Lumen
UE5 dynamic global illumination
Definition
Lumen is Unreal Engine 5's real-time global illumination and reflection system. It computes indirect lighting and reflections dynamically — moving a light source updates bounce lighting and mirrored reflections immediately, without baking. Lumen replaces UE4's lightmass workflow for most projects and is what gives recent UE5 titles their cinematic look.
In production
Lumen has performance implications — most console UE5 titles run it at 1080p or lower internal resolution with software ray tracing and rely on temporal upscalers (DLSS, FSR, or UE5's own TSR) to reconstruct a 4K output image. Hardware ray tracing improves quality but tanks framerate without a high-end GPU, which is why most shipped console titles default to Lumen's software ray tracing mode rather than hardware RT. Lumen's Global Illumination and Reflections are toggled as separate settings in the Post Process Volume, each with its own quality tiers that trade ray count and probe resolution for performance. A common production issue is "Lumen ghosting" — smeared, delayed lighting response visible when a bright light source moves quickly, caused by the temporal accumulation Lumen relies on to denoise its lower ray counts.
Learn Lumen in
Tools that use Lumen
See also
HDRI
High Dynamic Range Image lighting
Nanite
UE5 virtualized geometry
Global Illumination
Light bouncing between surfaces
Virtual Shadow Maps
High-resolution shadows in Unreal Engine 5
Light Leaks
Light showing through walls and corners
Ray Tracing
Simulating light by tracing rays
Height Fog
Fog that is denser near the ground
Sky Atmosphere
Physically based sky and sunlight