Indirect Light Volumes: Probe-Based Global Illumination and Bounce Lighting

Indirect Light Volumes in s&box use a grid of probes to sample indirect light from all directions. When rendering, the system interpolates between nearby probes to shade each point — light bouncing off a red wall tints nearby surfaces, sunlight from a window fades naturally into a room.

Properties

• Probe Density — How tightly packed probes are. More probes = finer detail but higher cost. Crank up for tight spaces, keep low for open areas.
• Normal Bias — Pushes sample points away from surfaces. Increase if you see dark speckles or self-shadowing artifacts.
• Contrast — Makes bounces punchier. Higher values crush darks for a more dramatic look.
• Inside Geometry Behaviour — Whether to remove or relocate probes detected inside backfacing geometry.

Best Practices

• Position volumes to cover key areas without overlap
• Bake after major scene changes
• Use low density in open areas, add a second volume for detail in specific regions
• Use thicker wall geometry to prevent light leaks

Limitations

• Thin walls leak light — probe grid can't see walls thinner than probe spacing
• Not real-time — baking happens in editor only, no dynamic runtime updates. Re-bake for scene changes.