UE 5.1/5.2 issues with baked lighting

[Samleybrize]

Hello,

In 5.1 and 5.2, when I build lighting (with any quality) I can clearly see a noticeable seam/transition between meshes, but only with lights with indirect lighting. In 5.0 it works as expected. I turned off Lumen and virtual shadow maps.

Example scene with only a point light with “Indirect Lighting Intensity” = 1.0 (with 3 cubes next to each other)

And with “Indirect Lighting Intensity” = 0.0

Is there any setting that I need to tweak?

[Arkiras]

This has always been an issue with CPU lightmass in Unreal, since before UE4 probably. Lightmass processes each mesh on a different thread, and they don’t know what the other threads are doing.

There are two main solutions to this:

1. Merge your meshes together or redesign them when necessary so that you can hide seams in places they won’t be noticeable
2. Use higher quality lightmass settings.

Both of these are likely to result in longer build times, but the latter especially.

For reference, here’s a comparison I did a while back of different lightmass settings and their effect on quality and build times:

Another option is to simply use GPU lightmass instead, as it doesn’t suffer from this issue. You may encounter some other issues though, as GPU lightmass has different limitations.