Arduino LDR Sensor to Play Audio Clip At A Certain Level

I am trying to get information from a simple LDR light sensitive Resistor to trigger an audio clip in Unity 3D. I can get the clip to play but it overlaps and repeats the audio. What I want it to do is activate an audio clip from a random array of audio clips. How can I do this? This is the code I have.

 using UnityEngine;
 using System.Collections;
 using System.IO.Ports;
 using System.Threading;
 
 public class Sending : MonoBehaviour {
 
     //Random Clips
     public AudioClip[] voices;
     public GameObject worldLight;
     public static Sending sending;
 
     //public static SerialPort sp = new SerialPort("COM4", 9600, Parity.None, 8, StopBits.One);
     public static SerialPort sp = new SerialPort("/dev/cu.wchusbserial1420", 115200);
 
     public string message2;
 
 
 
     void Awake () {
         if (sending == null) {
             DontDestroyOnLoad (gameObject);
             sending = this;
         } else if (sending != this) {
             Destroy (gameObject);
         }
         
     }
 
 
     float timePassed = 0.0f;
     // Use this for initialization
     void Start () {
         OpenConnection();
     }
     
     // Update is called once per frame
     void Update () {
         //timePassed+=Time.deltaTime;
         //if(timePassed>=0.2f){
 
             //print("BytesToRead" +sp.BytesToRead);
             message2 = sp.ReadLine();
             print(message2);
         //    timePassed = 0.0f;
         //}
 
         if (message2!="") {
             print("called");
             lightMeUp(message2);
         }
     }
 
     public void OpenConnection() 
     {
        if (sp != null) 
        {
          if (sp.IsOpen) 
          {
           sp.Close();
           print("Closing port, because it was already open!");
          }
          else 
          {
           sp.Open();  // opens the connection
           sp.ReadTimeout = 16;  // sets the timeout value before reporting error
           print("Port Opened!");
         //        message = "Port Opened!";
          }
        }
        else 
        {
          if (sp.IsOpen)
          {
           print("Port is already open");
          }
          else 
          {
           print("Port == null");
          }
        }
     }
 
     void OnApplicationQuit() 
     {
        sp.Close();
     }
 
     public static void sendYellow(){
         sp.Write("y");
     }
 
     public static void sendGreen(){
         sp.Write("g");
         //sp.Write("\n");
     }
     
 
     public static void sendRed(){
         sp.Write("r");
     }
 
 
     public static void sendBlue(){
         sp.Write("b");
     }
 
     public static void sendBlue2(){
         sp.Write("1");
     }
 
     public static void sendPulse1(){
         sp.Write("p");
     }
 
     public static void sendPulse2(){
         sp.Write("q");
     }
 
     void lightMeUp(string message){
         print (message);
         float fl = float.Parse (message) / 100.0f;
         fl = 1.0f - fl;
 
 
             //Do Something
             GetComponent<AudioSource> ().PlayOneShot (voices [Random.Range (0, voices.Length)]);
 
     }
 
 }