In article , Jeff Wisnia wrote:
Blue wrote:
I investigated the missing ground theory in howthings work" and was
fascinated by what it said. Seems that the flourescent metal box should be
grounded to give reliable ionization of the tubes. that's a new one on me
and still puzzles me. E.g., I have a two tube flourescent fixture in my
garage with a two prong plug feeding it with no problem.

snipped

Grounding of the metal "reflector" above the bulbs is not always
essential, but can be helpful if the ballast (or maybe the bulbs) are a
little wimpy. The symptoms of an ungrounded fixture can be bulbs glowing
just at their ends, but not "firing up" all along their length.

TRUE!

If the bulbs glow throughout their length, grounding is not the problem.

When grounding is the problem, the ill effects of lack of grounding may
be intermittent, and may vary with temperature and/or humidity.

The grounding works by providing an electrode to create an electrostatic
field extending away from the electrodes at the ends of the bulbs.
That field helps get the ionization of the gas (mercury vapor)inside the
tube extend the full length of the bulb.

Close enough and I would award a cigar!

The way I see it, grounding makes unionized gas in most of the length of
the bulb more alike in potential, and that increases the voltage gradient
(electric field) in the gas approaching the electrode at either end of the
bulb - which is where ionization of the gas normally starts. Once
ionization happens where it can be initiated, then the boundary between
ionized gas and unionized gas is where the voltage gradient is high -
resulting in ionization there, and thus the boundary between ionized and
unionized gas propagates (usually in quite a small fraction of a second if
at all).

The ionized gas is
electrically conductive and current keeps flowing through it from one
end of the bulb to the other, keeping it ionized. (At that point you
could probably remove the fixture ground wire and it'd stay lit fine
'till you switched it off.)

True!

The ionized gas emits ultraviolet light which excites the phosphor on
the inside of the glass and makes it flouresce white, much like an
ultraviolet "black light" will make certain inks and stuff glow
brightly. That's why they call them "flourescent" lights BTW.

True! But anyone trying to make the coating glow from a blacklight will
usually not get that to work - the phsophor coating in most fluorescent
bulbs works well from shortwave UV and not from the longwave UV from a
blacklight. And most "fluorescent style" blacklights are true fluorescent
lamps - they have a phosphor converting shortwave UV (UVC) to longwave UV
(UVA, and at wavelengths too long for suntanning). Any UVC passing
through the phosphor is well-blocked by the glass.

Actually in a fluorescent lamp, maybe about 20% of the light is visible
light (bluish) from the glowing low pressure mercury vapor and about 80%
is from the phosphor. In a compact fluorescent, it's more like 25-75 or
so. Very roughly!!!

Doubtlessly Don Klipstein can do a more elegant job of presenting this

Maybe not quite if I work 2 jobs and then get online after working 13
hours....

- Don Klipstein )