Saturday, 14 March 2009

Shedding some light. Maybe.


I thought I had left this urban myth behind long ago. I first met it in 1983 and re-met it over the weekend.

It goes like this: I don't turn lights off because it uses more power to turn them on and off than they use when on.

Really? I don't think so.

How much more? Lets say 100 times, for the argument. It's generous.

How long does it take to turn a light on? Let's say half a second, for the argument. It's generous.

100 times a half =50. It's generous. Squared.

So if you turn a light off for anything over a minute you will be saving more power than if you left it on. So turn it off, already.

And take that myth and bury it. Somewhere dark.


But a different question, same topic: It was suggested that the turning on and off of a power-saving fluorescent bulb shortens it's life and that, if you include the cost of the bulb, the economics can favour leaving it on. That complicates the calculation. I still don't like it though.

Anyone know about this?


  1. Once again... no clue. Stop asking questions, you... it's like playing Trivial Pursuit, when I realize how little I actually know!

  2. What would it be like for you if I didn't ask questions?

  3. Just give us facts and what you think. Because not knowing what to answer makes me look like a fool. But I AM a fool when it comes to things like this..ha! I just turn it off when the sunlight peeps in. Or when I need to sleep. No brainer. But makes my life simple. He he..saving electricity? How much can I save? Still have to pay's not like it can save hundreds of bucks. (Now I remember my parents had stickers saying SWITCH IT OFF on all our plugs and sockets when I was little)

  4. This reminds me of the kind of questions we got in school : if 1 tap fills a bath in 5 minutes, how much time will it take for 2 woodcutters to chop down 600 trees. I could never work those darn things out.

  5. I always turn the light off, it improves my looks.

  6. DOH, I do know that you cannot buy traditional 100 wat light bulbs in the UK. What puzzles me is where have they put them all.

  7. I thought the myth was (and I'm not convinced it's a myth) that switching off and on reduced the life of the bulb, whereas leaving it on doesn't put the filament under strain.

  8. You'd have to calculate the current used which surges through the starter mechanism before the tube strikes. A neon tube works rather like a miniature lightning storm. But first it needs a kick-start. Old strip lights had a plug-in starter (still do in many offices) which you could hear ticking as it heated up the bi-metallic switch. Then there's the heat wasted in the choke . . . life's too short, people.

  9. Blu, they are being phased out. I only just heard about this, although the UK goverment announced it in September 2007:

    "Plans to phase out the traditional lightbulb by 2011 have been announced by Environment Secretary Hilary Benn. ... Less powerful traditional bulbs would be taken off the shelves in stages under the voluntary energy-saving scheme by 2011."

    100w bulbs are already scarce where I am too.

  10. I think the myth came about because it takes more fuel to start a diesel locomotive after it has been idle for 8 hours in the cold than it would be to let it run those 8 hours. This is why when you pass by a train yard in the winter you see the trains running in the evening (spooky, but practical).

  11. So I've read the post and the ten comments and am still unenlightened (geddit?). I would really like to know though.

    We used to keep folding the laptop - which is our only computer - away when we weren't using it, but then started getting multiple blue screens, which are far fewer if we leave it running. We reckon the cost to ourselves and the environment is probably less that way than if we have to replace the computer. It puts itself on standby after a while anyway.


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