We’re exploring an issue with Lumen GI in locations like tunnels and bigger darker interiors.
When entering interiors Lumen scene is noisy and updates very slow, in dark interiors there are a lot of artefact caused by the high lighting intensity, fog also appears to catch these values and looks brighter than the scene intensity. The slow update is more noticeable when entering the ‘’interior’’ with a fast moving camera. The options in the Post Processing Volume Lumen GI settings are not helping, also sky leaking isn’t an option as it adds high intensity and makes the local lights not visible, but also flattened the scene.
Lighting is set close to PBR values with average EV 12 (exterior). Sun intensity is 22K, skylight/HDRi reads from the sky atmosphere illuminance. Lumen is using default settings, no ray tracing. Geometry is split to pieces and Nanite. UE 5.5
There is a post processing volume in the tunnel just to reduce the bloom and lens flare. Fog is off in most of the videos but the one in the entrance to show case the GI leak in the volumetric fog.
Video: Tunnel_PBR_01 it’s a 180m long tunnel with moving camera.
Tunnel_PBR_01.mkv (25.4 MB)
Video: Tunnel_PBR_03 – same tunnel but faster moving camera where we can see the slow GI update.
Tunnel_PBR_03.mkv (17.4 MB)
Video: Tunnel_PBR_02 – it’s very long tunnel, end of the geometry is outside of the GDF range.
Tunnel_PBR_02.mkv (14.3 MB)
Video: Entrance_PBR_01a – 100 m long tunnel with a curve is going to same size room, high contrast on the entrance, them splotchy artefacts before the GI slowly update and fade to black, the noise is moving based on the camera position.
Enrance_PBR_01a.mkv (13.7 MB)
Enrance_Fog_PBR_02 – same interior but with the fog ON.
Enrance_Fog_PBR_02.mkv (11.8 MB)
We did try with very low (non PBR) values and GI looks stable no artifacts (or at least not visible), Sun intensity is set to 160 Lux, average EV 4.5 (exterior).
Video: Tunnel_nonPBR_01 – no artefacts.
Tunnel_nonPBR_01.mkv (12.9 MB)
How we can improve Lumen to cooperate with sun/sky PBR values, without these visual artefacts?