# Irradiance probe volume

baked diffuse GI colour-bleed onto a moving object.

```{raw} html
<a class="example-run-button" href="../demos/features_3d_probe_volume.html">▶ Run in browser</a>

```

**Tags:** `3d` `gi` `irradiance-volume` `probe` `colour-bleed` `pbr`

An IrradianceVolume3D (design D10) bakes a grid of diffuse-lighting probes from
the scene, each storing the incoming radiance as spherical-harmonic L1
coefficients. A neutral sphere gliding through the volume trilinearly blends the
eight probes around it and evaluates their SH for each surface normal, so it
picks up soft indirect light baked from the surrounding walls: reddish as it
nears the red wall, greenish near the green wall, with a smooth wash in between.
Unlike screen-space GI this needs no on-screen source and survives off-screen
geometry, and unlike a reflection probe it is a low-frequency DIFFUSE term that
reads correctly on rough, matte surfaces.

The grid bakes once over the first few frames (``update_budget`` probes/frame),
then lights every subsequent frame for free.


Usage:
    uv run python examples/features/3d/probe_volume.py

Controls:
    Space   - Toggle the volume on/off
    Escape  - Quit

## Source

```{literalinclude} ../../examples/features/3d/probe_volume.py
:language: python
:linenos:
```