Working of tube light

The tube light has three important parts:

• 1.       Tube (containing 2 filaments + vapour +  mercury gas)


• 2.       Ballast


• 3.       Starter
•  

The tube light has the filaments connected in series with the starter and ballast. The current flows through the circuit while the ends of the bimetallic strips in the starter are in contact. This warms up the tungsten filament. It starts emitting electron. The alternating nature of the input current leads growing and shrinking of the voltage across the ballast. This induces voltage spikes across the filaments which helps in movement of ions from cathode to anode.

By now the starter bimetallic strip gets heated due to the flow of current and opens up and get disconnected. The current now has a low resistance path through the mercury discharge tube. The resistance of the gas keeps on falling with increase in temperature. As a result the current through the tube goes on increasing and the tube light glows brighter. But if the current through the tube is not limited the tube will break. Here comes the role of ballast which now acts as current limiter thus preventing such accidents.

Some common doubts

Why does the tube light does not glow at once while using magnetic ballast?

• Because of wrong timing. The collapse in the magnetic field was not at the peak

What will happen if starter is connected to a bulb?

• It will glow alternately(blink).

What if the tube light is connected to a dc supply?

• The ballast will not function. As a result the rise in current will cause the tube to break.

How does tube light produce white light?

• The vaporized mercury produces UV radiation which when falls upon the phosphorous coating on the tube produces white light.

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