Is There a Fault in a Fiber?

This is a visible fiber, visible light source, visual. So it's used for locating faults and fiber by shooting what, like a visible light. As you plug that into the one end of the fiber and then you hold it up and you can see the light come out the other end. It's no different than using like a toner on a, on an electrical cable. You put something that's generating noise on one side or an electrical signal on one side and you can pick it up on the other.