How Compact Fluorescent Bulbs & Tubes work?

Answer

Unlike traditional filament bulbs, compact fluorescent bulbs & tubes do not rely on a metal filament to create light. The majority of the light output is generated from a phosphor coating by the process of fluorescence.

A CFL consists of a sealed glass tube with a heating cathode at each end. The inside of the glass tube is coated with a phosphor powder (by changing the colour of the powder it is possible to get different colour light from the tube, such as warm light and daylight). The sealed tube consists of an inert gas such as argon or krypton at very low pressure (these gases are both found in the air around us) and a very small amount of mercury.

To light the tube a current is passed through the heating cathodes for a short time and then a large voltage is applied between the two cathodes. Electrons fly up and down the tube colliding with atoms of mercury vapour in the tube. This in turn excites the phosphor coating on the inside of the tube and light is produced!

An extremely small amount of cathode is used up each time the bulb or tube is switched on. Once the cathode is used up the tube will not light (this is seen as black sections at the end of the tube and often accompanied by flashing at either end). Once the tube has reached this state it should be replaced. The more times a fluorescent bulb or tube is switched on & off the shorter it’s life will be.