Global Illumination
Light bouncing between surfaces
Also known as: GI · Indirect lighting · Bounce light · Radiosity
Definition
Global illumination (GI) is the simulation of light that bounces from surface to surface, so a red wall tints the floor beside it and a sunlit room lights its dark corners. It is what makes a scene look natural instead of flat, because direct lights alone leave shadows pitch black. Games get it from baked lightmaps, light probes or real-time systems such as Unreal Engine 5's Lumen.
In production
Artists influence GI through surface color, emissive materials and the geometry of the scene: a bright albedo bounces more light, and saturated walls tint everything near them. Avoid pure white and pure black in base color so bounce stays believable. Thin walls and gaps cause light leaks, and baked GI needs clean lightmap UVs, so check both when lighting looks wrong.
Tools that use Global Illumination
See also
Lumen
UE5 dynamic global illumination
Lightmap
Pre-baked indirect lighting
Lightmap UV
Second UV channel for baked lighting
Light Leaks
Light showing through walls and corners
Reflection Probe
Pre-captured cubemap for local reflections
Ambient Occlusion
Soft contact shadows
Emissive Map
Texture for glowing surfaces
Light Probe
Baked light sampled for moving objects
Baked vs Realtime Lighting
Precomputed or calculated every frame
Ray Tracing
Simulating light by tracing rays
Path Tracing
Physically accurate light with random sampling
Light Types
Directional, point, spot and area lights
Physical Light Units
Lux, lumens, candela and nits