Working Principle of a Tube Light

What is tube light?

Tube shaped florescent lamp is termed as tube light. Tube light is a lamp that works on low pressure mercury vapor discharge phenomenon and converts ultra violate ray into visible ray with the help of phosphor coated inside 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

Auxiliary Electrical Components along with Tube Light

The tube light does not work directly on power supply. It needs some auxiliary components to work. They are-

• 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.

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.
• 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 causes 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 ultra violet radiation which in turn excites the phosphor powder coating to radiate visible light.
• Starter gets inactive during operation of tube light.