Working Principle of a Tube Light

Key learnings:
  • Tube Light Definition: A tube light is defined as a fluorescent lamp that operates on the principle of mercury vapor gas discharge to convert ultraviolet light into visible light through a phosphor coating.
  • Material Composition: The tube light includes electrodes, phosphor coating, mercury, argon gas, and other necessary structural elements to function effectively.
  • Fluorescent Lamp Working Principle: The working principle involves ionizing mercury vapor and argon to produce light, initiated by a voltage surge from a starter mechanism.
  • Role of the Starter: The starter’s purpose is to heat and bend a bimetallic strip to create an initial electrical path, which is crucial for the light’s operation.
  • Continuous Operation Process: Once started, the tube light maintains light emission through the continuous ionization of gas, with the starter becoming inactive.

What is Tube Light?

A tube light, also known as a fluorescent lamp, operates through a low-pressure mercury vapor discharge that converts ultraviolet rays into visible light using a phosphor coating inside the glass tube.

Material Used Inside the Tube Light

The materials used to build a tube light are given below.

  1. Filament coils as electrodes
  2. Phosphor coated glass bulb
  3. Mercury drop
  4. Inert gases (argon)
  5. Electrode shield
  6. End cap
  7. Glass stem
material used in fluorescent lamp

Auxiliary Electrical Components along with Tube Light

Tube lights cannot function directly from the power supply and require auxiliary components to operate effectively.

  • Ballast: It may be electromagnetic ballast or electronic ballast.
  • Starter: The starter is a small neon glow up lamp that contains a fixed contact, a bimetallic strip and a small capacitor.
auxiliary electrical components along with tube light

Working Principle of Tube Light

  • 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.
  • The gas inside the starter ionizes under high voltage, heating and bending the bimetallic strip to make contact and allow current flow. Despite neon’s higher ionization potential than argon, the small electrode gap in the neon bulb enables an initial glow discharge.
  • 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.
  • When mercury atoms are discharged, they emit ultraviolet radiation that excites the phosphor coating inside the tube, producing visible light.
  • Starter gets inactive during operation of tube light.
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