Global illumination (GI) is the fastest way to discover that a PBR material is not actually PBR. Direct light can hide a too-dark albedo or a baked shadow in the color map. Bounced light multiplies those errors around the room. If your interior goes brown and muddy after you enable GI, fix the textures before you raise bounces or exposure.
Why GI is a texture test, not only a light test
In a path tracer, a bounce samples the albedo of whatever it hit. A dielectric floor at 20 sRGB reflects almost no energy. After two bounces the room is soot. A floor at 180 sRGB with a hidden gradient in the albedo tints every wall. That is energy transport, not a “GI bug.” The map rules in the PBR textures guide exist so GI stays stable.
Metalness complicates this: metals have no diffuse lobe, so they do not fill a room with colored bounce the way painted walls do. A chrome box will not light a set. Use dielectrics for bounce and metals for highlights.
Albedo ranges that survive GI
Keep dielectrics roughly in a 50–240 sRGB band (about 0.04–0.87 linear, depending on your color pipeline). Coal and soot sit lower on purpose. Fresh snow and white paint sit high but not at 255 on every channel. If a wood floor is a screenshot with contact shadows, GI will reprint those shadows on the ceiling.
- Check albedo in a flat, unlit view or a utility albedo AOV.
- Remove baked AO from color. Multiply AO only if you have no GI and need a cheap cavity.
- Grade saturation down if a red wall turns the whole GI solution pink.
Free CC0 maps from the Locker3d library are authored as lighting-free photoscans. Use them as a reference for luminance when a marketplace pack looks “rich” in a studio and filthy with GI.
Roughness, metals, and caustic-like noise
Very low roughness plus GI means sharp indirect highlights. That is correct and noisy. Raise samples or use a denoiser on the indirect specular, do not raise roughness just to quiet the render unless the surface is actually matte. Brushed metal should keep anisotropic or mid roughness so GI does not place a tiny sun in every scratch.
Match texture resolution to how large the surface is in GI: a 4K tile on a warehouse floor is wasted if the camera never sees it, but a too-small repeat can create a visible pattern in colored bounce. See the resolution guide.
Lookdev setup that predicts GI
Do not approve materials only under a single studio HDRI. Use IBL for reflections and a closed gray or white box with at least two GI bounces for interiors. Combine both: an HDRI through a window and GI inside. Practical HDRI steps are in HDRI and PBR lighting.
In Blender Cycles, check Clamp Direct/Indirect only after maps are sane; clamping hides fireflies and also hides energy problems. In Unreal, Lumen or path tracing will show the same albedo errors as Cycles, just faster.
A short GI-and-PBR checklist
- Albedo has no shadows, no AO, no specular blobs.
- Metalness is 0 or 1 except on tiny transition pixels.
- Roughness variation is in the map, not faked with extra lights.
- White furnace or gray-box test: a fully white environment should not make dielectrics brighter than the environment (energy conservation).
- Licenses: Locker3d is free CC0, so you can flatten an albedo that still has dirt you do not want. Details in CC0 can and cannot.
More render and material notes are on the blog. If GI looks wrong, believe the bounce: it is showing the albedo you actually shipped.
Frequently asked questions
Why do my PBR materials look fine in a studio HDRI but dirty with GI?
Global illumination multiplies albedo by bounced light. If albedo is too dark or contains baked AO, each bounce darkens the room. Fix albedo luminance and remove baked shadows before you raise GI intensity.
Should I bake AO into albedo when using GI?
No. GI already darkens crevices. Multiplying baked AO into albedo double-occludes and dirties color. Use AO as a separate cavity or leave it off in offline GI.
Do free CC0 textures work with path-traced GI?
Yes, if albedo is lighting-free and in a plausible range. Locker3d textures are free CC0 photoscans intended for PBR. Preview them in a gray box with GI before you trust a beauty shot.