Mini Electric Fence Light Bulb flashes with every pulse of the fence, Predator Light Emits A "Knocking" Sound When Fence Charger is Working Properly Can be seen up to 1 mile or more away, 360 degrees and from the air Recommended for fence chargers 3 Joule and Higher for optimal brightness See YouTube Video: https://youtu.be/Rzl1k4CEMOY