Why does Lumen screen tracing band on smooth surfaces?

Step count too low for the surface roughness. Raise r.Lumen.ScreenProbeGather.ScreenTraces.NumSteps. Or limit screen tracing to rougher surfaces via TraceMaxRoughness console var.

r.Lumen.ScreenProbeGather.ScreenTraces.NumSteps default 12; raise to 24 for cleaner. r.Lumen.ScreenProbeGather.IrradianceFormat 1 for HDR cache.

On supported GPUs, Lumen Hardware RT bypasses screen-trace artifacts. r.Lumen.HardwareRayTracing 1.

Fix: Lumen Screen Traces Banding Smooth Surfaces

Quick answer: r.Lumen.ScreenProbeGather.ScreenTraces.NumSteps 24. Or enable Hardware RT.

Glossy floor reflects with visible bands. Screen tracing's step count too coarse for low-roughness reflections.

The Fix

Console (or DefaultEngine.ini):
r.Lumen.ScreenProbeGather.ScreenTraces.NumSteps      24
r.Lumen.ScreenProbeGather.ScreenTraces.MaxRoughness  0.6
r.Lumen.HardwareRayTracing                            1      // if GPU supports

PostProcessVolume:
  Lumen Reflection Quality:                          2

More steps + Hardware RT = clean reflections. MaxRoughness scopes screen tracing to mid-rough surfaces; mirrors fall back to surface cache or hardware.

Verifying

Glossy floor reflects clean. Bands gone. GPU profile: ms slightly up but acceptable for the visual gain.

“More steps. Hardware RT. Reflections clean.”

Related Issues

For Lumen software glitches, see software. For TAA ghost, see TAA.

More steps. Bands fade.