Insight - How CFL works

CFL (Compact Fluorescent Lamp) converts electrical energy to radiant energy. They are energy efficient and use better technology as compared to conventional tube lights and bulbs. It has two components:

a) A glass tube filled with argon and mercury vapor & coated with a layer of fluorescent material.

b) An electronic ballast circuit

The ballast circuit takes a 220 V input from external power source and sends a current into the fluorescent tube as output. When power supply is given to the CFL, filament attached with the cathode heats up and emits electrons in the tube. This ionizes the argon and mercury vapor particles.

Fig. 1: Image of a 25-watt CFL

A 25 Watt CFL is shown in the above image.

Circuitry

Fig. 2: Circuit Layout for Electronic Ballast

The above image shows the circuit for electronic ballast. This circuit takes a 220 V input from external power source and sends a current into the fluorescent tube as output. We can divide the circuit in two parts. Supply section and starting circuit. Supply section contains a coil, fuse, a bridge rectifier using diodes and a filtering capacitor. Starting section includes a diode, a capacitor, resistance and DIAC (DIode for Alternating Current).

Fig. 3: Supply Section and Starting Circuit

A closer look to its component can be viewed in the image.

Wiring & Filament

Fig. 4: Cathode and Anode Terminals of Circuit

The circuit has two terminals – Cathode and Anode which are inserted into the ends of the fluorescent tube. When the power is supplied to the circuit, Cathode is heated enough to emit the electrons into the tube. These electrons travel through the tube and reach another end of the tube where they are received by anode.

Fig. 5: CFL Filament

A filament is shown in the above image, both end contains the same filaments.

Working: The tube is filled with Argon and mercury vapors. When power supply is given to the CFL, filament attached with the cathode heats up and emits electrons in the tube. This ionizes the argon and mercury vapor particles. The ionized particles emit ultra violet radiations which strike with the fluorescent layer of material coated on the tube. In turn, fluorescent material spread a white light which lights up the room.