Working of Tubelight{Fluorescent lamp}

TubeLight

One of the most fascinating inventions 
of electronics/electrical world is the fluorescent lamp!. The working of tubelight itself is extraordinary.

Working : The tube light (old)  consists of a choke(G). ,Fluorescent tube(A) , D,C,E together is called a starter.B is the 230voltage supply with 50 Hz frequency (In india)

In order to start the lamp(on the tubelight) There should be a arc which has to struct in the fluorescent tube.For small lamps a very small voltage is required to start the arc and hence the lamp.However for large tubelights ,They need a large voltage(Around 1000 volts across the tube) to struct the arc(on the tubelight initially).

usual Doubt : The input supply is just 230volt ac supply.How to get 1000 volts?

Step 1 : Have you heard about inductor?. A choke is a coil of very large inductance and negligible resistance.In this circuit its denoted as G.

when we initially power the circuit(i.e on the button of the tubelight).A small current flows through the choke and the starter. There will be a glow discharge  in the starter.The starter consists of a bimetallic strip.The heat generated in the starter will make one of the contacts of bimetallic strip  to touch another metal.(coefficient of expansion of one of the metal is larger than the other).Thus the current will increase since a contact is made in the starter.Thus the two filaments (F) and a choke are in series to the supply voltage. as shown above .Now The voltage across tube is around 90v and its not at all sufficient to generate an arc.

Step 2: A good contact will not generate any heat.The Bimetallic strip which was made to connect in the first stage will break down.As we saw choke is in series with Filaments.So inductor current was flowing.Since the bimetallic strip in the starter is made to break/open(AUTOMATICALLY){It can be done even manually}. 

   diL/dt of the inductor becomes very large.(i.e during small duration the current falls down suddenly.That duration is breaking of the bimetallic strip)

we know that 

Voltage(Across inductor)=L diL/dt

The di/dt will be theoretically infinity.But in practically it will be very large.

So example VL(Acros choke) will be around 800volts.

The voltage across choke will be around 800 volts. {- (left side of the choke )  +(right side of the choke)} polarity
So VB+VG=Vi+VL =230+800 =1030v will appear across the fluorescent tube. A arc will strike and tubelight gets on.

And after the initial strike which is generated by high voltage arc.it can later work on 90volts.The starter can be removed.

Main principle behind this  : Generate an inductor current,Make it flow in a circuit. Break the circuit in a starter. which interrupts the current flow in choke and the filaments.(As inductor resists the change in the current a high voltage is generated across the across the choke)V=L di/dt .Thus a arc is generated which gives a start needed for the tubelight.

Practical working ? :

You can try removing the starter after the tubelight is on.It will have no impact,But if you on the tubelight without a starter.It wont get on.

So this invention is based on some physics and a basic principle on inductor(Inductor resists the change in current)