again when I focus back to the UE5 editor. Almost like when the editor has focus, it’s trying to constantly recalculate lighting or reflections or something.

This is a new rig, and I’m running latest updates for Windows 11, Nvidia 4090 driver, UE5, etc. So whatever it is shouldn’t be related to out of date drivers or anything.

There are so many options in UE5 I don’t even know where to look to start adjusting stuff. When I created the project, I did select raytracing, in case that’s relevant.

This isn’t something that would affect my going through the course, but it’s just distracting enough I’d like to know what’s causing it, and how to fix it. Does this sound like a problem other people have seen and have a fix for?

Thanks for any help anybody can provide!

EDIT: I also tried creating a second project with raytracing disabled, and I still see the same problem.

[jblackwell]

@ThisIsPequod

Almost like when the editor has focus, it’s trying to constantly recalculate lighting or reflections or something.

Yep, that sounds like UE’s GI and reflections system, lumen. We have a feedback thread for it, and it’s one of the most complex systems in UE’s rendering stack.

Basically, it’s tuned to hit current-gen consoles, so it makes a bunch of compromises to be performant, which cause noisy reflections and flickering GI. GI can be fixed just by cranking the quality settings, but reflections can’t really be rendered noise-free even with maximum quality (currently). You can remove the noise, but it will also remove a level of light from reflections.

TL;DR: it’s not a bug, it’s a limitation of unreal engine’s real-time GI and reflections.

[ThisIsPequod]

Thanks for that info! I found the Dynamic Global Illumination Method setting for the project, and changed it from Lumen to None, and I did see the problem go away.

I’ll chalk it up to Lumen still being a work-in-progress, and not my system being misconfigured somehow or me messing something up and all my projects were going to look bad.

Thanks again!

[jblackwell]

Essentially, yes. Lumen has had 4+ releases to bake, and while 85% works great, it really struggles with reflections on rougher surfaces (all real time solutions generally do). I’ll try to find it, but there’s a CVar that can improve noise quite a bit, need to recall what it is tho.