Understanding Probe Volumes

A Probe Volume is a group of Light Probes that Unity places automatically based on the geometry density in your Scene, to create baked indirect lighting. You can use Probe Volumes instead of manually placing and configuring Light Probes.

Advantages and limitations

Feature Light Probe Groups Probe Volumes
Selection of surrounding probes Per GameObject Per pixel
Optimize memory use with streaming No Yes
Place probes automatically No Yes
Blend between different bakes No Yes
Place probes manually Yes No

Probe Volumes have the following advantages:

  • Unity samples surrounding probes per-pixel rather than per GameObject. This sampling approach results in better lighting consistency, and fewer seams between adjacent GameObjects.
  • If you use volumetric fog, the per-pixel probe selection provides more accurate lighting for the variations in a fog mass.
  • You can adjust Light Probe layouts across a scene, for example using a denser set of Light Probes in an interior area with more detailed lighting or geometry. Refer to Configure the size and density of Probe Volumes for more information.
  • Probe Volumes work well if you work with multiple scenes. Refer to Baking Sets for more information.
  • Because Probe Volumes can cover a whole scene, screen space effects can fall back to Light Probes to get lighting data from GameObjects that are off-screen or occluded. Refer to Screen Space Global Illumination for more information.
  • Unity can use the data in Probe Volumes to adjust lighting from Reflection Probes so it more closely matches the local environment, which reduces the number of Reflection Probes you need. Refer to Frame Settings properties.
  • Probe Volumes include streaming functionality to support large open worlds.


The car model is made up of separate GameObjects. The left scene uses Light Probe Groups, which use per-object lighting, so each part of the car samples a single blended probe value. The right scene uses Probe Volumes, which use per-pixel lighting, so each part of the car samples its nearest probes. This image uses the ArchVizPRO Photostudio HDRP asset from the Unity Asset Store.


In the left scene, Reflection Probe Normalization is disabled. In the right scene, Reflection Probe Normalization is enabled, and there's less specular light leaking on the kitchen cabinet. This image uses the ArchVizPRO Interior Vol.5 HDRP asset from the Unity Asset Store.

Probe Volumes have the following limitations:

  • You can't adjust the locations of Light Probes inside a Probe Volume. You can use settings and overrides to try to fix visible artifacts, but it might not be possible to make sure Light Probes follow walls or are at the exact boundary between different lighting areas. Refer to Fix issues with Probe Volumes for more information.
  • You can't convert Light Probe Groups into a Probe Volume.

How Probe Volumes work

HDRP automatically fills a Probe Volume with a 3D structure of 'bricks'. Each brick contains 64 Light Probes, arranged in a 4 × 4 × 4 grid.

HDRP uses bricks with different sizes to match the amount of geometry in different areas of your scene. For example, in areas with more geometry, HDRP uses small bricks with a short distance between Light Probes. The Light Probes capture lighting at a higher resolution, so lighting is more accurate.

The default Light Probe spacing is 1, 3, 9, or 27 m.


In this screenshot from the Rendering Debugger, the small purple bricks contain Light Probes spaced 1 meter apart, to capture data from high-geometry areas. The large blue bricks contain Light Probes spaced 3 meters apart, to capture data from areas with less geometry.

Each pixel of a GameObject samples lighting data from the eight closest Light Probes around it.

You can do the following:

Baking Sets

To store lighting from a scene in a Probe Volume, the scene must be part of a Baking Set.

A Baking Set contains the following:

  • One or more scenes, which optionally include Probe Volumes.
  • A single collection of settings.

By default, HDRP uses Single Scene mode, and places each scene in its own Baking Set automatically. However, only one Baking Set can be active at any time, so if you work with multiple scenes, you must add these scenes to a single Baking Set if you want to bake them together. Refer to Bake multiple scenes together with Baking Sets for more information.

Lighting Scenarios

A Lighting Scenario asset contains the baked lighting data for a scene or Baking Set. You can bake different lighting setups into different Lighting Scenario assets, and change which one HDRP uses at runtime, or blend between them.

Refer to Bake different lighting setups with Lighting Scenarios for more information.

How Lighting Scenarios store data

Probe Volumes splits Lighting Scenario data into two parts, to avoid duplicating data:

  • The shared data, which contains mainly the scene subdivision information and probe placement.
  • The per scenario data, which contains the probe lighting information.

HDRP can't share the data or blend between Lighting Scenarios if you move geometry between bakes, because the Light Probe positions might change. Refer to Keep Light Probes the same in different Lighting Scenarios for more information.

Additional resources