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Saving energy

#1 User is offline   jdonn 

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Posted 2009-February-24, 13:29

I was just told by a few people, quite adamantly, that turning off a lightbulb if you are leaving for an hour or so actually uses more energy (and costs more on your power bill) than simply leaving it on. Can anyone confirm that is either true or false, and maybe find me a good internet source?
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#2 User is online   helene_t 

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Posted 2009-February-24, 13:34

May be true for low0energy bulps in the sense that they burn out quicker if switch on/off often. But it doesn't cost more electricity. Sorry I don't believe it.
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#3 User is offline   P_Marlowe 

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Posted 2009-February-24, 13:57

Hi,

1h is too long, there will be a break even point, but after
1h you certainly have passed this point.

Assuming you have enery saving bulp, there is phase in the
beginning, when the bulb emmits more and more light.
I would say, that the enery efficiency at this point in time is
not very good, but I may of couse be wrong.

Assuming a classical bulb: The question is, what is the difference
between the beginning and the sitiuation after 1h.
The only difference I can see is the heat, and the heat of the
small wire should reach the max. temperature a lot earlier than
after an hour.

With kind regards
Marlowe
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Uwe Gebhardt (P_Marlowe)
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#4 User is offline   Aberlour10 

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Posted 2009-February-24, 14:01

Statistics say that electricity used for lighting = only 8-10% of entire e-power consumption in the avarage household. The real saving potential is in other areas. Two years ago I started to search in internet for such informations and tried to realize it at home. It was quite successfull, the e-power consuption in my 2 person-houshold lowered form +- 3300 kWh/year to about 2800 last year. My english is not good enough to go into details, but it's really easy to find these infos in internet.

Robert
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#5 User is offline   jdonn 

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Posted 2009-February-24, 14:03

I don't mind an interesting discussion being thrown in, but I'm looking for an answer specifically to the question I asked, that is a fact and not just an opinion (I have plenty of those already!) Please assume regular or old fashioned light bulbs, not the energy efficient ones. Thanks.
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#6 User is online   helene_t 

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Posted 2009-February-24, 14:12

you get plenty of answers when googling for example
"light bulb" "turning on" energy
The break-even Uwe talks about appears to be less than a second.

That is a little surprising since I would expect wolfram to have positive resistance-termerature coefficient and therefor use more energy until it has reached it equilibrium temperature.

But it appears to be an urban legend.
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#7 User is offline   akhare 

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Posted 2009-February-24, 14:18

http://apps1.eere.energy.gov/consumer/your...m/mytopic=12280

Incandescent lights (or bulbs) should be turned off whenever they are not needed. Nearly all types of incandescent light bulbs are fairly inexpensive to produce and are relatively inefficient. Only about 10%–15% of the electricity that incandescent lights consume results in light—the rest is turned into heat. Turning the light(s) off will keep a room cooler, an extra benefit in the summer. Therefore, the value of the energy saved by not having the lights on will be far greater than the cost of having to replace the bulb.


The cost effectiveness of turning fluorescent lights off to conserve energy is a bit more complicated. For most areas of the United States, a general rule-of-thumb for when to turn off a fluorescent light is if you leave a room for more than 15 minutes, it is probably more cost effective to turn the light off. Or in other words, if you leave the room for only up to 15 minutes, it will generally be more cost effective to leave the light(s) on.
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#8 User is offline   P_Marlowe 

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Posted 2009-February-24, 14:27

Hi,

A discussion (in german) you can find here.
http://www.gutefrage.net/frage/wie-hoch-is...ten-einer-lampe

Basically (short summary):
The power is linear depend from the time, only at the beginning there is short
time intervall, which leads to a higher power consumption because of higer
voltage.
This is basic physics, every college book will tell you this.

So turning of the light even for seconds saves energy, but may reduce the
lifetime of the bulb.
So if you take into account the enery needed for producing the bulb than it
makes sense to not turning of the light for a short period of time.

Of course this is not a official internet source, I searched the net, but could
not find a better side.

With kind regards
Marlowe
With kind regards
Uwe Gebhardt (P_Marlowe)
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#9 User is offline   jdonn 

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Posted 2009-February-24, 14:50

helene_t, on Feb 24 2009, 03:12 PM, said:

you get plenty of answers when googling for example
"light bulb" "turning on" energy
The break-even Uwe talks about appears to be less than a second.

That is a little surprising since I would expect wolfram to have positive resistance-termerature coefficient and therefor use more energy until it has reached it equilibrium temperature.

But it appears to be an urban legend.

I found it hard to google since all I found were articles about energy efficient light bulbs. That's why I enlist the help of my googling minions on the forums. :)

Edit: Ok thanks Helene, your google let me find mythbusters episode 69
http://mythbustersre...s.com/episode69
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#10 User is offline   Echognome 

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Posted 2009-February-24, 15:11

Darn. I was going to mention the Mythbusters episode, since I saw that one. I remember that they had it setup where they turned the lights off and on for like two weeks straight. Only one lightbulb still worked after all that. I can't remember the brand.
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#11 User is offline   Al_U_Card 

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Posted 2009-February-24, 15:12

So what if the bulb falls 22,000 feet and lands on a bomb while it is off? :)
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#12 User is offline   jdonn 

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Posted 2009-February-24, 15:17

Echognome, on Feb 24 2009, 04:11 PM, said:

Darn. I was going to mention the Mythbusters episode, since I saw that one. I remember that they had it setup where they turned the lights off and on for like two weeks straight. Only one lightbulb still worked after all that. I can't remember the brand.

I just had the following enlightening conversation with one of the urban legend spreaders who prompted this thread.

ULS: But I know it's better to leave a heater on than to turn it off and on again in a short period of time.
JSD: Of course it uses more energy to heat a cold room than to keep a hot room hot. But it does not use more energy to lighten a dark room than to keep a light room light.
ULS: Huh?
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#13 User is offline   TimG 

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Posted 2009-February-24, 15:25

Sorry I don't have reference, but I think this myth was true for early generation florescent lights.
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#14 User is offline   kenrexford 

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Posted 2009-February-24, 22:26

jdonn, on Feb 24 2009, 02:29 PM, said:

I was just told by a few people, quite adamantly, that turning off a lightbulb if you are leaving for an hour or so actually uses more energy (and costs more on your power bill) than simply leaving it on. Can anyone confirm that is either true or false, and maybe find me a good internet source?

I suppose one needs to also determine to what energy you are referring. For, it takes a bit of personal energy to actually turn off the lightbulb.

First, you have the simple manual task of actually flipping the switch. Depending on the location of the lightbulb, you might also need to walk to the lightbulb. Those physical actions consume energy, which you must replace by consuming food. That food was grown, packaged, cooked, and consumed, all of which consumed energy that would not need to be replaced if you did not go about the added task of turning off the lightbulb. But, against that is the energy consumed doing whatever you would be doing instead of going about the task of turning out the lightbulb. Maybe that would have been spending ever-so-little extra time consuming beer. But, that slight increment might mean that you actually sleep longer when you get home. Or, you might have just enough extra to get drunk and forget to turn off the light when you pass out, which really throws everything off. There must be some minor impact on your likelihood of getting drunk enough to leave the lights on, and this should be considered.

Second, actually remembering to turn off the light consumes brain energy. That also must be fed, with all of the aforementioned costs. Moreover, by dedicating a portion of your thought processes to turning off lights when you leave, you may find that you forget other things, like protection for the evening festivities. Then, on that rare occasion where the alcohol does not lead to passing out at home but rather passing out in some strange person's home, and perhaps leaving their lights on, you might actually have the misfortune of adding to the carbon footprints of the community by addition of a screaming new consumer. This would be very bad, as these critters leave lights on all over the place, further consuming energy.

Third, by turning off the lights, you increase the likelihood that the screaming new consumers resulting from last generation's failed energy conservation efforts might find better cause to enter your abode while you are away at the aforementioned bar. The result of this, although not actually involving lights in your house at that moment, may be the incurring of many colored lights outside of your home, lights that are supplied with power generated by crusiers of our local finest. That light, and those bulbs, run off of the most inefficient of power sources, gasoline, and are undoubtedly much more costly than the initial light bulb and its energy consumption. All of this leads you, undoubtedly, to then leave your lights on even more than before, perhaps even with massive high-power lights that are triggered by motion occurring in your yard, which could be from benign sources like squirrels, raccoons, and the frolicking of the aforementioned screaming new consumers.

In light of all of this, my suggestion is to just leave the lights on.
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#15 User is online   matmat 

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Posted 2009-February-25, 01:37

jdonn, on Feb 24 2009, 04:17 PM, said:

Echognome, on Feb 24 2009, 04:11 PM, said:

Darn.  I was going to mention the Mythbusters episode, since I saw that one.  I remember that they had it setup where they turned the lights off and on for like two weeks straight.  Only one lightbulb still worked after all that.  I can't remember the brand.

I just had the following enlightening conversation with one of the urban legend spreaders who prompted this thread.

ULS: But I know it's better to leave a heater on than to turn it off and on again in a short period of time.
JSD: Of course it uses more energy to heat a cold room than to keep a hot room hot. But it does not use more energy to lighten a dark room than to keep a light room light.
ULS: Huh?


hmmm
unless of course you're using the light bulb to heat the room
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#16 User is online   matmat 

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Posted 2009-February-25, 01:45

kenrexford, on Feb 24 2009, 11:26 PM, said:

First, you have the simple manual task of actually flipping the switch.  Depending on the location of the lightbulb, you might also need to walk to the lightbulb.

did you miss the XXth century? there is this device, called a CLAPPER.

and this...

Quote

In light of all of this, my suggestion is to just leave the lights on.


...this is really bad.
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#17 User is offline   mike777 

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Posted 2009-February-25, 02:29

I will let those on the forums to discuss the details.


I only vote for using more energy...MUCH more energy compared to the option using less.

I vote Kenberg to honest count.


edit: side note


I vote for thinking of communication, broadband in all phases(BBO) as an unlimited resource. I resource where the monetary value is close to zero/free.
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#18 User is online   helene_t 

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Posted 2009-February-25, 05:31

jdonn, on Feb 24 2009, 10:17 PM, said:

ULS: But I know it's better to leave a heater on than to turn it off and on again in a short period of time.

This is more obviously wrong that the lightbulb UL. An electric heater needs one joule of electricity to provide one joule of heat. It is as simple as that. Moreover, the amount of energy required to keep a house T degrees warmer than the surroundings is proportional to T. But of course it could be that turning it off and on reduces its lifespan.
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#19 User is offline   mike777 

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Posted 2009-February-25, 05:36

helene_t, on Feb 25 2009, 06:31 AM, said:

jdonn, on Feb 24 2009, 10:17 PM, said:

ULS: But I know it's better to leave a heater on than to turn it off and on again in a short period of time.

This is more obviously wrong that the lightbulb UL. An electric heater needs one joule of electricity to provide one joule of heat. It is as simple as that. Moreover, the amount of energy required to keep a house T degrees warmer than the surroundings is proportional to T. But of course it could be that turning it off and on reduces its lifespan.

Yes, I think some are saying one joule of heat from a home heater unit requires more than one joule of energy. think about it.
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#20 User is offline   Wackojack 

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Posted 2009-February-25, 06:51

When you turn on a filament light bulb from cold, the initial resistance of the filament is around one tenth of its resistance when at it operating temperature. This means that the instantaneous power it consumes when it is switched on is about 10 times that of its continuous power. However, it only takes milliseconds for the filament to warm to its operating resistance when the power it consumes is its rated power (give or take a small percentage variation proportional to the fluctuations in the mains voltage). Thus the transient extra power consumed declines to zero in a few milliseconds. So take a 100 watt lamp. Over 1 hour continuous it would consume 0.1 of unit or 360,000 watt seconds of electricity. From switch on, the extra energy consumed would be of the order of 360,010 watt seconds. Would you be paying for this extra 10 watt seconds on your electrcity bill? Well, if you leave the light on when you go out for an hour you spend an extra 360,000 watt-seconds in order to save 10 watt seconds. Your electricity meter wont see the extra 10 watt-seconds on switch on, but on switch-off it will have a small inertia which might amount to 10 watt-seconds. 10 watt-seconds btw is approx 0.0003 of a unit of electricity costing you 0.003 pence or say 0.004 cents. So you are spending an extra 1 cent at 10 cents a unit in order to save ).004 cents.

Whatever it cost you in more frequent replacement of light bulbs and extra personal energy consumed, you didn't want to know.
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