Science Questions

Sat, 22nd Oct 2005

Part of the show Social Insects, Biting Bugs and a Potted History of Honey

Question

Simon in Tiptree asked:

Many years ago I was told that six foot fluorescent strip lights are more efficient and need less energy than tungsten lighting to run. Is this true? If so, how long do they have to be left on before they use less energy overall, so if you flicked on a light for a couple of seconds, would it be better to use the tungsten light bulb or the fluorescent light?

Answer

The way fluorescent lights work is that they contain gas at a certain low pressure, and you fire that gas up by putting a high frequency electrical signal through there. The electricity passing a current through the gas excites the atoms and they lose some of their electrons. The electrons are flicked up to a higher energy level, and then they fall back again to a normal energy level. When they do so, they emit some UV light, which strikes a phosphor, which is on the inside of the tube. That phosphor turns those UV rays into a second form of energy, which is visible white light. This process is very efficient. Tungsten light bulbs work by heating up a piece of metal in a tiny filament until it becomes white hot. Only about 20% of anything they actually use is turned into anything useful.

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