Why does Lumen software ray tracing show light glitches?

Software tracing uses Distance Fields and Mesh Cards; coarse data leads to leakage and noise. Switch to Hardware Ray Tracing if GPU supports, or raise Software Tracing Quality + Mesh Distance Field Resolution.

How to enable Hardware Ray Tracing?

Project Settings → Rendering → Use Hardware Ray Tracing when available + Support Hardware Ray Tracing. RTX or RDNA2+ GPU required.

r.Lumen.ScreenProbeGather.RadianceCache.NumProbes higher = cleaner. r.Lumen.ScreenProbeGather.IrradianceFormat 1 = full HDR cache.

Fix: Lumen Software Tracing Produces Glitches

Quick answer: Use Hardware Ray Tracing where supported. Software path: raise Software Tracing Quality and per-mesh DF resolution.

Indoor scene with Lumen GI. Visible light leaks through walls. Software tracing samples coarse Distance Fields.

The Fix

Project Settings → Rendering:
  Use Hardware Ray Tracing when available:    true
  Lumen Hardware RT Mode:                     true
  Software Tracing Quality:                   High
  Generate Mesh Distance Fields:              true

Static Mesh assets:
  Distance Field Resolution Scale:            8

Hardware RT removes most glitches. Software path with high quality + per-mesh DF resolution is the fallback for non-RT GPUs.

Verifying

Light leaks reduced. Lumen Visualization shows clean DF coverage. GPU profile: hardware RT cost vs software trade-off.

“Hardware RT or higher quality. Glitches fade.”

Related Issues

For TAA ghost, see TAA. For mobile shader precision, see mobile.

Hardware RT. Glitches gone.