How to determine angle degrees distance of one object from another?

I am pretty sure that directly behind you would be 180 degrees.

You want to use Vector3.Angle . It takes in a from Vector3 and a to Vector3 and returns the angle between the two. If I understand you correctly, you'll have your head angle which is, at the start, this flashing light reference point. If you're staring at that, it's effectively your Camera's transform.forward. This is your from. Your to is your target's position - the camera's transform.position.

So if this script were to be attached to your camera it would look like this:

 using UnityEngine;
 using System.Collections;
 
 public class AngleTest : MonoBehaviour {
 
     public Transform targetTransform;
 
     // Update is called once per frame
     void Update ()
     {
         if (targetTransform != null)
         {
             float angleToTarget = Vector3.Angle(transform.forward, targetTransform.position - transform.position);
             Debug.Log("Angle to target is: " + angleToTarget);
         }
     }
 }