Version: 2021.1
Light Probes
Light Probe Groups

Light Probes: Technical information

The lighting information in the light probesLight probes store information about how light passes through space in your scene. A collection of light probes arranged within a given space can improve lighting on moving objects and static LOD scenery within that space. More info
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are encoded as Spherical Harmonics basis functions. We use third order polynomials, also known as L2 Spherical Harmonics. These are stored using 27 floating point values, 9 for each color channel. Even though Unity is using Geomerics’ Enlighten, we use a different SH basis than what you find on their blog (y and z axes are swapped). Unity is using the notation and reconstruction method from Peter-Pike Sloan’s paper, Stupid Spherical Harmonics (SH) Tricks, and Geomerics are using the notation and reconstruction method from Ramamoorthi/Hanrahan’s paper, An Efficient Representation for Irradiance Environment Maps.

The Unity shaderA program that runs on the GPU. More info
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code for reconstruction is found in UnityCG.cginc and is using the method from Appendix A10 Shader/CPU code for Irradiance Environment Maps from Peter-Pikes paper.

The data is internally ordered like this:

                        [L00:  DC]

            [L1-1:  y] [L10:   z] [L11:   x]

  [L2-2: xy] [L2-1: yz] [L20:  zz] [L21:  xz]  [L22:  xx - yy]

The 9 coefficients for R, G and B are ordered like this:

L00, L1-1,  L10,  L11, L2-2, L2-1,  L20,  L21,  L22, // red channel

L00, L1-1,  L10,  L11, L2-2, L2-1,  L20,  L21,  L22, // blue channel

L00, L1-1,  L10,  L11, L2-2, L2-1,  L20,  L21,  L22  // green channel

For more “under-the-hood” information about Unity’s light probe system, you can read Robert Cupisz’s talk from GDC 2012, Light Probe Interpolation Using Tetrahedral Tessellations”, GDC 2012


  • 2017–06–08 Page published

  • Light Probes updated in 5.6

Light Probes
Light Probe Groups