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VK3ABK > LIGHTS 17.12.04 05:04l 66 Lines 3625 Bytes #999 (0) @ WW
BID : 33455_VK3KAY
Read: GUEST
Subj: Re: Fluroescent Lights again.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0BEL<TU5EX<7M3TJZ<SP7MGD<VK7AX<VK3AC<
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Sent: 041217/0217Z @:VK3KAY.#WEV.VIC.AUS.OC #:33455 [Wendouree] $:33455_VK3KAY
From: VK3ABK@VK3KAY.#WEV.VIC.AUS.OC
To : LIGHTS@WW
Hello again Unlit ones.
There is 'confusion' in my 'Fluroescent lights' bulletin. The bimetalic
strip 'switch' in the starter is 'open' before the main switch is closed.
The 'glow' discharge (ionized gas) in the starter causes the contacts to
close and the circuit is completed via the two heaters in the fluro'. In the
time it takes for the starter bimetalic strip to cool, and open the contacts,
the heated 'cathodes' in the fluro' will be (we hope!) emitting electrons.
The action of opening the starter contacts, causes a high voltage back-EMF
to appear between the fluro' tube heaters which should be still be 'hot'.
The resultant flow of ions and electrons through the fluro' then becomes
a 'short' across the starter which prevents further glow discharge.
All of this depends on the correct action of several 'components' which is
often a bit much to ask! So, we get a flicker-type start up that can be a
nuisance. Some help was found years ago in using a metalic strip along the
outside of the fluro' tube, which connected the metal end caps and somehow
caused a more reliable start up. These were called 'Instant Start' tubes
and may have prevented voltages on the tube surface reacting against the
'striking' of the tube. Some other improvements must have made this method
obsolete, as it's not done today.
Over night, I had a think about fluroescent lighting and the coating on the
inside surface of the tube. This coating 'fluroesces' due to the electrons
striking and releasing photons which then emit a characteristic colour which
depends on 'doping' of the base coating. I think it is, or was, Barium Oxide
which much later was found to be toxic. This is interesting, as I used to see
dud fluro' tubes didposed of by smashing them into a rubbish bin. Clouds of
'dust' would waft about the 'smasher', and all who watched with glee!
I understand that the gas used in the fluro' tube is no longer Mercury based
as this has now been found to be dangerous and a non-selling point. I thought
that a mixture of Neon and Argon was used in the early days, but this may be
wrong. I have had no experience with modern electronic fluro' lighting, so if
the question of a 'transformer' was about these, and how they operate, I would
like to hear more!
Incidently, there has been a TV series on the life of Nikola Tesla, in which
he was shown demonstrating his high voltage generator. He was shown using a
fluorescent tube that looked like our modern tubes, but I believe this was a
convenient misuse by the series director. The tubes that I saw being used in
the war years were 'experimental' then, and would not have been available in
Tesla's demonstration days. Tesla may have used a length of Neon tube which
goes back to the early days of electric signs and other commercial lighting.
My 'experimental tubes' were installed in an engineering drawing office, where
the draftsmen were having trouble drawing and lettering straight lines due to
as they claimed, the 100Hz 'flicker' from the high voltage neon tube lighting
that was common at the time. Fluroescent fittings using two tubes, with two
balast chokes of different inductance tended to smooth out the 100Hz flicker.
These 'early' fluros were unreliable, and I remember seeing the date marked
on the tubes as they were installed, and then when they failed. Only months,
and in some cases, days, elapsed between 'in and out'!
Well, enough tkinking back. I'm starting to get like Ian from Nelson in cold
wintery NW England. :-) . It's a lot of interesting stuff, Ian, keep it up!
73. Dick. VK3ABK.
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