Lumen GI and reflections

Select quality by target

• High-quality Lumen is the modern dynamic GI/reflection path for capable targets.
• UE 5.8 Lumen Lite is Beta. Medium GI quality (sg.GlobalIlluminationQuality 1) selects its Irradiance Field Final Gather (r.Lumen.FinalGatherMethod 0) for faster, lower-quality GI.
• Medium reflection quality (sg.ReflectionQuality 1) disables Lumen Reflections, uses SSR on smooth surfaces, and retains rough specular from Lumen GI.
• Below Lumen, use the project/platform's supported baked or simpler GI/reflection fallback.

Start from Epic's BaseScalability.ini and platform device profiles; they coordinate many interdependent settings to preserve a reasonably consistent look.

Isolate cost

1. Confirm Lumen passes are material in profilegpu/GPU trace.
2. Capture Lumen visualization/overview modes to find scene representation, update, reflection, or screen-trace problems.
3. A/B GI and reflection scalability independently.
4. Test worst-case dynamic lights, camera motion, emissive content, interiors/exteriors, and distance.
5. Validate temporal stability and lighting continuity on every tier.

Lumen uses async compute on supported consoles and can overlap other work. Per-pass timings can include overlap. Disable Lumen async compute only for isolated profiling, then restore it and judge total frame time; overlap is part of the shipping performance strategy.