Published: 10 December, 1998

Fluorescent light mystery solved at last

How does a fluorescent light bulb work?

A fluorescent lamp consists of a glass tube that is filled with mercury vapor at low pressure. The inside of the tube is coated with a phosphorous substance. Two coiled metal (tungsten) filaments are at each end of the tube. When an electric current flows through the filaments they start to get hot and glow (like a regular light bulb). When we apply a voltage between the two filaments and electrons get sucked from one filament to the other. While zipping through the tube, electrons crash into mercury atoms, which start to glow and send out ultra-violet (UV) light.

UV-light is very, very violet. Actually it is so violet that you can't see it, but you can get a sunburn from it. So on its own UV-light wouldn't make a useful lamp: that's why there is a phosphorous substance in the inside of the glass tube. When UV-light hits the phosphor atoms, they absorb the UV light and send out the white light that illuminates your room. The conversion of light from one type to another is called fluorescence, which gave the fluorescent lamp its name.

Fluorescent lights conserve energy. For the same amount of light they need less power than usual light bulbs. By the way, the funny shaped light bulbs made of bent glass tubes in the supermarket are actually fluorescent lamps. Please don't play and break fluorescent lamps: they contain chemicals that are poisonous. When disposing of a fluorescent lamp, you should call the Recycling Center!