Re: fluorescent lamp operating voltage
- From: Victor Roberts <xxx@xxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 07 Feb 2006 19:39:52 -0500
On 7 Feb 2006 14:51:36 GMT, phil-news-nospam@xxxxxxxx wrote:
I was reading about the voltage at which a fluorescent bulb's gas would
break down electrically, allowing full current to flow (as limited by the
ballast). It was mentioned that an 8 foot tube would have a breakdown
voltage of about 600 volts. Does that vary lineraly with length such that
a 4 foot tube would breakdown around 300 volts, and a 2 foot tube would do
so at around 150 volts?
If you are talking about instant start lamps or cold cathode
lamps AND if the lamp were mounted in free space with no
ground plane closer to the lamp than perhaps 5x the length
of the lamp, then perhaps.
However, in the real world the warm electrodes of rapid
start or switch start lamps control starting and even with
cold electrodes as in instant start lamps or cold cathode
lamps (which are different after they start but have similar
breakdown characteristics) the breakdown starts between the
electrodes and the nearest ground plane, since the ground
plane is closer than the electrode at the far end of the
lamp. This means that the breakdown voltage for instant
start or cold cathode lamps does not scale linearly with the
distance between the electrodes.
I'm curious if it is possible to operate a fluorescent bulb directly at a
voltage above the gas breakdown voltage, still current limited by a ballast
(magnetic or electronic), and not need a starter at all? It seems to me
that this should be possible since apparently neon tube lighting operates
that way, though at much higher voltages due to either the gas or the longer
tubes. I read quite a while ago that the neon light transformer also acts
as the current limiter. Can a transformer with suitable secondary voltage
and suitable short circuit current limit, operate a fluorescent bulb in a
direct way?
This is very common the North America. All Instant Start
lamps operate this way and even Rapid Start lamps use a
transformer with a built-in inductor, a so-called "leaky"
transformer.
If it can, what reasons would make this an uncommon practice?
It is not uncommon here. I believe that is the line voltage
is high enough to use a simple series choke, as it is in
Europe and ROW for lamps at least as long as four feet than
that system is less expensive than a leaky transformer.
I was reading stuff from the links at this web page:
http://nemesis.lonestar.org/reference/electricity/fluorescent/index.html
See the section on instant start.
--
Vic Roberts
http://www.RobertsResearchInc.com
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