Design Nomenclature / Light & Optics
Global illumination
Also called GI, indirect illumination
This entry has not been translated yet and is shown in English.
Any solution to light transport accounting for light that arrives after reflecting off other surfaces, not only direct from emitters. It is a category, not an algorithm — radiosity, photon mapping, path tracing, and irradiance caching all compute it, with different biases and different failure modes.
In practice
GI on a render toolbar means one specific engine setting. The term itself promises nothing about method, accuracy, or which light paths are actually included.
Not to be confused with
- RadiosityStrictly, a finite-element method that divides a scene into patches, computes form factors between them, and solves the resulting linear system for diffuse interreflection — view-independent, no speculars, and effectively unused since the 1990s. Loosely, and confusingly, the same word gets thrown at global illumination in general.
- Ambient lightIn a renderer, a constant added to every shaded point regardless of direction, occlusion, or distance — a flat lift with no physical referent, invented to fake indirect light before global illumination was affordable. In a room, the same phrase means the real diffuse light arriving from every direction at once.
- Ambient occlusionThe fraction of the hemisphere above a point blocked by nearby geometry — a purely geometric visibility term, no light involved. As a material channel it attenuates ambient diffuse in creases. Physically it is a coarse stand-in for the interreflection a GI solver computes properly, so under real GI it double-darkens.
- Path tracingMonte Carlo integration of the rendering equation: follow a random walk from the camera, sampling one scattering direction per bounce, and average many such paths per pixel. Unbiased — noise falls as the square root of the sample count and the estimate converges on the correct answer.