# sphericalHarmonicsCoefficients Data containing spherical harmonics coefficients that describe the light’s intensity in all directions. ``` var sphericalHarmonicsCoefficients: Data? { get } ``` ## 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:)`](/documentation/ModelIO/MDLPhotometricLight/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`](/documentation/ModelIO/MDLPhotometricLight/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.) ```swift func numberOfCoefficients(at level: Int) -> Int { return (level + 1) * (level + 1) } func offsetForLevel(_ level: Int) -> Int { return numberOfCoefficients(at: level - 1) - 1 } guard let coeffs = light.sphericalHarmonicsCoefficients else { fatalError("light does not have spherical harmonics") } let totalCount = numberOfCoefficients(at: light.sphericalHarmonicsLevel) let offset = offsetForLevel(2) // level 2 has three sets of coefficients, at indexes 3...5 let index = 1 // get the second of 3 coefficients on level 2 (zero-based index) coeffs.withUnsafeBytes { (bytes: UnsafePointer) -> () in let red = bytes[offset + index] let green = bytes[totalCount + offset + index] let blue = bytes[totalCount * 2 + offset + index] } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)