Bob Miller wrote:
On Wed, 6 Aug 2008 22:38:20 -0400, "Hal Rosser"
wrote:

Interesting, but from past experience, the results may be just the opposite
a few months later because the source of the components may change over
time.
The components of fluorescent fixtures consists of
The ballast - which is usually outsourced by the fixture manufacturer.
Ballast types vary - GE, Universal, Advance, and several other Ballast
makers sell to fixture manufacturers.
The sockets - usually made by Leviton or Eagle or Rodale - but there are
others.
The lamp (the fluorescent lamp). Usually are not provided by the fixture
manufacturer. Made by Phillips, GE, Sylvania, etc.
Some even have a 'starter'.
--I expect the ballast is the critical component - some are magnetic, some
are electronic - its probably the culprit

I'm curious, what does the ballast do? I see it referred to on light
fixtures I've installed, but I've never quite figured out what it is.




All these bulb work by passing current through an ionized gas. The
forward voltage drop across the tube goes down as current goes up ( a
so-called negative resistance characteristic). If there weren't
something to limit the current, it would rise to the point of
destruction. You could use a resistor, but it's lossy. All you need is
some impedance, so an (almost lossless) inductor works fine. That is,
hook up an inductor with a reactance of 100 ohms to a 100Vac source, and
you'll get a current of 1 Amp, but no power is consumed because the
current is out of phase with the voltage.

You could also use a constant current regulator to do the same thing.
If the regulator is a variable duty cycle switcher, then the loss can be
quite low. That's what's in the electronic ballast... essentially a
constant current source.

In practice, there's some more aspects to getting a fluorescent lamp
started.. you have to ionize the gas inside, which you can do either
with a filament (gets things rolling, and once current is flowing, the
current in the gas keeps it ionized) or with a high voltage pulse (like
a flash tube).. (this is the difference between the "thermal starter"
where you see the tube glow reddish at the ends at the beginning, and
the "rapid start" types)

(This is also why fluorescent lamps are dimmer/harder to start in cold
temperatures..)



Where the term "ballast" came from, I don't know.