Why does Unity tetrahedralization fail with my probe placement?

Tetrahedralization needs probes spread in 3D, not all on the same plane. A flat ring of probes around a room produces a degenerate triangulation. Add probes at varied heights, especially near the ceiling and floor, so the probe volume forms tetrahedra.

Why do dynamic objects look unlit between rooms?

There is a hole in the probe volume. Place at least one probe in each enclosed space, and ensure probes connect across doorways. Visualize via Lighting > Light Probe Visualization to see gaps.

How do I add a probe at the sky for outdoor scenes?

Place a probe at high altitude above your playable space. The bake captures sky lighting; dynamic objects above the ground volume sample correctly. Without it, jumping characters can suddenly go dark when leaving the probe convex hull.

Fix: Unity Light Probe Tetrahedralization Fails

Quick answer: Tetrahedralization needs probes distributed in 3D. All-coplanar probe placements produce degenerate triangulation. Add probes at multiple heights (floor, head, ceiling) and at least one near the sky for outdoor scenes.

Here is how to fix Unity Light Probe systems that warn about tetrahedralization failure, leave dynamic objects unlit in some areas, or produce sudden dark patches when characters move between rooms. Light probes need 3D distribution; flat rings of probes form degenerate volumes that the engine cannot interpolate over.

The Symptom

Console warning: Light probe placement is degenerate; tetrahedralization may fail. Dynamic objects (NPCs, player) appear flat-lit or unlit in certain areas. Crossing certain spots produces sudden lighting changes.

What Causes This

Coplanar probes. Light Probe Group with all probes at Y=0 produces a flat plane; the engine cannot tetrahedralize a flat point set.

Holes in coverage. Probes around a doorway but none inside the next room leaves a gap; objects in the gap fall outside the probe convex hull.

No sky probe. Outdoor objects above ground level fall outside the volume; sample wrong.

Probe Group inactive. An inactive probe group’s probes do not contribute. Verify groups are enabled.

The Fix

Step 1: Add probes at multiple heights. For each room, place probes at:

Floor level (~0.1 m)
Waist level (~1 m)
Head level (~1.7 m)
Ceiling (~2.5 m)

This forms tetrahedra throughout the volume.

Step 2: Cover doorways with probes. Place probes at the threshold of each room transition, both inside and outside, so the volume connects continuously.

Step 3: Add a high sky probe for outdoor scenes. Place at least one probe well above the playable area (e.g., 50 m up). Captures sky color; dynamic objects above ground sample it.

Step 4: Use multiple Light Probe Groups for clarity. Per-room groups make placement maintainable. Unity merges them into a single tetrahedralization.

Step 5: Visualize and verify. Open Window → Rendering → Lighting. Enable Light Probe Visualization. Walk dynamic objects through your scene; the probe blend cells should color them correctly without abrupt changes.

Use Adaptive Probe Volumes For Easier Setup

Unity 2022+ added Adaptive Probe Volumes (APV) which auto-place probes based on geometry. Switch from Light Probe Groups to APV for a far smoother experience — no manual probe placement needed.

“Probes need 3D distribution. Multi-level placement avoids tetrahedralization failure. Sky probe for outdoors. APV for the easy life.”

Related Issues

For lightmap leaks, see Baked Light Leaks. For bake stalls, see Lightmap Bake Stuck.

Floor, head, ceiling. Cover doorways. Sky probe. The dynamic objects light correctly.