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Wednesday, 5 February 2020

Fluorescent lamp Construction & working

Fluorescent Lamp


Circuit Diagram of fluorescent Lamp
Circuit Diagram of fluorescent Lamp

Construction Of Fluorescent lamp

Following are the main construction parts of lamp.

1. Transparent Tube

  • It is in the form of long glass tube with phosphor coating on its inner surface.
  • It consists of two main electrodes made up of the tangstone filament coated with electron emitting material like berrium oxide and are placed at ends of the tube.
  • The consists small small amount of mercury with little quantity of argon gas at low pressure. When the temperature increases within the tube, mercury changes into vapour form. One capacitor is connected across the supply to improve the power factor of circuit.
2.Starter

  • It consists of two electrodes one is fixed and another is U shaped made of bimetalic strip.
  • The electrodes are sealed in a glass bulb which is filled with helium and hydrogen for cooling purpose and the another one capacitor is used to eliminate the radio interference developed due to the arc. The two starter electrodes are normally opened.
3.Choke

  • It is made up of high inductive coil it provides the necessary starting voltage and it limits the current during normal working of the lamp.

Working of Fluorescent Lamp

  • When the lamp is connected to single phase AC supply an arc is established in the starter. This arc heats the bimetallic strip so it bends and make contact with fixed electrode. Hence the lamp circuit is closed. Therefore high current flows through the circuit. 
  • When the starter electrode closes the arc extinguishes and the starter electrodes cool down. Therefore the bimetallic strip comes to normal state that is open. Hence the circuit current reduces to zero.
  • Now very high voltage is induced in the choke due to change in current through it.
  • This high voltage along with supply voltage is applied across electrodes in tube due to which an electric discharge takes place between the two electrodes, first through argon gas, due to theflow of current through argon gas heat is produced mercury into mercury vapour then the regular discharge takes place through the mercury vapour.
  • So here mercury vapour gives ultraviolet light which is converted into visible light by phosphor coating an inner surface of tube.

Advantages
  • Low power consumption compare to incandescent lamp.
  • Longer  life which is about 3 to 4 times that of incandescent lamp.
  • Efficiency is more so gives more light as compares to incandescent lamp.
  • Super quality of light (approaching a day light).
  • No warming up time is required as compared to other discharge lamps.
  • Different color lamps can be obtained by using different types of fluorescent powder.
  • Low heat radiation.
Disadvantages
  • Initial cost of lamp is more.
  • With fluctuation switching operations light reduces.
  • Voltage fluctuation affects its life.
  • This lamp produces radio interference.
  •  Fluctuating light output produces undesirable strobo-scopic effect. 

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