How often should you switch off a light bulb?

Keys

We are having a friendly money saving debate... One of us leaves light bulbs (standard 40w or 60w) on, arguing that it is cheaper to leave a bulb on than to switch it on and off and later to switch it back on and back off. The reasoning being that it is the switching on of a bulb that uses the most electricity. The second party doesn't believe that is the case and is careful to switch the lights on and off as they go. Has anyone any idea which is the better money saving route, and at what point (leaving a light on for 5 mins, 10 mins etc) does it become cheaper to switch off. Thanks

penrhyn

The only argument that applies in this case is that the more you switch the light on and off the earlier it will fail. A standard filament bulb has very little switch on surge.
Why are you using these bulbs anyway, and 11 watt cfl would be appropriate if you want to leave the light on for long periods.

davetrousers

Many moons ago (before low energy bulbs were readily available) I did hear that for fluorescent lighting (tubes) that turning them on used about as much electricity as them being on for 20 minutes, so if you were going to leave the room for 5 minutes it would be more economical to leave them on. The accuracy of this I can't be sure.

However this does not apply to normal (old fashioned) light bulbs of the 40 or 60 watt type of which you speak.

alanwsg

There was a Mythbusters episode where they tested this one.

Outcome for normal (filament type) bulbs & LEDs, it's always worth switching them off.

For Fluorescent tubes, you save electricity by leaving them on only if you were intending to switch them off for 23 seconds or less.

However, frequent switching on/off shortened the lifetime of all types except LEDs (but they did switch them on/off continuously over several days!).

http://www.youtube.com/watch?v=2oo_EGODkrs

Keys

Thank you for your really helpful replies - and speed of response. In an office I worked in we were told by an electrician that when we went out for lunch we were to leave the fluorescent lights on and only switch them off at night to save the company money. Although these were fluorescent tubes of course - and this was a while ago.

Just haven't found that low energy bulbs give sufficient light but will change a few more over this weekend. And I had never heard of Mythbusters - really enjoyed watching the link and so thank you for telling me about it. Thanks so much everyone.

davetrousers

alanwsg wrote: »

For Fluorescent tubes, you save electricity by leaving them on only if you were intending to switch them off for 23 seconds or less.

Well that knocks my 20 minutes into a cocked hat!

lovinituk

alanwsg wrote: »

There was a Mythbusters episode where they tested this one.

Good old Mythbusters - one of the best programmes on TV in my opinion although I do have a thing for Kari

jamesperrett

As I understand it, frequently switching of fluorescent lights will dramatically shorten their life which is possibly where the 20 minutes comes from. Frequent switching of standard incandescent bulbs may shorten their life slightly but nothing like as much as fluorescent bulbs. That's why I still have a standard bulb in the loo but CFL's or LED's as much as possible everywhere else.

James.

t0rt0ise

Keys wrote: »

Thank you for your really helpful replies - and speed of response. In an office I worked in we were told by an electrician that when we went out for lunch we were to leave the fluorescent lights on and only switch them off at night to save the company money. Although these were fluorescent tubes of course - and this was a while ago.

And while you were being told that we were having sensors fitted whereby if you sat still too long the light turned off. Very annoying it was.

new2012

if you sat still too long the light turned off. Very annoying it was.

I used to work in an office like that. We had competitions to see if we could sit still long enough to turn the light off, then when they went off we jumped up and started waving our arms about.

Big boss man just happened to walk in on us all waving our arms about one time.

The sensor mysteriously vanished one weekend.

C_Mababejive

electric light is much the same as gas central heating. Just leave it on all the time and your bills will be cheaper.

Also turn your taps on and let them run and then the water bill will be cheaper.