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VK3ABK > LIGHTS 16.12.04 08:23l 56 Lines 2706 Bytes #999 (0) @ WW
BID : 33388_VK3KAY
Read: GUEST
Subj: Re: Fluroescent lights.
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0SM<DB0PKE<DB0GOS<ON0AR<ON0AR<ZL2BAU<
VK3AYM<VK3APC<VK3KAY
Sent: 041216/0546Z @:VK3KAY.#WEV.VIC.AUS.OC #:33388 [Wendouree] $:33388_VK3KAY
From: VK3ABK@VK3KAY.#WEV.VIC.AUS.OC
To : LIGHTS@WW
Hello Andy ZR2ACJ and all interested.
The question of how does a fluroescent light operate has been asked before
and John, G8MNY, among others have answered it. There may still be others
who are not sure and may get some inspiration from various explanations, so
to add to the confusion, here is my attempt from the days during WW2 when
I was first introduced to a fluroescent tube light fitting.
This is the circuit of an 'old fashioned' but still relevant, 'fluro'.
sw Choke/Balast
ÄÄ\ ÄÄÂÄÄ()()()()ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
AC ³ ÄÄÄÄÄÄÄÄ ³
ÄÁÄ ³ The fluroescent tube
Mains ÄÂÄ C Tube. ³ is filled with a gas
Voltage ³ showing Ionic discharge ³ Neon/Argon which is
ÄÄÄÄÄÄÁÄÄÄÄÄÄ¿ ---------------------- ÚÄÙ Ionized when the hot
H ÚÄÙ ---------------------- ÀÄ¿ H cathodes 'H' emit
³ Ú Ä Ä Ä ¿ ³ electrons.
A heater (filament)ÀÄÄÄÄÄÄÄÄÄÄÄÄÄo /ÄÄÄÄÄÄÄÄÄÄÄÄÙ
at each end of the tube À Ä Ä Ä Ù
enhances the electron The starter.
emission. A gas discharge tube
with bimetalic strip.
Before the mains switch is closed, the bimetalic contact in the starter is
closed. This completes a circuit from the mains voltage via the heaters.
The heaters 'heat' and the gas in the starter ionizes, causing the bimetalic
strip contact to open. By this time, the gas in the fluroescent tube should
have also ionized, and an electron flow will be maintained even though the
starter is no longer 'closed'. A 'high' voltage, due to back EMF caused by
the collapsing field in the choke supplies a 'starting' voltage between the
fluorescent tube heaters. Several starting cycles may be needed before the
tube lights, hence the flicker that usually occurs at switch on. The flow
of current throught the fluro' effectively shorts out the starter, and the
bimetalic heating is not repeated. A dud starter will upset that theory. :-(
The choke serves as a current limiter, not only when the tube is lit, but
also to act as a surge protector to limit inrush current at switch on.
Capacitor C is 'sometimes' included to help correct the laging power factor
due to the choke inductance. Cheap light fittings may not do this.
Yes, it may be old fashioned, and electronic starting is with us; but for
cost and simplicity, the 'original' is still selling like 'hot cakes'!
I think we have answered all Andy's questions.
73. Dick. VK3ABK.
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