Why Am I Getting Lighting Artifacts and Incorrect Shadows After Building Lighting in Unreal Engine 5?

Development Rendering
1

Hi everyone,

I’m currently working on an environment project in Unreal Engine 5.3 using Lumen for dynamic lighting. However, after building the lighting (even though Lumen doesn’t require it), I’m seeing strange artifacts and inconsistencies in shadows—especially in interior spaces lit by skylights and emissive materials.

Here are some details about the issue:

  • Artifacts: Weird blotchy shadows on walls and floors, even in well-lit areas.
  • Incorrect Shadows: Shadows sometimes appear offset, too soft, or missing entirely.
  • Setup: I’m using Nanite meshes, virtual shadow maps, and all lights are set to dynamic or movable.
  • Tried Fixes: Cleared and rebuilt lighting, adjusted shadow bias settings, disabled static lighting entirely, and experimented with different lightmass settings (even though I’m using Lumen).

I’m a bit confused because I thought Lumen handled most of this in real-time, and didn’t rely on light baking. Is it possible that some remnants of static lighting or incorrect settings are causing conflicts?

My questions:

  1. What’s the best practice for setting up lighting in UE5 when using Lumen exclusively?
  2. Should I completely disable static lighting and light building when using Lumen?
  3. Has anyone else encountered artifacts like this—are they engine-related or more likely due to level setup?

Any tips, clarification, or examples of correct setups would be super helpful. Thanks in advance!

2

Hi there @Daniel_Halle,

You are correct that Lumen does not support built lighting. In all honesty, I’m kinda surprised it even let you attempt a build. Either way, when you actually attempt to package your game, Lumen should throw out all of your lightmaps and leave you with an unbuilt scene.

Based on the setup you are describing, it seems as if you’ve tailored your scene towards next-gen tooling, and thus I would recommend sticking with Lumen and to not continue baking your lights. Nanite and Virtual Shadow maps are meant to work in tandem with Lumen, and having all of your lights set to Stationary/Moveable is also Lumen-tailored. Just a side note too, with Lumen enabled, Stationary lights don’t actually do anything, since their original setup was for to allow for baked lighting with some variability at runtime. I suppose there’s no harm in keeping them stationary, just know that you’re not gaining anything from it.

If you’re looking for the more realistic lighting that baking provides, unfortunately Lumen has its limits. You can increase the number of Lumen probes and bounces (basically determining how much bounce lighting there is) but this will be at the cost of performance. Lumen does open up a postprocess setting called “Skylight Leaking”, which you can use to cheat some really nice ambient lighting into your interiors.

All of that being said, just so you know for the future, there are a lot of settings for light baking that can cause errors. These can range from poor light map UVs, bad lightmap resolutions, or an undesirable amount of light bounces. Luckily for you, unless you’re trying to create a game optimized for mobile or previous-gen consoles, light baking in Unreal is mostly a thing of the past due to the massive time sink.

Here is the official documentation for a full technical breakdown of Lumen. I would highly recommend you at least skim this, so when you encounter errors in the future, you know how to detect and fix them.

This page is also a great resource for understanding the basics of Lumen’s quality vs speed controls. There are additional adjustable Lumen cvars, but for now, this should cover everything you need.