You can troubleshoot and repair flickering fluorescent bulbs, but be aware that sometimes it costs more to repair a bulb or fixture than it does to replace it. If you have a flickering fluorescent bulb, address the problem right away because flickering can cause the ballast to overheat or fail.
If a fluorescent bulb is flickering, there is likely a problem with the bulb itself. If the bulb is very dark on either end, it may be defective and burnt out, even though it is new. If you can't see a problem with the bulb, test it. The best way to test a bulb is to put it into a fixture you know works. If the bulb doesn't work or flickers in a working fixture, you know the problem is with the bulb and not the fixture.
The problem could be with a starter in the bulb, but most bulbs made within the past 15 to 20 years do not have starters. If your bulb does have a starter, you will be able to see it at the bottom of the bulb. Fluorescent starters look like grey metallic cylinders. If the problem is with the starter, the only thing to do is to replace either the starter or the entire bulb.
If the air around the bulb is very cold and is circulating, the bulb won't be able to generate enough heat to work properly, which may lead to flickering. The internal temperature of a fluorescent bulb must be about 10 degrees C in most cases, and if it does not reach this, it may flicker, dim or not work at all. If the air around the bulb is too cold, you can use an enclosed light fixture to help insulate the bulb.
You should also be aware that nearly all fluorescent bulbs require a warm up time. Although newer bulbs need less time to warm up than older bulbs, they require a second or two. The bulb may flicker during this short warm up.
Depending on your ballast, you may be using the wrong kind of fluorescent bulb. If you can't find any other problems with the bulb, check with the ballast's manufacturer to see if there are particular kinds of fluorescent bulbs the ballast must work with.
If the problem isn't with the bulb, it is probably with the fixture. Make sure you do not connect a fluorescent bulb to a dimmer switch. Most fluorescent lights cannot be used with dimmers, so if they work at all, they will probably flicker.
The Natural Handyman notes that while it is rare for a ballast to fail completely, it does happen. So, if you test the bulb in a known working fixture and the bulb does work properly, it may be time to replace the ballast.