Mesh.normals  

// Rotate the normals by speed every frame

var speed = 100.0;

function Update () {
    var mesh : Mesh = GetComponent(MeshFilter).mesh;
    var normals : Vector3[] = mesh.normals;

    var rotation : Quaternion = Quaternion.AngleAxis(Time.deltaTime * speed, Vector3.up);
    for (var i = 0; i < normals.Length; i++)
        normals[i] = rotation * normals[i];

    mesh.normals = normals;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public float speed = 100.0F;
    void Update() {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Vector3[] normals = mesh.normals;
        Quaternion rotation = Quaternion.AngleAxis(Time.deltaTime * speed, Vector3.up);
        int i = 0;
        while (i < normals.Length) {
            normals[i] = rotation * normals[i];
            i++;
        }
        mesh.normals = normals;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public speed as single = 100.0F

    def Update():
        mesh as Mesh = GetComponent[of MeshFilter]().mesh
        normals as (Vector3) = mesh.normals
        rotation as Quaternion = Quaternion.AngleAxis((Time.deltaTime * speed), Vector3.up)
        i as int = 0
        while i < normals.Length:
            normals[i] = (rotation * normals[i])
            i++
        mesh.normals = normals