Although there may be a couple of reasons why a tubular fluorescent light bulb is flickering or not working at all, the easiest way to tell if it needs changing is to look at the ends of the tube. A dark gray- or black-colored end(s) on the tube will be a clear indication that the tube needs to be replaced.
Unplug the fluorescent light unit from the electrical socket.2
Hold the fluorescent tube near its center with both hands, and twist the bulb in the fixture 45 degrees.3
Look into one of the terminal ends to align the two-pronged element of the tube to the end of the fluorescent light fixture. Aligning the prongs vertically to the fixture will allow you to extract the bulb straight down. Remove the bulb and place it carefully out of the way where it will not tip over or roll off a countertop and shatter.4
Align the two-pronged element of the new bulb vertically to the light fixture and push upward until it has reached the top of the fixture.5
Twist the bulb 90 degrees, making sure both dual-pronged elements are correctly inserted into the fixture.6
Plug the light back into the electrical outlet and turn the light back on.7
Dispose of the spent fluorescent light bulb tube in accordance with your city's hazardous waste material regulations.