Best way to make blinking light

Im pretty sure a plain boolean would do a rescource-friendly job but it might not look as good as a intensity-changer.

If you want to change the intensity smoothly try something like this:

 using UnityEngine;
 using System.Collections;
 
 public class Flash : MonoBehaviour
 {
 
     public float totalSeconds;     // The total of seconds the flash wil last
     public float maxIntensity;     // The maximum intensity the flash will reach
     public Light myLight;        // Your light
 
     public IEnumerator flashNow ()
     {
         float waitTime = totalSeconds / 2;                        
         // Get half of the seconds (One half to get brighter and one to get darker)
         while (myLight.intensity < maxIntensity) {
             myLight.intensity += Time.deltaTime / waitTime;        // Increase intensity
             yield return null;
         }
         while (myLight.intensity > 0) {
             myLight.intensity -= Time.deltaTime / waitTime;        //Decrease intensity
             yield return null;
         }
         yield return null;
     }
 }
 

As you can see this method is a CoRoutine. If you are not familiar with them check this link: http://docs.unity3d.com/ScriptReference/MonoBehaviour.StartCoroutine.html

Good luck! :)