UE5.6 Static Lightmap Artifacts

We are testing out a mixed-modularity workflow with static lightmapping. This set up doesn’t yet use H/ISMs, but just a first step in testing with regular StaticMesh actors. However, even with a simple scene, there are artifacts showing from the baked results. As called out in the screenshot, primarily seeing value differences in results across cubes, and a small gap in the sphere’s shadow silhouette.

Attached image shows 9 Maya static cubes with UV1 (respecting pixel boundaries), static directional light. I also tried the bake with both 64 andd 128px resolutions (and density viewmode confirms that is in the green) and saw no meaningful improvements. Please advise if this is a set up issue or a lightmapping limitation. Thanks!

Steps to Reproduce

Vanilla UE5.6

  • Project Settings
    • Enable Static Lighting
    • Disable Lumen GI and Reflection
    • GPU Lightmass never enabled
  • New Level
    • No WorldPartition (for now)
  • Mesh
  • Static
  • Has UV1
    • Disable Nanite
    • One static directional light
    • Bake Production Quality

Hey Joe,

Sorry for the late reply. Our lightmap experts unfortunately no longer works at Epic but as far as my understanding goes both artifacts are known limitations of per-actor static lightmapping, not setup errors. Each actor’s lightmap is solved independently — no cross-mesh continuity. For shadow gap, it’s a combination of shadow bias and any non-zero Source Angle penumbra at contact points. You could push geometry to overlap slightly and check Source Angle. Resolution increases won’t help either issue but once H/ISMs enter the picture, lightmap atlasing behavior changes and some of these seam issues may behave differently.