When a lamp is at the end of its life cycle, the filament inside the lamp becomes thinner and thinner and eventually a small gap or notch will form. This notch creates a “short” within the lamp and keeps it from coming on. Sometimes the notch is very small and when the fixture is gently “tapped” the filament fuses back together and the fixture will operate!

Once the system is turned off, the filament cools and separates again. The following evening, the lamp does not respond, until gently tapped. When this occurs, the lamp has virtually reached the end of its life cycle and requires replacement.