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Repairing and Troubleshooting Fluorescent Fixtures and Tubes

On the home repair scale of 1 to 10 (10 being hardest), repairing a fluorescent fixture is a 3 or 4... fairly simple but some basic electrical skills are necessary, such as being able to identify wires by color, stripping insulation from the ends of cut wires, installing wire nuts and reading instructions.  I added the first and last with tongue in cheek... I know most of you are not color-blind and most of you can read... or you wouldn't be here!

Here are some common fluorescent freak-outs and some suggested solutions!  Note that I will be primarily referring to fixtures using straight fluorescent tubes in this discussion.  Curved tubes work in a similar fashion but have different mounting methods.

I use the term "bulb" and "tube" somewhat haphazardly and inconsistently.  My apologies.  Both are correct, though "tube" is the more correct term and probably a little less confusing.

Fluorescent bulbs designed to replace incandescent bulbs in standard fixtures, such as in recessed lights or table lamps, have all the same features of a fluorescent fixture.  Alas, they cannot be repaired... they must be replaced if they become defective.

Finally, let the buyer beware!!  Parts for some small fluorescent fixtures may cost more than a new fixture!

Troubleshooting dead or flickering fluorescents... could be a bulb, the starter or the ballast!!

A dead fluorescent can be caused by lack of electrical power (tripped breaker or blown fuse), a dead or dying ballast, a dead starter or a dead bulb(s).  Check for power first... then the starter (if applicable) and then the bulbs.  When all else fails, the ballast should be replaced.  Since it is the most expensive item, be sure it really is dead!!  Ahd check the price before you buy... some ballasts are more expensive than new fixtures!!

When flickering is the issue, you still must do the same sort of troubleshooting since all the same problems that can cause a lamp to not work can also cause flickering... defective starters, defective bulbs or a defective ballast.

IMPORTANT:  Flickering fluorescent tubes can cause the ballast to overheat and fail prematurely!  They can even cause a starter to burn out! Don't wait too long to fix the problem or you may end up with a bigger repair!

Testing fluorescent tubes...

First and foremost... look at the bulbs!  If either bulb appears to be very dark near either end the bulb is defective or close to failure.  Note the upper bulb in the left graphic... it is definitely approaching its golden years!  Though this bulb is still producing light its days are numbered.

There is an electrode located inside each end of a fluorescent tube.  Each has two visible pins which fit into the mounting sockets on either end of the fixture.  By testing across these pins you can determine whether or not the electrodes are intact.  Electrically speaking, if there is continuity across the pins, the electrode should be working.  However, even if the electrodes are intact the bulb may not light.  This can occur if some or all of the gas has leaked from the bulb... a condition for which there is no sniff test!  Also, there may be a slight short in the electrodes that gives you a positive reading but the electrode is in fact kablooey!

Thus, the most reliable way to test a fluorescent bulb is to install it into a known working fixture.  If you are troubleshooting a 4-tube fluorescent fixture, this is easy!  Just remove one of the still-working pair of fluorescent tubes and replace it with each of the questionable tubes, one at a time. 99% of the time it will be one of the tubes that is the culprit.

What about pairs of fluorescent tubes?

A flickering fluorescent bulb means that it or one of a dependent pair of bulbs in the fixture has bought the farm. In many fluorescent fixtures, power is sent through a pair of bulbs.  If either bulb is bad, they may both flicker or one may flicker and the other show no life.

My philosophy of sensible repair is to always replace both bulbs.

Fluorescent tubes have such a long life and are so inexpensive (with the exception of some of the "natural light" bulbs) that it makes no sense to skimp.

I acknowledge that replacing all the bulbs is not the most economical's just a practical viewpoint from someone (me) who has been paid to do this type of work for others (you). Fluorescent tubes are an overall economical choice when compared to the alternatives! It just makes more sense to change both tubes at once. To receive a second service call in a month because one of the other bulbs has gone bad is neither desirable from the customer's point of view ($$) or mine (pride in a job done right).

However, if both tubes are functional, the problem is with the ballast or, if applicable, the starter. The starter is replaced first, and if that does not solve the problem, the ballast should be replaced.  Read on...

Does your fixture have a starter?  Maybe... though probably not!

A fluorescent starter is a little gray metallic cylinder that plugs into a socket attached to the fixture's frame.  Its function is to send a delayed shot of high-voltage electricity to the gas within the fluorescent bulb.  The delay allows the gas to become ionized so that it can conduct electricity.  Because this process is not instantaneous, the bulbs will flicker for a few seconds before lighting.  Hence, a defective starter can cause either flickering or total darkness!

Most modern fluorescent fixtures do not use starters, so you might not find one if your fixture is less than 15 to 20 years old.  When determining whether your fixture uses a starter, be sure to look underneath the bulbs... sometimes the bulbs have to be removed first to gain access to the starter.  If you do not see a starter... they are never hidden under any covers or "trap doors"... your fixture is a modern "self-starting" type.

Starters are rated by wattage to the bulbs they will control.  If you have a fixture but have misplaced the starter, write down the wattage of any of the fluorescent tubes and take that information to the hardware store, lest you be scolded by the mean clerk and sent home without supper... or a starter.

Sadly, there is no way for the home handyman to troubleshoot a starter except by replacing it.  Before replacing the existing starter, though, be sure it is securely seated in the base by removing and then reinstalling it.  A starter is installed by pressing it into the socket and then turning clockwise till it locks in place.  To remove a starter, press in and turn counterclockwise... then withdraw the starter.

If you own fluorescent fixtures that use starters, always keep a few handy for troubleshooting purposes!  And don't forget to throw away used ones... most of the time it is impossible to tell the difference between a good and bad starter!

Replacing the ballast (or not) may have unexpected side effects on your wallet!

I'm sure many of you wonder where the name "ballast" came from.  After all, there is the nautical term "ballast" which refers to the contents of tanks on a submarine which control its buoyancy.  Fill the ballast tanks with water and the submarine sinks... with air and it surfaces.

A defective ballast in your fluorescent fixture may make you want to sink it in the nearest pond!  Indeed, the cost of replacing the ballast in a fixture may rival the cost of a new fixture... especially if you want to use a modern electronic ballast that lights the bulbs faster, runs cooler and is virtually hum-free.  (Yes, Virginia, that hum when you flip on the fluorescent lamp is from the ballast, not the bulbs!)

When my customers ask my advice in this matter, I always lean to the aesthetic first.  Do they like the appearance of the fixture?  If not, add one point to the "replace it" side.  Then I confront the ceiling repair issue.  If the new fixture is smaller or has a different "footprint" than the original fixture, the ceiling may need to be repainted to cover the unpainted area under the old fixture.  Sometimes, ceiling texture also has to be touched up after a fixture is taken down!

Smaller fluorescent fixtures, such as those in kitchens to illuminate countertops or built into furniture, follow the same basic criteria.  Since you may have a problem finding an exact replacement fixture (especially if the fixture is very precisely sized), replacing the ballast may be the best choice.

Thus, unless the fixture is absolutely hideous, replacing the ballast is usually the least expensive repair overall when all other factors are considered!

Replacing a ballast... just follow the colors!

To the left is a graphic of a two ballast, four-bulb fluorescent lamp system, with the ballast cover off to expose the wiring.  One look at the spaghetti-like wiring could make anyone lose their appetite!  But get the Rolaids... all is not lost!  Within that snarly mess is order... just follow the colors!

Fortunately, most modern ballasts have a wiring diagram right on the body of the ballast, with the wire colors clearly marked. If not, the diagram will be packed in the box or printed on it.  As if that wasn't enough help, common ballasts often use the same color scheme, making the job about as easy as it can get!

Universal Lighting Technologies has lots of technical info and even a ballast selection tool that is quite thorough.  Visit their site at )

NOTE: Your new ballast may have the same wiring as your old one, but the wiring colors may differ. Be sure to compare them before disconnecting the old ballast.

Choosing the correct ballast...

Needless to say, when you go shopping bring your old ballast with you to assure you get the correct size.  Size is not everything, though.  Since you must purchase a ballast that is wired identically to the existing one, your only choice is the type of ballast, magnetic or electronic.

Magnetic ballasts are the old-time workhorses in the fluorescent world.  They are inexpensive and will give 10 to 20 years of service.  There were some fluorescent fixtures in my father's gas station that were over 40 years old and still working!!

Electronic ballasts are the new guys on the block.  They have some specific advantages over magnetic ballasts.  First, they start more quickly than magnetic ballasts.  Second, they do not hum.  Magnetic ballasts hum right out of the box.  The sound comes from the internal vibrations caused by the magnetic core which supplies power to the bulbs.  As they age, magnetic ballasts tend to get louder and louder... till they finally fail.  Electronic ballasts are silent out of the box and remain so... till death do you part.

Whether the additional cost of an electronic ballast is worth up to double the cost is up to you.  I personally prefer the electronic ballasts because the hum makes me nuts.  It's up to you!

Can you use a dimmer with fluorescent light fixtures?

Yes and no.  Yes, there is a specially-designed dimmer switch that will work with some fluorescent fixtures.  However, this type of dimmer is "ballast-dependent", meaning that each brand of fluorescent dimmer will only work with certain ballasts from certain manufacturers.  In other words, trying to find a dimmer to match your fixture may be a mind-numbing chore.  The ideal situation is to choose the dimmer and the light fixture together to assure compatibility.  Also, these dimmers will not work for incandescent fixtures.  You cannot mix fluorescent fixtures and incandescent fixtures on the same dimmer switch.

The "No" part of this question is that the "conventional" dimmer switches you can purchase at the hardware store are designed for incandescent lighting only, not fluorescent lighting.  If you attempt to use them, the fluorescent fixture may work but only in the full-on position, if at all.

Leaving Fluorescent Lights On... An Energy Saver??

Not necessarily!  As with most things in life, moderation is the key to longevity!  Read our article on the facts and myths around the great fluorescent shutoff!  Click HERE for the full article!

Other resources...

If you want some good technical information of testing ballasts, the most complete source I have found on-line is The Lighting Center, at

If you would like an in depth look at how fluorescent fixtures work, visit "How Stuff Works" for a detailed, high brow explanation, at

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