flouresent lighting
Jason Goga
In chemistry class the teacher was illustrating flouresent lighting, and explained that the charge caused the electrons to leap into higher energy levels, however not being able to sustain them they would fall back down realeasing energy as light. Now I was curious, I've never seen a flouresent light run from DC. so is it the constant returning to 0 volts that causes the electrons to fall back down or do they do so on their own accord?
-Jason
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* Origin: C.A. - FrontDoor (1:348/207)
Cyberman
Jason Goga was espousing about 'flouresent lighting',
on [10-08-92 21:11] to All!
JG> In chemistry class the teacher was illustrating flouresent lighting,
JG> and explained that the charge caused the electrons to leap into higher
JG> energy levels, however not being able to sustain them they would fall
JG> back down realeasing energy as light. Now I was curious, I've never
JG> seen a flouresent light run from DC. so is it the constant returning
JG> to 0 volts that causes the electrons to fall back down or do they do
JG> so on their own accord?
A flouresent lamp works this way:
A photon of UV wavelength stirkes the phosphorescent
coating on the tube (white stuff) the phosphor is
exciting to a higher state and then not being able to
maintain it losses a specific amount of energy and
returns to it's ground state. This produces a different
wavelength of light WHICH in fact is ussually lower.
The UV light is produced by a low preasure gas inside the
tube (I can't remember what they use). You can run a
fourescent of of high voltage DC. AC is used because
it's relatively common.
Stephen Cybe...@Toz.Buffalo.NY.US
Scripted at Sat 10-10-1992 16:06:22
... No sense being pessimistic. It wouldn't work anyway.
--- Blue Wave/QWK v2.10
Dave Pierson
>(Jason Goga) writes:
(inquiring about DC and fluorescent lamps)
The lamps are quite happy on DC, except.... With all the currrent flow
in one direction, the eletrodes "wear out" more quickly at one end.
Also, the tube "blackens" assymetrically.
Additionally, the easiest way to do the current limiting on DC is with a
reistor, which is more lossy than the ballast used (inductor) usable
with AC operation.
thanks
dave pierson |the facts, as accurately as i can manage,
Digital Equipment Corporation |the opinions, my own.
146 Main St |I am the NRA.
Maynard, Mass 01754 pie...@msd27.enet.dec.com
"He has read everything, and, to his credit, written nothing." A J Raffles
Kees van der Wal
(Jason Goga) writes:
> In chemistry class the teacher was illustrating flouresent lighting, and
> explained that the charge caused the electrons to leap into higher energy
> levels, however not being able to sustain them they would fall back down
> realeasing energy as light. Now I ...
[The original texts has been truncated here by the VMS editor because it sees
the entire paragraph as a single and too long line]
It's a 3-step process.
1) The high voltage between the ends of tube cause a stream of electrons
rushing from one end to the other.
2) The rushing electrons collide with the gas inside (Mercury?). The electrons
belonging to the gas are excited to higher energy levels. As this is an
unstable situation the electrons "fall down" to a stable position, emitting a
foton. This light is not very useful as it is very blue and contains a lot of
UV radiation.
3) The UV radiation hits the phosphor at the inside of the tube. I don't know
how it is done but a similar process in the phosphor "converts" the mainly
invisible radiation into visible and useful light. The type of phosphor
determines the colour of the light emitted by the tube.
Wheter the tube runs from DC or AC doesn't matter; it only has effect on the
first step. If the voltage is too low to operate a tube, the most common way is
to convert it to AC and use a transformer. There's no need for a rectifier
afterwards but I can seen no harm in using one.
Regards, <kees>
Martin McCormick
The question was asked as to whether a flourescent light would work on DC.
Yes, it would. The low-pressure mixture of Argon and Murkury vapor would
glow in UV, just fine, and there would be none of that flicker that people
notice, but getting the 750 volts or so to ionize the vapor mixture would
be a trick. You would either need lots of batteries or a DC/DC converter to do the job. Inside a DC/DC converter, one finds a chopper circuit and step-up
transformer, a rectifier diode or diodes, and a filter capacitor. In an
ordinary flourescent lamp, one finds an autotransformer called a ballast,
possibly a starter to apply heat to the cathodes at each end of the tube,
and the tube, itself. The flourescent tube is actually its own rectifier,
but each end of the tube takes turns being a cathod or annode depending upon
which way the polarity is going. Unless the flicker of the tube running
on AC was unacceptable, there would be no good reason to run one on DC.
Martin McCormick WB5AGZ Stillwater, OK
O.S.U. Computer Center Data Communications Group
ir...@yang.earlham.edu
> In article <71862...@mailbox.bison.mb>, Jason...@mailbox.bison.mb.ca
> (Jason Goga) writes:
>
>> In chemistry class the teacher was illustrating flouresent lighting, and
>
> 1) The high voltage between the ends of tube cause a stream of electrons
> rushing from one end to the other.
>
> 2) The rushing electrons collide with the gas inside (Mercury?). The electrons
> belonging to the gas are excited to higher energy levels. As this is an
> unstable situation the electrons "fall down" to a stable position, emitting a
> foton. This light is not very useful as it is very blue and contains a lot of
> UV radiation.
>
> 3) The UV radiation hits the phosphor at the inside of the tube. I don't know
> how it is done but a similar process in the phosphor "converts" the mainly
> invisible radiation into visible and useful light. The type of phosphor
> determines the colour of the light emitted by the tube.
>
The UV radiation is of the correct engery to bring some of the electrons in the
phosphor up to a higher energy level. Then then bounce back down through a
different route of energy transistions emitting differnt frequency photons.
Here is a diagram.
4 _
4a -
3 _ 3a -
2a _
2 _
1 -
These are not at all acurate but lets say they are the energy level of the
atoms in the phosphor. The UV is high energy, short wavelenght high frequecy
light. It excites an electron in the 1 state up to the 4 state. This electron
can them come down in a couple of different ways. 4 to 4a 4 to 3a 4 to 3 4 to
2a 4 to 2. 4 to 1 would be forbidden. But it would come down in little jumps
emmiting lower energy photons each time. These lower energy photons would have
longer wavelengths... and lower frequencies. They would be, or some of them
would be in the visible spectrum.
This is how I understand it at least. The energy states are defined by the
possible configurations of the electrons that can be predicted with from
emirical data from Ryberg's eqautions or from theory with the SCH eqation. I
will not go into those because they make my brain hurt even though I am
supposed to know them.
>
> Regards, <kees>
--
-ira
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