Mesh.normals

Description

The normals of the Mesh.

If the Mesh contains no normals, an empty array is returned.

// Rotate the normals by speed every frame

using UnityEngine;

public class ExampleClass : MonoBehaviour
{
    float speed = 100.0f;

    // Update is called once per frame
    void Update()
    {
        // obtain the normals from the Mesh
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Vector3[] normals = mesh.normals;

        // edit the normals in an external array
        Quaternion rotation = Quaternion.AngleAxis(Time.deltaTime * speed, Vector3.up);
        for (int i = 0; i < normals.Length; i++)
            normals[i] = rotation * normals[i];

        // assign the array of normals to the mesh
        mesh.normals = normals;
    }
}

Note: To make changes to the normals it is important to copy the normals from the Mesh. Once the normals have been copied and changed the normals can be reassigned back to the Mesh.