Building Lighting will Generate Additional Lightmaps after Rotating Lightsource

Lightmap sizes seem inconsistent after rotating a light source and rebuilding the lighting. This causes concern about file sizes when packaging the project that is using baked static lighting.

The licensee is reporting their lightmaps are generating two times the amount of lightmaps after rotating a light source in their scene. One of their engineers edited a coupe lines of code to fix the issue on their end.

I have added some screenshots to show the differences between building lighting as well as the fix the licensees would like to implement.

Tested in main 4.9 - 2607310
Tested in binary 4.8.1 - 2591939

1. Create new blank project without starter content.
2. In the empty level, drag some basic shapes into the scene.
3. Open the 'World Settings' tab and check the 'Force No Precomputed Lighting' to clear the lightmaps from the level.

Note You will need to build the lighting a few times for the number of lightmaps to reach zero. This seems irregular and possibly related.

4. Once the Lightmaps are clear, rotate your directional light source and uncheck the 'Force No Precomputed Lighting' and rebuild the lighting.
5. Rotate the light source one more time and rebuild the lighting.

Outcome: The number of lightmaps increases in size after rotating the light source and rebuilding the lighting. It only happens after the first rotation and does not continue to increase.

Expected: After rotating the light source, the lightmaps do not change in size until adding other objects to the scene.