Have you ever had a light fixture flicker on and off? There are many things that can cause this problem. It could be in the light switch. When you turn the light on place your ear near the light switch, can you hear a sizzling sound when the light is flickering. If so you need to replace the switch. You can also do this at the fixture. Of course use common sense and don't get burned by the bulb, these things can get very hot! It might not seem obvious at first but look at picture 1 (click on the picture to get a larger view). This is a standard porcelain light bulb socket. This is the view you have once the bulb is removed. Look at the small brass circle near the top of the socket. See the black residue around it? The black area is where this socket has been arcing. The neutral or white wire is connected to this terminal. This fixture would work fine for a while the cut on/off randomly. There is no "fix" for this problem except to replace the socket.

The second picture is the top of the socket. Here you can see how the wires are riveted to the porcelain housing. This type of electrical fault is a major contributor to house fires. This connection, if not repaired, will continue to get worse and will eventually build up heat and possibly catch the fixture on fire.

The newly developed Arc Fault Circuit Breakers constantly monitor the electrical circuit looking for arcing characteristics. When this type of breaker detects arcing it trips. Breakers no longer trip from a short circuit which typically sends current directly to a grounded source or from overload which means the circuit is pulling more power than it was designed for, they will detect arcing before a major problem arises.