Lumen Noisy GI

I just started a blank project in UE5.0 Preview (5.0.0-19044958+++UE5+Release-5.0), and imported some simple geometry to test out Lumen GI.

I didn’t modify the sample game scene in any way, except for adding my geometry.

I’m noticing that on the interior, any shadowy areas where Lumen GI is rendered, it appears very noisy. I have tried switching between HW and SW Raytracing, but that doesn’t make any difference. I have also tried maxing out the Lumen quality settings, but that doesn’t make a difference either. Here’s a picture of what I mean:

Does anyone have an idea what’s causing this noise, and how I can get rid of it?


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If there’s no difference at all between SW and HW ray-tracing, I’ve normally found that means it’s disabled somewhere else in the project settings. A lot of the quality levers are also dependant on HWRT from my testing.

  1. Make sure your default RHI is Directx12, target platform Directx12 (I think they changed the language a little bit but that’s generally what got me in the past. You can have HWRT enabled, but it won’t do anything without this setting.

  2. Make sure ‘Support hardware raytracing’ is ticked on.

  3. Make sure ‘Use hardware raytracing when available’ is ticked on.

In all honesty though, that looks more like a shadowing problem than a lumen problem, at least for the direct shadows. Look at your virtual shadowmap settings and increase the Samples per pixel (I forget the CVar off the top of my head). If using RT shadows, similarly boost the sample count and you should be fine.

Important question: is the geometry all one mesh? Because if so, Lumen won’t work well. The card system the surface cache depends on does best when geometry is in as many small pieces as possible.

As for indirect shadows, I have the exact same problem: even with settings cranked to the absolute max, indirect shadowing still resolves with a lot of noise, when when there’s room in the performance envelope to boost it higher. I also haven’t figured out how to boost the quality through CVars, since I can’t figure out if indirect shadowing is classified as bounced lighting, shadowing, or a subset of AO.

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