If you have a florescent light in your home that likes to act up sometimes there may be a quick fix or the bulbs might just be cold but sometimes the ballast can go bad and require replacement.
How do you figure out if it is something small or a new part is required?
The first thing you want to do is turn the fixture on and let it run for about a minute. If it is cold in the room or if the ceiling is the other side of an unheated attic the bulb and fixture can get cold enough that the gasses in the bulb need time to warm up. This is a normal condition and it is one drawback of florescent lighting. This often happens in unheated garages where people install drop lights but it may happen anywhere including a cold basement.
If the bulb warms up and works correctly within a minute or two then there really nothing that you can do to cure this problem other than checking if insulation has moved above the bulb in an attic or checking for air leaks around the fixture that are letting in cold air.
You can also opt to replace the bulbs with LED light bulbs but these bulbs often have slightly less light output. If you do use LED they will work without flickering in very cold conditions.
If the light continues to flicker after a minute or two of heating up the problem could be the bulb. If you have a replacement you can try replacing it but you can also just check if the bulb is loose in its socket. Both of these things are possibilities. If you have a dual fixture or a replacement bulb where you can swap bulbs and the new or working bulbs do not cure the problem then you probably need to replace the ballast in the light fixture.
The Ballast in a Florescent bulb controls the electricity for the bulb and they can go bad. Often when a ballast goes bad the light will not turn on at all however flickering could also be a problem if you have already gone through the previous steps of allowing the light to run until it warms up and replacing the bulb with a known good one.
Replacing a ballast is not the most difficult thing to do but you will be working on a fixture that could be hardwired to your home’s wiring. If the fixture is a plugin model used in a garage you can unplug it from the outlet and be safe. If it is hardwired you will need to turn off the circuit breaker to the fixture and not rely on just turning off the wall switch. Very often electricians make mistakes and switch the wrong part of a circuit and this can result in a hot wire in the electrical box even if the wall switch is off.
To protect yourself you should always use a non-contact voltage tester that will sound an alarm and blink if you get the tip near a hot / energized wire. They only cost about $15 and are an important tool in everyone’s tool box.
Follow the instructions on ballast selection or remove the one you have and bring it to the home store for matching. You might even need to go to a specialized electrical supply house if the fixture is old. Also if you are considering upgrading to LED bulbs then you should ask about a compatible ballast or some LED bulbs actually require you to remove the ballast so if your ballast is bad upgrading to LED might really be worth it at this time.
Final Note
It is important to work safe when working on your lighting fixtures.
Always turn your fixtures off before you change bulbs and never work on wiring unless the fixture is unplugged or the circuit breaker is turned off. Never rely on wall switches and use a voltage tester.
If your fixture is in cold conditions there is not much you can do but let it flicker until it warms up. For this reason upgrading to LED bulbs can be worth the cost.