How to make flashing/blinking/flickering lights?

I would probably use Random.Range to generate a random number each frame and then animate the light based on that.

Something like this (probably after some major tweaking):

 randNmbr = Random.Range(-1.0, 1.0);
 
 light.intensity += randNmbr;
 
 if(light.intensity > 1.0)
     light.intensity = 1.0;
 
 if(light.intensity < 0.0)
     light.intensity = 0.0;