What is Global Illumination (GI)?

Global Illumination - Definition & Benefits

GI distinguishes direct light from indirect light; the latter is created by multiple reflections in the room. Without GI, renderings look flat; with GI, interior scenes, fabrics, wood and paint look credible. For consistent results, you need physically correct materials (→ PBR - Physically Based Rendering) and clean light sources/HDRIs (→ HDRI / Image-Based Lighting).

The PBRT standard work provides a clear explanation of the fundamentals of GI and path tracking - ideal for classifying light transport and BRDFs(Physically Based Rendering - pbrt.org).

How Global Illumination works (simply explained)

Light hits surfaces, is absorbed/scattered/reflected and illuminates other points (color transmission, soft shadows). In practice, this is calculated using Monte Carlo methods(path tracing, possibly bidirectional/MLT), photon techniques (photon mapping/SPPM) or radiosity (area-based).

The documentation Blender - Light Paths is a compact reference work for parameters and bounces in practice(Blender Manual: Light Paths).

Global Illumination in image comparison

Move the slider through four variants - Final, Direct, Indirect (GI) and Albedo Map - and see how indirect light bounces brighten the scene and transfer colors.

Real-time GI vs. offline GI (with clear recommendation)

GI workflow in 7 steps

1. CI-Mood & references (time of day, color temperature, subject lights).
2. Geometry & UVs: clean normal/UV islands avoid light artifacts (→ UV mapping).
3. Material setup (PBR): Albedo/Base Color without shadow; Roughness for gloss width; Normal for microrelief.
4. Light & HDRI: Base light via HDRI, set key/fill/accent motivated (→ HDRI / IBL).
5. GI sampling & denoiser: start sensibly (e.g. 64-256 spp), AOV-supported denoiser (albedo/normal) reduces rendering time.
6. Tone mapping & color space: uniform color space/ACES, values clamped, fireflies under control.
7. Delivery: Hero stills offline in your render engine, interactive variants via lightmap/probe; series production scaled via render farm.

Frequent GI errors in interior scenes - and quick fixes

• Flat rooms: too few bounces/HDRI too dark → bounce +1, check HDRI exposure & rotation, additional motivated area lights.
• "Milky" look: Albedo baked with light / wrong color space → Albedo as sRGB/Color, do not bake GI into textures; check PBR values.
• Splotches/banding: too hard caches/too few samples → increase min/max samples, denoiser with AOVs; oversample problem areas locally.
• Noisy corners: increase indirect samples; AO discreetly as contact accentuation (→ Ambient Occlusion).
• False gloss accents: Roughness/IOR implausible → use reference material + plausible IORs.

The famous Cornell Box clearly shows how color bleeding works and serves as a reference for GI tests(Cornell Program of Computer Graphics).

Methods & use: comparison of GI methods

FAQ - Global Illumination (GI)

How do I choose the right GI settings for interior vs. product release?

For interior scenes, 3-6 bounces, a good HDRI and clean PBR materials make sense - we show details in our projects for Interior room visualization. For cut-outs/packshots, fewer bounces + subtle AO are often sufficient; more on this at Clipping & packshots in 3D.

How do I speed up GI without any visible loss of quality?

Use denoising (with albedo/normal AOVs), portal lights/window areas, sensible clamp values and - for static sets - baked GI. For predictable output cycles and series, a clean pipeline structure like in our 3D Render Studio.

Which engines/tools deliver practical GI today?

For realtime: Lumen in Unreal (dynamic GI/reflections) and Progressive/Enlighten pipelines in Unity are robust options - see Unreal Engine: Lumen Global Illumination and Unity Manual: Global Illumination. For offline/design reviews, NVIDIA Omniverse provides a strong path tracing implementation(Docs: Omniverse - Path Tracing).

How do I keep CI colors stable despite GI?

Work with color-pure albedo, consistent tone mapping and references (color samples/charts). We ensure reliable material bases in the workflow - from scan to shader - in Digitize surfacesso that brand colors appear identical across all channels, even with GI.

GI in AR/VR: What is realistically possible?

In VR/360° tours, we often use baked GI (lightmaps/probes) for performance; we add interactive highlights dynamically. For web/showrooms, we link GI setups to high-performance viewers - see Virtual Reality & 360° Tour and the 3D viewer on the web.

When should I bake GI (lightmaps) and when should I calculate live?

Baking is worthwhile for large, static rooms (showroom, retail set, exhibition stand). Live GI (Lumen/SSGI) is ideal for configurators or dynamic cameras. Combinations are often best-of-both-worlds: basic GI baked, reflections/details live - perfect for product experiences on the web or in interactive brand spaces (cf. 3D product visualization for e-commerce).

Which denoisers work best for GI?

Modern renderers provide integrated denoisers; a popular example is Intel Open Image Denoise (documentation: Intel® Open Image Denoise). Important: Feed the denoiser with AOV auxiliary passes (Albedo/Normal) and only reduce the indirect noise so that edges/highlights remain crisp.

How does GI influence render times for animations - and what can I do?

Temporal denoise, GI caches (stable prepasses), smooth camera paths and hybrid playout (hero frames offline, fill frames optimized) help with animation shots. For campaign videos, we plan the output early on - more on this in 3D animation & product video.