Unreal Engine 5.8 NEW Lumen Probe Occlusion

Summary of Technological Concepts / Features

• New Unreal Engine 5.8 Lumen feature: The video discusses Lumen medium-quality global illumination using “iridescent fields with probe occlusion” (exact naming may be slightly off due to auto-subtitles).

• Probe-based GI approach: The feature is described as Lumen “probe-based GI”, conceptually similar to NVIDIA RTXGI, where GI probes are used to determine lighting.

• Performance claim (Epic): It’s claimed to run ~2× faster than Lumen high quality, with an example of ~60 FPS on PS5 for the comparison baseline.

Guide / Tutorial Steps (Console Commands + Setup)

1. Use UE 5.8 (preview or launcher version).

2. No project/editor toggle yet: The narrator indicates there are currently no project settings or editor settings to enable this feature.

3. Enable via scalability / GI quality:

   • Set Viewport Scalability → Global Illumination = Medium, or
   • Use a console command: set global illumination quality to 1 (subtitles indicate mapping: 0=Low, 1=Medium, 2=High, 3=Epic)

4. Visualize the probes:

   • Uses a command like: Lumen irradiance cache visualize 1 to show probe placement.
   • Result: many small GI probe points appear in the scene.

Key Behavior Differences: Lumen Probe Occlusion vs RTXGI

• Auto-placement based on scene meshes (Lumen):

  • Probes are spawned around objects placed in the level (e.g., meshes/islands).
  • If an object is duplicated, probes spawn around the new instance as well.
  • No manually authored probe volumes are described for this workflow.

• RTXGI requires volumes (as described by the narrator):

  • RTXGI uses probe volumes that you place and scale to control coverage.

• Important limitation:

  • The narrator states the auto-probe spawning behavior works only for the Medium GI setting.

Runtime / Visualization Observations

• When running the level, probes appear to be generated around the character at runtime:
  • Approximately ~12–18 probes around the player character (as described).
• The narrator infers there may be some caching/static behavior associated with the Medium preset.

Tuning / Developer Controls Mentioned

• The narrator notes there are many console commands, but:
  • No documentation is available yet
  • They are not fully familiar with parameter details
• One parameter/command mentioned:
  • Probe resolution starting value shown as 16, with a possibility to increase.
• Mentions likely tunables (e.g., spacing) but does not confirm exact specifics.

Performance Testing Plan (Mentioned)

• The narrator says they still need to run real performance tests comparing:
  • Lumen High Quality vs Lumen Medium (probe occlusion)
  • Possibly on Steam Deck, after packaging a demo
• Expectations:
  • Medium/probe occlusion should perform better
  • They will also compare GI visual quality

Sources / Main Speakers

• Primary speaker: the YouTube channel narrator (“Hello guys, welcome back…”).
• Secondary referenced source: Epic (for the performance claim and feature description).