Why does Lumen produce different initial lighting results when reopening an Unreal Engine project?

FistOfFury1
Thu, 16 Apr 2026 14:55:33 +0000
Rendering

When I first import a Datasmith file into my UE5 scene, the result looks like Picture 1: the lighting, shadows, and AO are extremely rich and heavy, almost like a cinematic photograph. The scene has very clear depth information from occlusion, with foreground and background objects well-separated and ordered — it looks like an offline-rendered CG shot.

However, after closing and reopening the project, the thick, deep AO is frustratingly gone. Instead, I only get Lumen’s small-scale, weak AO. With the depth information lost, all models appear flat, messy, and the whole scene looks dull.

AI responses told me that Lumen automatically applies background optimizations after the initial load, and these changes are irreversible, making it impossible to fully restore the look I had right after importing. But I’m not sure if that’s accurate.

So I’m asking the community: how can I keep the scene’s lighting and occlusion permanently in that initial, just-imported state, even after closing and reopening the project?

6 posts - 3 participants