I replaced my kitchen "cheapo" fluorescent light last year with a nicer
model that uses F32T8 style bulbs.
After about 4 months, one of the bulbs went bad. These are supposed to
last 5 years. I replaced it. Then the other went bad 3-4 months later.
I went through this a few times.
I tried different bulbs from different brands and stores. No luck. I
thought maybe the ballast went bad so I bought new, good quality, and
replaced that. I did that this past September and now one of the bulbs
is going bad again!
The wiring is fine, all the connections are tight and in correct order.
No signs of burning or charring.
What is going on? How can I fix this? Now I don't even care about the
light...as much as solving my curiosity!!! lol
Seems like you've been through this too many times for it
to be coincidental.
Turn on the lamps for a few hours and then remove the
diffuser to see if there's a build up of heat in the
fitting. It could be warm enough to cause premature
failures without being suffiently hot to show any scorch
or similar marks.
I guess you can check for moisture at the same time
although I wouldn't expect humidity to be a factor.
Remove and reinstall the tube that is showing signs of
failure. Does that help? Perhaps you have some corrosion
or other contaminent building up on the contacts?
Also, is the fitting installed close to a fan, or other
source of vibration? That will certainly shorten the life.
| Malcolm Hoar "The more I practice, the luckier I get". |
Check your manual and check for stickers on your fixture. Often, these
kind of fixtures are very picky on what type of tube they use. Pay
attention to any requirement for a "rapid start" tube, etc. Sometimes
they can be hard to find because they sell out quick.
Other than heat I can't understand what would shorten their life so much. I
have small under the counter fluorescent lamps that only last 6 months or
so. While buying more at HD somebody else was buying the same bulb, I asked
him if he had the same problem. Yep. I replaced two small fixtures under
one cabinet with a longer one (takes a 34" long bulb). On the box GE claims
will last 15,000 hours. Time will tell.
Sounds like defective lamps!
I have just bought ten T8s, mixture of two manuafacturers. No problems
But btw i tried a couple of T8s in an older fixture which uses the
older non-electronic ballast and while they worked the ballast
overheated after a while and became intermittent.
The newer fixtures which use the T8s have electronic ballasts.
I have the same issue with florescent lamps, and in particular with circle
line, and compact fluorescents. The rating on lamp life is based on
continuous burn hours but once you starts turning the fixtures on and off,
it will kill the fluorescents. Remember years ago before the energy crises,
you see floors all lit up 24/7 in high rise buildings - that is for
maintenance so they don't have to change out the lamps as often. My lamps,
like the ones in the hallways and bathrooms where its switched a lot, may
last only six months with a burn life of only 10 or so hours. So at some
point, incandescent lamps will be much more energy efficient than
fluorescents if you take the life-cycle energy cost into account including
the energy to manufacture the lamps.
Actually, lamp manufacturers generally rate fluorescent lamp life
based on three hour starts (3 hours on and 20 minutes off), in
accordance with IES LM-40-1987 testing standards.
Lamp life can be extended by increasing burn cycles but perhaps not as
much as you might expect. For example, a standard GE F32T8 has a
rated life of 20,000 hours based on 3 hours per start and a 24,000
hour life expectancy at 12 hours per start.
A typical CFL would have a rated service life of anywhere from 6,000
to 15,000 hours, based on the aforementioned 3 hour testing cycle. By
comparison, a standard incandescent bulb has a rated life of just
A 100-watt incandescent bulb would consume approximately 100 kWh over
its normal life. At $0.10 per kWh, a consumer would expect to pay
$10.00 in electricity costs to operate this bulb. An equivalent
23-watt CFL would consume 23 kWh over this same timeframe, for a net
savings of $7.70.
A good quality, name brand CFL now costs as little as $2.00 to $3.00
when bought in multi-packs. Given that the cost of energy in the
manufacture and distribution of these bulbs would be a small fraction
of its retail price, even if a CFL were to fail at one-tenth its rated
life (i.e., 1,000 hours versus 10,000 hours), the value of energy it
would have saved would still exceed that of its purchase price.
In any event, I would expect a CFL with a rated life of 10,000 hours
to be capable of withstanding over 3,000 starts (i.e., 3 hours per
start x 3,333 starts = 9,999 hours). If you were to turn this CFL on
and off an average of ten times per day, it should (presumably)
continue to provide service for close to a full year.
If you turn lights on and off more frequently than this, you might
consider a "cold cathode" CFL. These CFLs can be turned on and off as
frequently as you wish, with no material impact on lamp life.
According to my Sylvania catalogue, a standard "general purpose"
60-watt A19 bulb has a rated life of 1,000 hours and its 100-watt A19
counterpart is rated at 750 hours. Sylvania's "double life" bulbs
have a life expectancy of between 1,500 to 3,000 hours depending upon
the wattage. The trade-off in the case of longer life incandescent
bubs is lower light output (fewer lumens per watt).
If you have duty cycles as short as five seconds and you turn your
lights on and off an average of twenty times a day, you should stick
with a halogen or incandescent bulb. Cold cathode CFLs are another
option but as Don points out, these lamps are currently available only
at the lower end of the wattage scale. A 5-watt TCP CC-CFL produces
just 230 lumens or about the same amount of light as a standard
25-watt incandescent. In a six bulb bathroom vanity light that may
not be a problem but for a single socket stairwell fixture it would be
a rather poor choice.
I can see that others have been down this road. I also have a small
"under the counter" light that fails regularly too. The bulbs last for
maybe 6 months at most. They are the T F8 style bulbs. I think they are
9 or 10 inches. I am going to replace the lights completely and go with
what I had before. They may not have been energy savers, but they sure
lasted for years before I had to change them. That alone is going to
save me a lot of money at the rate I am currently spending on bulbs,
Thanks everyone for all the great advice. I appreciate it. Great group!
For what it's worth, I installed six 20-watt T4 fluorescent cabinet
lights about four and a half years ago. The fixture over the kitchen
sink is left on six to eight hours a day, while the others might
average perhaps two or three. So far, I've had to replace just one
tube (the one over the kitchen sink). The lamps have a rated life of
10,000 hours and that seems to be in line with my own experience.
The fixtures are very similar to the ones shown here:
I did remove the plastic sleeve/diffuser so that these fixtures
operate at a lower temperature and I'm hoping this will help extend
the life of both the bulb and ballast (heat being the major killer of
all things electronic).
On 15 Dec 2006 08:25:48 -0800, "Brian"
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