How to Replace a Fluorescent Lightbulb. Changing a burned-out fluorescent lightbulb is only a bit harder than replacing a conventional one. Here we'll walk you through it and help troubleshoot a couple of possible problems.
Replace the Bulb
Make sure the light switch is turned off.
Remove the lens or diffuser to access the bulb. On most fluorescent lights, the lens or diffuser is a plastic panel below the bulb. Push the panel up and tilt to remove.
Check to make sure that the problem isn't something so simple as a poor contact. This can usually be corrected by giving the bulb a gentle turn a few degrees and then back to the lock position.
Hold the old bulb firmly at one end, and rotate it one quarter-turn clockwise. This should put the end prongs in line with the loading slot.
Slide the bulb free.
Lower the end of the bulb carefully out of the socket. When one end is free, pull slightly and the other end should come out also.
Set the old bulb aside and lift a new bulb into the fixture.
Hold the bulb horizontally, and rotate the new bulb until the prongs on each end are lined up with the grooves in the socket.
Insert the prongs in the socket and rotate the bulb a quarter-turn in a counterclockwise direction. The bulb should click into place on each end.
Test the light at the switch. If the light still doesn't come on you may need to replace the ballast.
Replace the Ballast
Find the ballast, usually seated near one end of the bulb. It is a silver, cylinder-shaped item with a diameter similar to that of a quarter. The ballast provides the starting voltage and then stabilizes the current for the fluorescent bulb.
Loosen the ballast by turning it 1/4- to 1/2-turn counterclockwise.
Pull the ballast out of fixture and take to hardware store to match with a new one.
Insert a new ballast into the light fixture; twist clockwise to lock into position.
Replace the lens cover.