Some of this information was covered above. There are ways to help alleviate and reduce this.
I’m going to be a little redundant here but just to make sure that a lot of the information is condensed into a single post.
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Make sure you have a second UV setup specifically for your Lightmap.
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(This is for modular hard edges like walls) Set up your grid spacing in your UV and snap the vertices to them.
- Target a LM Resolution (If you target 64 you can adjust higher via power of two and you will not have to manually target each LM specifically)
- Use the following formula to get the grid spacing for your UV: 1 / [LM Resolution] = Grid Spacing ie. 1 / 128 = 0.0078125
- any edge that is not snapped along a grid line can be shadowed. This is why there will sometimes be jaggies or artifacts with the shadows
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For modular walls, the recommended workflow to not have seams is to have other meshes that cover this area or to have your edges meet at corners.
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If not your workflow, you can reduce the edge seams by doing the following. Some of these settings WILL increase light build times.
- Place a lightmass importance volume in your scene covering your playable area.
- Under World Settings you can adjust the following:
-Indirect Lighting Quality 2 or higher should work (may need to be higher up to 4 but will increase light build times)
-Indirect Lighting Smoothness to 0.6.
-(Optional) Environment Color - change to anything other than full BLACK. This will lighten your shadows and increasing it just a little in the grey side will help sometimes.
If this isn’t working for you the last option is to adjust Static Lighting Level Scale under World Settings. Default is 1.0. If you adjust this lower you can get better results. This will significantly increase light build times in some cases. This is the scale which light is build. Default is the current UE4 scale of 1 unreal unit = 1cm.
Using these methods should help in going a long way to get the results you’re looking for.
Feel free to ask any questions you may have. 