How can I fix this UE5 interior light bleeding issue?

I’m having an issue with light bleed in interiors of buildings that seemingly disappears as I get closer to the area and reappears when I move further away. [Edit] This issue existed prior to upgrading the project to UE5 so I don’t believe this is a UE5/Lumen issue.

Project Details:

  • Lumen is enabled
  • Moveable directional light
  • No light source within the building
  • [Edit] All roofs/walls/etc. are separate, solid meshes.
  • [Edit] Walls/roofs/etc. are 20 cm thick

What We’ve Tried:

  • Adjusting shadow bias (Setting shadow bias to 0 fixes the light bleed, but causes artifacts to appear elsewhere in the world)
  • Adjusting shadow filter sharpness
  • Adjusting dynamic shadow distance
  • Adjusting cascade shadows and contact shadows
  • [Edit] A boxed light blocker around the building has zero effect
  • [Edit] Adjusting Lumen Scene Detail and Max Trace Distance on post process settings has no effect

Below are screenshots from a distance and in close-proximity to the far corner seen in the distant image.

Any help would be greatly appreciated! Thanks in advance.

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  1. Are walls are too thin?

Walls should be no thinner than 10 centimeters (cm) to avoid light leaking.

  1. Light Leaking in Large Cave-like Areas

In cave-like, or enclosed areas, if light leaking is happening, it is because Lumen limits how far rays are traced to improve performance, but missing an occluder causes light leaking.
In the Post Process Setting, raise the Lumen Scene Detail and the Max Trace Distance.

Thanks for the suggestions!

Our walls are 20 cm thick and when we adjust the Lumen Scene Detail/Max Trace Distance on our post processor absolutely nothing happens.

Any other thoughts?

Did you guys ever figure it out? I have the exact same issue and no solution in this thread works.

Try changing shadow slope bias in Directional light (also maybe Shadow resolution scale), you can also try changing Shadow bias but be warned setting it too low causes some strange lines to appear on objects.

We adjusted pretty much every lighting setting we have and seemingly had it fixed for a week or so, but now it’s back. Wish I had a definitive answer for you, but it seems like it’s just tweaking every little thing until it looks decent.

I had a similar issue today, I found that making the light blocker mesh around my room have solid 10cm thick walls fixed the issue (it wasn’t working to block light when it was a simple outer shell).

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I fixed the same issue in my scene by going into my Direct Light/Advanced/Shadow Bias.
It was set to 0.5. I changed it to zero and the leaking disappeared.


If you create a box as a light blocker, try to invert the normals. Saver is maybe to create a thick shell as a blocker box. Unfortunately not very handy.

I fixed a similar issue by changing the shadow setting in project settings/rendering from virtual shadow map(beta) to shadow map

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I fixed the same issue in a different way, I am posting it here because it may be helpful.

I “coated” the building using another mesh and that blocked the bleeding, as follows.

In my case, I was able to rectify this issue by setting Shadow Slope Bias to zero and maxing out Contact Shadow Length in the Directional Light; hopefully this helps someone that happens across this thread.

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