What you're seeing
Baked lighting shows dark seams, light leaks, or shadow color bleeding along UV chart boundaries.
Likely causes
- Lightmap UV charts do not have enough padding.
- The mesh uses the wrong Lightmap Coordinate Index.
- The effective Lightmap Resolution is below the Min Lightmap Resolution used to pack generated UVs.
- Fragmented charts or poor UV coverage leave too little texel area for stable lighting.
Check in this order
- 01Use Lighting Only to confirm that the seam belongs to the baked lighting result.
- 02Inspect the assigned Lightmap Coordinate Index and its UV overlay in the Static Mesh Editor.
- 03Compare the mesh or instance Lightmap Resolution with the Min Lightmap Resolution used to generate its UVs.
- 04Use Lightmap Density to correct inconsistent texel density, then rebuild lighting.
Views and commands
Lighting Only
View Mode > Lighting OnlyRemoves material texture detail so the baked-lighting result can be inspected.
Lightmap Density
Alt+0Shows lightmap texel density relative to the configured ideal and maximum.
Static Mesh setting
General Settings > Lightmap Coordinate IndexSelects which UV channel Lightmass uses for the mesh.
Static Mesh setting
General Settings > Lightmap ResolutionSets the default baked lightmap resolution for mesh instances.