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How does a light bulb affect energy use?

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September 12, 2011 9:27PM

Like all electrical devices, light bulbs consume energy. Traditional (incandescent) light bulbs work by using electricity to heat a "filament" inside the bulb until it is so hot that it glows brightly, whereas newer "energy saving" bulbs use a different principle entirely (they are rather like a small "strip light" or "fluorescent light" such as are normally found in shops and offices etc)

To get the same amount of light, traditional bulbs use much more electrical energy than the newer type. You might think that this means that by using new-type "energy-saving" lighting you will obviously save energy (and hence reduce your utility bills), but it's not quite that simple. Most of the energy consumed by a traditional bulb goes to creating heat (you have probably noticed that they are too hot to touch). If you have, say, 4 60watt bulbs in your lounge, you are using 4 x 60 = 240 watts of electricity, of which almost all is being given off as heat and is therefore warming your lounge. If you replace these bulbs with low energy ones, that 240 watts of heating will be made up by your central heating system which will "trip on" the radiators, so you will burn extra gas to make up the lack of heating from the lights! So your gas consumption (and your gas bill) will go up as your electricity bill goes down.

This effect is most pronounced in winter, when you are likely to use more lights for a much longer time (because days are short) and less pronounced in summer - but you don't use lights or heating much in summer anyway.

So it's a complicated business, but the point is that if you buy energy-saving bulbs which claim to offer a saving of (say) 100 pounds a year, keep in mind that your gas bill will go up (although not necessarily by 100 pounds) - if you are using a very expensive form of heating you could find that your overall costs actually rise, although this is unlikely. You might well save some energy, but probably only a fraction of what most people expect, and of course most people see the reduced electricity bill and feel good, but don't notice the rise in gas consumption - or even if they do, they don't realise it's because of the new light bulbs!