In this guide
When baked lighting shows seams, first confirm the mesh’s lightmap channel, UV layout and bake settings. Do not assume that good texture UVs are good lightmap UVs, or that raising resolution fixes every artifact. Establish whether the visible problem belongs to geometry, shading or the baked-lighting workflow.
Start by confirming the project actually uses lightmaps for the affected object. Dynamic lighting problems need a different diagnosis. Record the engine version, asset revision and exact scene in which the seam appears.
Inspect the channel used by the bake
Open the imported mesh and identify the channel selected for lightmapping. Then inspect that channel directly. A second UV channel existing in the file does not prove the importer or mesh settings use it.
Epic’s lightmap UV generation guide distinguishes source and destination channels and describes padding-related generation settings.1 Preserve those settings with the receiving record so another artist can reproduce the result.
| Observation | Check | Likely next action |
|---|---|---|
| Overlap in the selected bake channel | Islands and intended uniqueness | Correct the layout or generation input |
| Bleeding near island edges | Padding at the target resolution | Repack and rebake |
| Seam follows a geometry join | Boundary and shading continuity | Inspect source and assembled layout |
| Artifact only in one scene | Lighting and bake configuration | Reproduce with controlled settings |
Reproduce a small bake
Use one affected asset, a simple environment and a controlled light setup. Retain the original settings. Change one relevant variable, rebuild lighting and capture the same camera view. Keep the before-and-after files or settings record; an unrelated fresh scene does not explain why the original scene failed.
Generated UVs should be inspected, not treated as automatic acceptance. Check whether the input charts are suitable and whether the result has the required separation. If a layout issue persists, repair the source rather than repeatedly increasing resolution.
Keep budgets attached to the proposed fix
Resolution increases affect memory and build work. Ask whether the asset’s screen importance justifies the increase and whether the same artifact could be resolved with a better layout. Compare against neighboring modules under the same bake conditions.
The game asset budget guide helps record the resource decision. For repeated pieces, use the modular kit test so a local fix does not leave visible discontinuities across the assembled environment.
Separate lightmap acceptance from texture acceptance
Base-color tiling can be intentionally repeated; a lighting layout may need a different arrangement. Record the purpose of each UV channel and preserve the source export. If reimport changes channel order, revisit every receiving setting that refers to an index.
Download the lightmap diagnosis sheet, which leaves bake results and acceptance blank. Attach the actual bake observation to the exact export and importer configuration. Use the Rendora game workflow for source organization and available validation evidence; it does not substitute a browser preview for a target-engine lighting build.
Lightmap questions
Is a second channel always required?
Determine the lighting workflow and engine requirements first. Do not add channels merely to satisfy a generic checklist unrelated to the receiving project.
Why does the seam remain at higher resolution?
The cause may be the wrong channel, unsuitable layout, geometry or shading rather than insufficient pixel allocation. Diagnose in that order before spending more memory.
References
- Epic Games, Generating lightmap UVs, checked October 26, 2026.
About this guide
Rendora publishes practical guides for teams working with configurable 3D assets and traceable production handoffs. Updated October 26, 2026.