When fluorescent tubes flicker or go out completely, several different factors can be the culprit. The problem can be because of the electrical power, the ballast, the starter or the tube itself. A dead tube is an easy problem to solve by replacing it with a working bulb. However, you must first determine that the tube is bad. To do this, you need to test the fluorescent tube.
Turn the light switch off, and carefully remove the fluorescent tube from the light fixture. A fluorescent tube is held in place by the metal electrodes on the ends. Twist the bulb, and then slide the electrodes up through the holder to remove it.
Examine both ends of the tube. Check for darkened or blackened areas. If these are visible, the bulb is no longer good or is going bad. In this case, you know the bulb needs replacing. If the ends look normal, carry out further testing.
Place a continuity meter on each set of metal electrodes of the bulb and check the meter reading. The reading needs to be 0 ohms to indicate continuity. If the reading is not 0, the bulb is bad and needs replacing.
Remove a bulb from a working fluorescent fixture, and replace it with the one you are testing. Test each tube in a pair one at a time. If the tubes work, you know they are good and the fixture is the problem.
Before replacing both bulbs in a fixture, test the bulbs separately. Fluorescent bulbs can work in twos if wired together as a pair in the fixture. One bad bulb can cause the other bulb to flicker or not work.
Gas leakage and shortages can cause a meter to give a false positive reading on a fluorescent bulb. Therefore if you feel that the reading might not be accurate, check the bulb using a different method, such as placing it in a working fixture.