---
title: sphericalHarmonicsCoefficients
framework: modelio
role: symbol
role_heading: Instance Property
path: modelio/mdlphotometriclight/sphericalharmonicscoefficients
---

# sphericalHarmonicsCoefficients

Data containing spherical harmonics coefficients that describe the light’s intensity in all directions.

## Declaration

```swift
var sphericalHarmonicsCoefficients: Data? { get }
```

## Discussion

Discussion Spherical harmonic coefficients describe the distribution of light around a light source with less high-frequency detail than a cube map texture, but they can be used more efficiently in real-time rendering. Use the generateSphericalHarmonics(fromLight:) method to create spherical harmonics data based on the light’s photometry data. The data is an array of 32-bit floating-point values, containing three noninterleaved data sets corresponding to the red, green, and blue sets of coefficients. The array’s length is determined by the sphericalHarmonicsLevel property: At level 0, the array has 1 coefficient (3 values). At level 1, the array has 4 coefficients (3 sets of 4 values, 12 values total). At level 2, the array has 9 coefficients (3 sets of 9 values, 27 values total). At level 3, the array has 16 coefficients (3 sets of 16 values, 48 values total). Spherical harmonics levels beyond 3 are not supported. For example, the code below shows how to access the second coefficient at level 2. (Note, however, that typically a renderer passes the entire data buffer to a GPU-based shader and uses equivalent shader code to extract individual coefficients.)

## See Also

### Interpreting the Light Web as Spherical Harmonics

- [generateSphericalHarmonics(fromLight:)](modelio/mdlphotometriclight/generatesphericalharmonics(fromlight:).md)
- [sphericalHarmonicsLevel](modelio/mdlphotometriclight/sphericalharmonicslevel.md)