How Fluorescent Tube Lights Work


How Fluorescent Tube Lights Work

What is Fluorescent Lamp?

A fluorescent lamp or a fluorescent tube is a low weight mercury vapour lamp that uses fluorescence to deliver visible light.

An electric current in the gas energizes mercury vapor which delivers ultraviolet radiation through discharge process which causes a phosphor coating of the lamp inner wall to radiate visible light. A fluorescent lamp changes over electrical vitality into useful light to a great deal more proficiently than incandescent lamps.

The normal luminous viability of fluorescent lighting frameworks is 50-100 lumens for every watt, which is a few times the adequacy of incandescent lamps with equivalent light yield.

What’s Inside a Fluorescent Tube Light?


  • fluorescent lamp basically consists of a long glass gas discharge tube. Its inner surface is coated with phosphorous and is filled with an inert gas, generally argon, with a trace of mercury.
  • The tube is then finally sealed at low pressure with two filament electrodes each at its both ends.
  • These electrode filaments are used to preheat the tube and initiate a rapid conduction of electrons between the two end electrodes. The process initially requires a relatively high amount of power.
  • The energy also converts some of the mercury from a liquid to a gas. Electrons then collide with the gaseous mercury atoms, increasing the amount of energy. As electrons return to their original energy level, they begin to release light. However, the light they emit is ultraviolet, and not visible to the naked eye, so another step needs to take place before we can see the light.
  • This is why the tube was coated with phosphorous. Phosphors will give off light when exposed to light. When exposed to the ultraviolet light, the particles emit a white light which we can see.
  • Once the conduction of electrons between the electrodes is complete, no more heating of the filaments is required and whole system works at a much lower current.

How Fluorescent lamp works?

fluorescent tube
fluorescent tube
    • When the switch is ON, full voltage will come across the tube light through ballast and fluorescent lamp starter. No discharge happens initially i.e. no lumen output from the lamp.
    • At that full voltage first the glow discharge is established in the starter. This is because the electrodes gap in the neon bulb of starter is much lesser than that of inside the fluorescent lamp.
    • Then gas inside the starter gets ionized due to this full voltage and heats the bimetallic strip that is caused to be bent to connect to the fixed contact. Current starts flowing through the starter. Although the ionization potential of the neon is little bit more than that of the argon but still due to small electrode gap, high voltage gradient is appeared in the neon bulb and hence glow discharge is started first in starter.
    • As voltage gets reduced due to the current, causing a voltage drop across the inductor, the strip cools and breaks away from the fixed contact. At that moment a large L di/dt voltage surge comes across the inductor at the time of breaking.
    • This high valued surge comes across the tube light electrodes and strike penning mixture (mixture argon gas and mercury vapor).
    • Gas discharge process continues and current gets path to flow through the tube light gas only due to low resistance as compared to resistance of starter.
    • The discharge of mercury atoms produces ultraviolet radiation which in turn excites the phosphor powder coating to radiate visible light.
    • Starter gets inactive during operation of tube light.