At specific distances from a thin wall, surfaces inside of a sealed chamber can receive indirect lighting from outside, leaking light into the chamber.
This appears to be due to how SWRT handles sampling the nearest Lumen Card, as it will sometimes sample the card on the other side of the wall from the interior mesh.
1. Download the Licensee's test project and generate project files (see addl info URL)
This test project is intended for 5.5. The following step is intended for testing on 5.7.
2. In "CornellBox_5_5.Target.cs" and "CornellBox_5_5Editor.Target.cs", change the DefaultBuildSettings and IncludeOrderVersion to the respective "Latest".
3. Compile the editor and open the test project.
4. Observe the cube "Cube3" inside of the sealed room, and how it appears to be casting light on the wall.
5. With location snap enabled and set to 10, move the cube towards or away from the wall by 10 units.
6. Observe the light leak ceases.
7. Restore the cube's location and repeat step 5 and 6 in the other direction.
8. Restore the cube's location (so that it is leaking light)
9. Find and open the shader "\Engine\Shaders\Private\DistanceField\GlobalDistanceFieldObjectGrid.ush"
10. Change the value of "DISTANCE_FIELD_OBJECT_GRID_CARD_INTERPOLATION_RANGE_IN_VOXELS" to "2.0f"
11. Execute the console command "recompileshaders changed"
12. Observe the light leak ceases
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-360404 in the post.
| 0 |
| Component | UE - Graphics Features |
|---|---|
| Affects Versions | 5.5, 5.7 |
| Created | Jan 12, 2026 |
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| Updated | Jan 12, 2026 |