Hi all,
This is my first post here, I tried to search about my issue but didn’t find the answer yet.
I’m recreating the church of the light by Tadao Ando and I have a strange issue with material on the wall. In the following screen shot, you can see the top part of the wall is different from the bottom part. It is two separated object but they have the exact same material.
Both objects are manifold, don’t have overlapping uvs and normals are pointing in the same direction (outside)… So I don’t really know what is going on ?
If you have any clue about what I am doing wrong, that would be nice !
Thanks a lot ! 
That’s an issue with the lightmap, the meshes are processed individually and there can be differences in the lighting between objects, there’s some things you can do to improve it, but ultimately the solution is to not build surfaces like that out of multiple objects
Woah that was fast !
Thanks a lot for your answer DarthViper107, I’ll join these objects then.
Thanks again !
As Darthviper suggests, ideally these would be better as a single object rather than multiple.
You can open the World Setting > Lightmass tab > adjust Indirect Lighting Quality (2 or higher, also will increase build times) and Indirect lighting Smoothness (~0.75 - 0.6 should work). This will help reduce the shading differences, but not necessarily all of them.
You can also have a look at this thread that goes more into detail about this and working with the lightmap UV to help reduce the issue. Modular Asset Lighting Problem - Rendering - Epic Developer Community Forums
This is caused by the indirect lighting bounce create using lightmass. This is a topic that Eric and I want to get up on our Wiki Lighting Troubleshooting guide(linked below in my signature) soon. Just haven’t had the necessary time lately to finalize and get it up on the Wiki.
Thanks Tim for your detailled answer. That’s some useful reading material to know!
