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Light bulbs and energy saving

I've been wondering recently about how energy-efficient it is to switch off a light when you know you're going to switch it back on in only a few minutes' time (e.g. because you are only popping out of the room to go to the loo), and also how much the situation varies depending on what type of light you are using.

Googling produced a few results, which is a start, although they don't seem entirely authoritative to me. So I'm reporting back on my findings here, a) in case anyone else has been wondering about the same issue, and b) in the hope that someone can point me towards more detailed and convincing information on the subject.

According to this page, the initial surge in an ordinary incandescent household light bulb "would probably burn up one-tenth of a second's worth of regular electric light burning - or maybe a second, absolute maximum". So in other words, you may as well turn off an ordinary bulb even if you know you'll be switching it back on in five minutes' time.

Regarding fluorescent lights (which are what I have in my office at work), The University of Alberta has apparently recently been trying to encourage its staff to save energy by turning off unused lights. They say, "Turning fluor(e)scent lights off and on causes some wear. Studies show that if you turn them off and on in periods of less than 20 minutes it reduces the beneficial effects. Incandescent lights - more common in homes and on desktops -- can be switched off even if the space is vacant for less than 20 minutes."

This, of course, is a slightly different issue - they are really talking about the life-time of the fluorescent tubes, not how much energy they use while being switched on as compared to while running normally. But I guess they must take up a fair amount of energy when they are produced in the first place, so conserving the tubes themselves is worth thinking about - although I would really like to know how the two things play off against one another. And of course the University of Alberta offer no link or reference to whatever 'studies' they are talking about.

Meanwhile, on the same issue the University of Virginia's 'How Things Work' page reckons by a much shorter time-frame: "Since turning an incandescent bulb on and off doesn't shorten the life of its filament significantly, you do well to turn it off whenever possible. The same isn't true of a fluorescent tube--turning it on ages its filaments significantly (due to sputtering processes) so you shouldn't turn a fluorescent lamp off if you plan to restart it in less than about 1 minute."

One minute? Twenty minutes? Those are quite different lengths of time! I guess either way my office lights are probably best left on while I'm nipping out to the loo or to pick something up from the staff room. But, as I say, it would be handy to have a more authoritative guide than this.


( 27 comments — Leave a comment )
Feb. 23rd, 2007 10:24 am (UTC)
On a related theme, do you happen to know where I can get energy-saving bulbs that will not offend the aesthetic sensibilities of the person who is helping me with my DIY? I very much want energy-saving bulbs in my living room, and you would think there would not be a problem with this because it is my living room, but he is making a fuss about it and saying that it is no good putting up a nice light fitting if I am going to put ugly bulbs in it. I don't happen to believe they are ugly, and in any case nobody stares at a light bulb, but in order to avoid a major argument it would be nice to find a compromise if possible.
Feb. 23rd, 2007 10:26 am (UTC)
You can get the energy saving ones in all kinds of shapes- some that look just like a standard pearl filament bulb might not upset them.

Or use bigger lampshades so you can't see them :)
Feb. 23rd, 2007 10:37 am (UTC)
Thanks - I'll have a look. :-)
Feb. 23rd, 2007 10:41 am (UTC)
Try IKEA :)

I've got loads of that type of bulb, because my house is a converted bungalow, but unfortunately they didn't add a second lighting circuit to the fusebox. So if you have 60W filament bulbs and turn on more than one floor's worth, it blows the fuse. Hence we replaced all the bulbs (bar a couple in the kitchen) with the energy-efficient ones.

Even my garage has low power fluorescent tubes. Though I have to admit it's not as bright in there as I'd like!
Feb. 23rd, 2007 10:53 am (UTC)
I got some in Homebase which look like normal bulbs. Oddly they sold a 3 pack for £8.99, and a two pack for £8.99.

No, I couldn't work it out either.
Feb. 23rd, 2007 10:56 am (UTC)

I saw a similar piece of oddness recently, but I can't remember exactly what it was. :-)
Feb. 23rd, 2007 11:06 am (UTC)
I have no idea - but luckily it looks like I have friends who do!
Feb. 23rd, 2007 10:24 am (UTC)
It all changes again when you look at the energy efficient mini-fluorescent type bulbs that use electronics to control them (ie the sort that can be used as direct replacements for filament type ones). They're much softer at starting up, but have the downside of taking a minute or so to reach their full brightness as a result.

Also modern fluorescent tubes have more sophisticated starter circuits than the old fashioned ballast coil, so turning them on isn't so detrimental.

But you have to be aware when searching US based websites, that there's no real culture of trying to save energy, so things can be a bit vague. The best place to look might be Dutch or German sites if you can find any on the subject.
Feb. 23rd, 2007 11:09 am (UTC)
The trouble is that I don't speak Dutch or German! I was Googling using English-language terms, and those pages were the best I could find.
Feb. 23rd, 2007 11:11 am (UTC)
Maybe try Italian sites then. Or Roman Latin ones ;)
Feb. 23rd, 2007 10:37 am (UTC)
Argh! I thought I'd seen the last of that baby sun from Teletubbies :-(

Feb. 23rd, 2007 11:10 am (UTC)
Everything about the Teletubbies was scary, though Barney was far far worse.
Feb. 23rd, 2007 11:28 am (UTC)
not as bad as the Boobahs though. They're terrifying...
Feb. 23rd, 2007 11:50 am (UTC)
And the Tweenies! They make me feel physically ill with their stupid 'we have learning difficulties' voices.
Feb. 23rd, 2007 11:55 am (UTC)
Ah, poor Jakey, he's only likkle.


I know what you mean. As you can imagine, CBeebies plays a large role in our house, but there are some bits which I have trouble watching. Lots of it is fine, and some of the programmes are really good...
Feb. 23rd, 2007 01:47 pm (UTC)
Yet another good reason for not having a digibox... or an ariel...

Baby K is raising herself on Anime DVDs... She switches on the player and the TV, digs out the disc she wants and slips it into the machine... She still needs help with the menus, but that's OK...

Her personal favourites at the moment are Love Hina, Serial Experiments Lain and Trigun... I'm trying to convince her to try a broader range, but she's happy to stick to what she knows...

She's also very keen on Shrek, and Pixar movies...
Feb. 23rd, 2007 12:35 pm (UTC)
Ah yes, I know of Boobah, they should've retitled the show as "Reasons why tv show writers shouldn't take lsd", it was truly odd.
Feb. 23rd, 2007 11:12 am (UTC)
Aww, but I luuuurrrve him!!! He is so cute and surreal, and like a CGI Helios Everyone must worship him!
Feb. 23rd, 2007 01:45 pm (UTC)
He's not cute, he's evil! EVIL, I tell you!
Feb. 23rd, 2007 11:16 am (UTC)
I think a few minutes won't make that much of a difference in the long run, though having said that, as a force of habit I do switch off the light in a room after I walk out of it.

There are some offices where motiin sensors have been installed that switch the lights off if they don't detect anyone moving in them after something like five minutes.
Feb. 23rd, 2007 01:31 pm (UTC)
I hate those motion sensors, I worked in an office that had one, and it kept plunging me into darkness as I was typing.

As for the fluorescents that get brighter slowly, they are fantastic!
Feb. 23rd, 2007 01:43 pm (UTC)
It depends on the type. Those who have a pre-heater function (alas, can't remember the correct expression in english right now) are damaged in the long run by switching them off and on with less than 15 minutes inbetween. Those who don't preheat are not damaged by this.
Regarding the major energy consumption through switching on/off, this is truly minimal and irrelevant.
I have the scientific details about this somewhere (energy saving lightbulbs and switching on/off lights are part of the criteria for the eu ecolabel, after all..) but I'm not on my computer right now. As soon as I find the stuff, I'll send it to you.
Feb. 23rd, 2007 09:54 pm (UTC)
Don't go to any trouble, but if it's easy for you then, yes - that would be great.
Feb. 23rd, 2007 09:45 pm (UTC)
Most, but not all, of the bulbs in my house are energy-efficient. Unfortunately nearly all of these are several years old and are the type that take a while to warm up - the newest couple I have are much better in this regard. I have some sympathy with the campaigns to ban traditional light bulbs, but wonder whether they have considered all the consequences, given the number of shades and fittings where even the newer bulbs are just too big to fit properly. That's a lot of landfill.

Not that any of that answers your question but I've wanted to get something along those lines off my chest for some time ...
Feb. 23rd, 2007 09:56 pm (UTC)
That's a good point! It sounds from some of the things people have been suggesting above like manufacturers are moving more towards ones which are similar to traditional light-bulbs in terms of both performance and appearance, though.
Feb. 24th, 2007 09:56 am (UTC)
... turning an incandescent bulb on and off doesn't shorten the life of its filament significantly

In my experience incandescent bulbs almost always die as they are turned on, so I find this report difficult to believe.
Feb. 24th, 2007 12:44 pm (UTC)
Yes, indeed. But I am reasonably convinced by the first page I cited that it doesn't result in a vast wastage of energy, which was the main thing I was wondering about.
( 27 comments — Leave a comment )

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