Sounds pretty straightforward. If changing the bulb don't fix it,
the root cause is likely not the bulb. If you have two choices and it
ain't one, it's likely the other...assuming there's only two choices...
If it is not the bulbs, it could be the ballast, however the lamp
holders themselves could also be to blame, or a connection
that has become loose or corroded...
It is fairly easy to figure out:
Inspect the lamp holders, if they look damaged or melted
then replace them... If they don't appear damaged then
examine all the connections one wire nut at a time --
if none of them are loose or show signs of arcing, then
remove the ballast and take it to the electrical supply
house and obtain an identical replacement...
Odds are however that your problem is with the ballast,
but it is always good to check everything else also
because it only takes one break in the circuit inside
the light somewhere for the lamp(s) to not light...
That has not been the case on any of the 4' or 8' light fixtures
that I have worked on in the past and some of them had up to 4
lamps being powered by the same ballast...
Sometimes there are connections within the light from the
ballast that if they loosened would open the circuit to 2
lamps at the same time... But they aren't like the old
fashioned Christmas lights where if one lamp goes out
all of them go out... Multiple lamps fed off the same
circuit on the ballast are wired in parallel so each would
remain lit independent of the other, they would have to
be wired in series for one lamp to kill a circuit...
Be sure the bulbs are touching all the contacts in the sockets. Those
sockets do break. If that's ok, then is there a starter? In old
fixtures there were these small starters that look like 3/4 inch round
by 1.5 inch tall (roughly). Those go bad. If it's a newer fixture,
you only have one choice left, the ballast. Of course a new bulb
could be bad too..... Get a 3rd bulb and replace one at a time before
buying a ballast or new fixture. If you replace the ballast, get an
electronic one. They are better than the old transformer type.
When I was in the Coast Guard we used to hold fluorescent tubes next
to our 100KW Loran-C tower and light them up. Obviously we were *much*
farther away than an inch or so!
The cool part was when you held the end of the tube in one hand and
slid your other hand up the tube. The tube would only light above your
hand so you could "silde" the light up and down the tube.
If changing bulbs does not help, then the problem is probably either
in the ballast or with wiring - such as a broken or corroded connection.
When a fluorescent bulb burns out, there is usually a characteristic
blackening of 2-3 inches (or so) of one end, occaisionally both ends.
If the problem is a failed ballast, I would suggest replacing the entire
fixture with two 4-foot fixtures. Preferably, one using 1-inch-diameter
(T8) 32-watt 4-footers, and having a modern electronic ballast. The
economics get better, the bulbs are easier to replace, and a better choice
of colors and color rendering properties is available with 4-foot bulbs
than with 8-footers.
More fluorescent bulbs are manufactured in 4-foot length than in all
other lengths combined. 4-footers usually cost less than all other sizes
of fluorescent bulbs. Most of the lumens of light produced by
fluorescents worldwide are produced by 4-footers.
If you have a problem with the ballast or the fixture, then I think
it's a good idea to "go with the flow" and change to 4-foot.
- Don Klipstein ( firstname.lastname@example.org)
Four foot tubes are also a lot easier to dispose of. Around these parts,
fluorescent tubes are considered to be hazardous waste, but any tube up to
four foot long can be disposed of free at several participating merchants
(the local ACE hardware being one of them).
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