Turn Out The Lights – Or Not?


Funny how this is still an issue today when 40 years ago parents were telling their children to do the same to save money. I think of it now because I recently noticed that some people, when leaving an area, leaves the lights on. The reason given for leaving the lights on is that they “are going right back”. I got to thinking about whether my claim that they should “turn off the lights” holds up to examination.

If the math is done on the length of time the lights are on, you can see that turning off the lights even if you do return soon will save big, percentage-wise. Calculate in the fact that often “going right back through” turns into 10, 20, or even 30 minutes and the percentage savings are huge. For example, assume it takes about 20 or 30 seconds to walk through a room and hall area. This is from turning on the lights at one end until you reach the switch at the other end. If we assume 1/2 minute to transverse the area, then the lights need to be on for 30 seconds. If they are left on because “I am going right back”, and right back is just 5 minutes, then the lights are on for 10 times longer than is necessary. If a distraction arises, the lights might stay on for 20 minutes, 40 times longer, waiting for the return trip.

As can be seen, turning off a light when you leave an area can save a big percentage of electricity. The real question, though, is what is being saved. Energy, yes, and especially when you multiply this by millions of people, the energy savings can be huge. But do you save money? This is a harder thing to determine. Since supposedly every time a light is turned on, the life span of the bulb is reduced, is it possible that a person who is constantly turning lights off and on may pay more than the savings in energy costs to replace light bulbs? I don’t think this has been looked at, but it certainly seems reasonable.

The other side of this could be the argument that saving energy is more important than being able to purchase a few less light bulbs every year. I am not sure this is valid either because every light bulb has energy and pollution costs associated with its manufacture, and environmental costs associated with its disposal. The more light bulbs you go through, the higher your contribution to this cost. The manufacture and disposal costs are particularly high for fluorescent bulbs.

This is a question that could eventually be answered when the new LED lights become more affordable and widely available. I have read that not only are these much more energy efficient and safer for the environment, but their life span is not much reduced by a large number of off and on cycles.

For now, what do you think? At what point does turning off lights make economic and environmental sense. What do you do and why?

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Will Sig
1 ender

the guys at mythbusters tackled this one. if i remember correctly, you’re still better off to turn lights off.


2 Will

Mythbusters eh! I like those folks. I’ll have to look it up on their site to see what variables they considered. Thanks!


3 Will

I found several references to the Mythbuster’s recommendation, but not their original episode. They seem to just conclude that you should turn out the lights because it is not hard on the light bulb. If that is true, why do mine always blow when I turn them on and never when already on?


4 JD Thomas

From what I have read, modern incandescent bulbs are less prone to deterioration from being turned on and off as compard to bulbs from 20 years ago.

For the money savings, take a look at this:

What about the costs : According to the CEC initial cost of an incandescent light bulb is about $0.50. Recent prices comparisons conducted in the Sacramento and Los Angeles areas found that CFL light bulbs were generally under $3.00 per bulb. However, a new 20-watt compact fluorescent light bulb produces as much light as a traditional 75-watt incandescent bulb. The CFL also lasts up to 10 times longer than a traditional incandescent light bulb (an incandescent bulb has a lamp life of 1,000 hours while a CFL has a lamp life of 10,000 hours). Bases on and average California energy costs of $.105 per kWh the total energy cost of a incandescent light vs. a CFL over the life of a CFL is $78.75 vs. $23.25 or a $55.50 energy savings. Combine the energy savings with the fact that one $3.00 CLF will replace 10 $0.50 incandescent bulbs and the total savings per bulb is $57.50.

From: http://info.sen.ca.gov/pub/07-08/bill/asm/ab_0701-0750/ab_722_cfa_20070423_094447_asm_comm.html


5 Will

Hi Techfun. I like the theme you are using on your site. Was it designed by Pragya just for you? I have been considering going to a cleaner looking theme, but because of all the customizations etc., like the way I have my sidebar, I want to be careful. I want to be sure I have a good one that will be supported through all the,(increasingly frequent), WordPress releases.

Thanks for the info and the link. I actually wrote a couple of recent posts about CFL’s. (Linked below) Looked at purely from a dollars standpoint, it is indeed a no-brainer. That is why I have changed 50% of the bulbs in our house. The ones I don’t change are the ones on table and floor lamps within reach of the kids. I am too worried about them getting broken. The other thing that is concerning is that common sense says that as the years go by and they need to be replaced, they will not be recycled unless it is easy for the end consumer. Think about how many batteries get recycled vs. just thrown in the trash. I advocate for a monthly curbside pick up of misc. items like CFL’s and batteries. We have weekly pickup of co-mingled recycling, except glass. Glass gets picked up once a month. I think some areas can even put their glass in the co-mingled container.

The real interesting thing about the bill you linked to is that it aims to outlaw incandescent bulbs by 2012. I would certainly hope that by then all this is a moot point because of LED lighting technology. But maybe I am too optimistic on those?





6 JD Thomas

Hi Will,

Nope, that theme is freely available on the http://themes.wordpress.net site. I made some small changes to it, but since it supports Widgets I could stick most of my changes in Text Widgets and not have to recreate my sidebars every time I want to try a new theme. My prior theme was by the same folks, but the center column was too narrow and for some reason, there wasn’t an easy way to tweak that in the CSS. Too many absolute positionings.


7 CableGirl

What a great discussion. I feel like I’m always walking through the house turning off the lights my husband leaves on. He says he hates walking into a dark room. Personally, I hate having the house lit up like a Christmas tree.

I have changed the majority of the bulbs in my house over. I love the idea od curbside recycling for things like bulbs and batteries. It is amazing to me how many batteries get disposed of in a single day. (sorry, I can’t remember the site where I read the statistics) The only place I know of to dispose off batteries and the like is the Best Buy near us.


8 Anna

Hi Will, very good point – thanks for pointing out. Few years ago we had a blockout here in Canada, and I still don’t believe that after all this conserve energy warnings, the streets are still uselessly lit up. Anna 🙂 PS Sometimes I get so upset that I have to remind myself not to get stressed too much because it is not good for me, lol. This and politics, no good for me. Anna 🙂


9 Will

Welcome CableGirl – I understand your husband! Walking into a dark room, especially if the light switch is not right at the door, and the room has a coffee table in it, can be murder on the shins! I remember when my kids were little, that a dark rooms, bare feet and their toys, Lego’s, etc. were a bad combination. I use night lights in certain rooms now.

I am going to look into the concept of curbside recycling of odd things like batteries, and fluorescent bulbs to see if the idea is being floated anywhere. The fragility and size of fluorescent tubes may be a problem, but CFL’s wrapped in a newspaper might work. I don’t know though, as the one thing you do not want to do is break one of these bulbs. Another reason we need to get the LED lights on the shelves as soon as possible.

One potential issue with the LED’s after getting the cost down might be resistance from the CFL manufacturers. I am sure they have spent a bundle in recent years getting the production facilities going for them and might not want the market to go to LED’s for many years.



10 Will

Yes Anna, we occasionally have outages, usually only lasting minutes or an hour or two. Most often in the summer when too many people use their AC. Big blackouts, like the one I think you are referring to, are a bigger issue because they can be so widespread. I think our power grid is more vulnerable than most want to admit. CFL’s, LED’s, and anything else that can reduce usage are great, but we also need better technology on an individual building level.

I really thought solar would be more affordable and widespread by now. I remember thinking years ago that by the year 2000 all homes would have solar. It obviously has not happened, unfortunately. I guess the technology has proven harder to adapt than was expected, but solar is getting to be an old technology and should have been more widely implemented by now. I talked to someone who thinks it is a situation similar to that movie “Who Killed the Electric Car?”, but I am not quite that cynical!



11 Will

Hey Techfun, that’s a cool night light! Do you have one? I wonder how their range is? We have a Target right here. I think I’ll see if they have a couple and try them out. Thanks!


12 JD Thomas


You might want to try one of these: Motion Activated Night Light.

I have them in all my hallways and at the top and bottom of the stairs and on the landing and in each bedroom. They are motion activated so when you enter a room, you have enough light to get around and it helps avoid the need to turn on lights if you need to go somewhere in the house at night. Mine are not exactly like that, I suspect mine are brighter since they use a chandelier type bulb.

Maybe that would defuse your husband’s complaints about entering a dark room.


13 JD Thomas

We have a few that are similar to that, but bulb instead of LED. I bet the LED is not as bright.

As far as the solar issue you would think there wold be more of it in use. Although I see some use of it for heating pools in new homes, you don’t see large scale installations.

In the US there is a 30% tax credit, up to a maximum of $2,000, for a solar-powered water heating system that you install for use in your home, provided the system is not used just for heating swimming pools and hot tubs. To be eligible for this credit, the system must be certified by the Solar Rating and Certification Corporation and must produce 50% or more of the hot water needed in the residence. The second credit is for 30% of the cost of a solar photovoltaic (PV) system, also up to a maximum of $2,000.

Those credits are nice, but for a large solar electrical system in to run all the things that we have become accustomed to it can cost upwards of $35,000.


14 Will

I wonder how long it would take to earn back the #35,000??!!

On closer look at that night light, it is an auto sensor, but only to light, not motion. Their description is confusing, but I did find some motion sensitive ones, though, like this incandescent one at Amazon:


15 JD Thomas

That one from Amazon is more like what I have.


16 JD Thomas

Motion Sensing Lights: I think I got mine at Lowes or Home Depot.


17 Catherine

GREAT POST! I was taught as a kid NOT to turn off the lights unless I really wasn’t coming back, because of the saving money bit, so now as an environmentally conscious adult, I’ve never been sure WHAT was best. And now I do!

My husband and I switched over to LED lights at least a year ago and we love them!


18 Catherine

I’m sorry, I misspoke – we use CFL, not LEDs!


19 JD Thomas

We currently use CFLs whenever possible. My partner was looking at LED’s last night and we were looking at the higher price for the product compared with the energy savings over its 10 year life span.

What I wondered and haven’t looked up yet, is whether or not LED’s require any special disposal effort the way CFLs do.


20 Will

JD – I am starting research on a more in-depth article on LED bulbs so I was just looking into their disposal requirements. They do not contain mercury, so are not hazardous, but some, at least do have small circuit boards. I suspect that anything with a circuit board should be recycled, but they are definitely better environmentally than fluorescent.



21 Will

Catherine – LOL! When I read the first post, I got very interested in hearing how the high cost of LED bulbs was overcome by you and you husband. Then I saw your second post!

Do you see an option to edit a post on this site after you publish it? It should be there, but someone asked about it a couple of weeks ago and now I wonder. I always see it, but it might be that you have to be logged in to get the option. If anyone else here can verify that they can edit their posts without being logged in, that would be great. It may also be a cookie thing, but that should not take away the edit option until you clear your browser’s cookies.

By the way, Catherine, I like your reading list!


I get annoyed when I hear that younger people don’t read any more. Even my 13 y.o. reads all the time.


22 JD Thomas

Will: Edit is only there for you since you are the blog owner. It lets you edit out profanity and such.


23 Will

Some of you will probably notice that a few comments disappeared from this article. They were mainly me and JD, (Techfun) discussing a WordPress plugin to edit your comments. Today I published a post dedicated to WordPress plugins. This will enable those of us using WordPress to help each other in finding and implementing tools for our blogs. I moved the comments that were here over to that post:




24 Alan

motion detectors. lights go on when you enter the room and automatically switch off a few minutes after it is vacated. best way to minimize energy waste on un-needed lighting


25 JD Thomas

Alan, they are great. Thats what we were talking about back in comments 10,12,13,14. Do you have a specific model or type you would recommend?


26 Alan

oops. teach me to scroll down to the comment entry screen and not read all the intervening comments. mea culpa. I don’t actually have any recommendations for brands but we use them at work in all rooms that are only intermittently used. when you enter the supply room or the store room or the bathroom the overhead lights come on and awhile after you leave they go off.


27 JD Thomas

Alan: I think we have all done that at least once. I just got my hopes up thinking you might have some residential products in mind specifically. the commercial stuff seems awfully pricey.

I’m considering this for my house:


I already have some X10 devices so it would allow me to save on my outside floodlights and make it easy to find my keys and get in the door coming home late. Having it also turn on a light in the living room would be nice so I don’t trip over my dog.


28 Will

Hi Alan – No oops is necessary. Just glad to have your input. Yes it can get cumbersome when the comment list gets long. On the other hand, I am glad we are having such an educational discussion! Some sites, when the comments get real active and long on a regular basis, add a forum to discuss topics. This has the added advantage of allowing users to start their own discussions, not limiting things only to topics the main author on the site has written about. I don’t think this site is ready for that yet.

I have found motion detector light switches at a local electrical store that sense you when you enter the room and turn on the light. They were about $20.00 each. I did not end up trying one, mainly because we have 4 cats and 2 dogs. I might get one this weekend and install it in a less used room to see how they do.

I would hesitate to use them in large rooms or for switches that control more than one room as once you get out of the detector’s range, the lights might shut off on you. Also, what if you were sitting still reading? Would the light keep going off? I’ll have to investigate.


29 paulette

My opinion regarding this matter is the priority of a person. If one prioritize convenience, ofcourse he wont put the lights off. But for those who are thrifty, i bet they will choose to turn off the lights.


30 Will

Convenience is a big factor for many people. The more a product can be designed to be convenient and practical, in addition to being healthy or green, the more use it will see.



31 Andy

hi there. the majority of the stress on incandescent filaments occurs when the switch comes on, throwing a current thru the cold filament. turning on and off stresses that and definitely reduces the life of the bulb. when you factor in manufacturing and disposal costs, it is better to leave the light on for short periods of time. this is apart from the social/personal preferences people may have. you can put low wattage bulbs around to keep on so your house stays lit, leaving the larger bulbs for brighter light as needed. It’s the surge-of-power issue that is the main reason why the modern bulbs last longer. they use less power. but also, they start slow — dim — and then grow brighter. this reduces the impact of the power surge. most of the wear and tear on the modern bulbs comes from constantly turning them on and off. my wife likes the long-life aspect of these bulbs but is a freak for always turning lights off; then she complains when the new bulbs blow out much quicker than they should! just part of our ongoing marital problems but that’s a different story. some people hate the fact that the new bulbs start dim but they forget the rationale for it. it’s an easy habit to learn to flip the switch, say, in your closet a few moments before you’ll actually have to go in… the energy lost to incandescent bulbs is enormous.


32 Coach G.

Why does everyone use this silly idea that the time the lights are on is all that matters? It actually does take a lot of power to get the lights turned on and then much less to keep them going. Why is this ignored by everyone? It is simple physics. If that were not true then there also would not be a surge to worry about wear and tear on the bulb. How can you talk about one, but ignore the other?

I guess common sense just isn’t so common any more.


33 Will

Hi Coach! Thanks for bringing up that. That had not occurred to me and when I thought about it, still did not make sense. So I did a quick Google search and found several sites that say it is a myth that it takes more power to turn on a light than it does to keep it running. Below is a quote from the Mr Electricity site that covers a few other incorrect assumptions as well. I’ll look again tomorrow and if I find anything that supports the idea of extra power consumption negating turning off a light, I’ll post it here.

From Mr Electricity:

I’m amazed at all the bizarre misconceptions people come up with. It seems like there’s no end to it. Examples include:

* The idea that it takes more energy to turn on lights or computers than to keep them running.
* The idea that it takes more energy to turn on the AC when you get home from work rather than to run it all day.
* The idea that a lamp uses energy even when it’s turned off.
* The idea that a 60-watt bulb uses more energy than a 100-watt bulb.
* And now this: Someone who thinks that one light bulb uses the same amount of energy as two light bulbs.


34 Mike Touch

Got brought up where you were shouted at if you left the lights on.

This is also a Summer thing. In the Winter lights can be left on as the wasted energy is used to heat your home thus decreasing the time the heating needs to be left on!



35 Betty

Talking about turning off light for saving, the government of my country has made policy to increase the electricity cost. Starting from this month the cost will be 245% increase…So, for me now turning off lights is more economic sense.


36 Will

245%! That’s scary. But when I think about it the cost of natural gas here has gone up that much over the past 5 or 6 years. What country are you in?


37 troy

This was a great mythbusters show. I enjoyed it alot and reading your post help to confirm what my mom and dad used to hound me about for years when I was a kid, turn out the lights when you leave a room.

who would have guessed years later something simple like this can not only reduce costs, but help the enviroment, thanks

troys last blog post..Facts on Global Warming, Is Global Warming Real?


38 Will

Yes, turn them off. LOL! I also heard that a few times when I was a kid. The new technologies that automatically dim or turn off lights when a sensor detects an empty room are neat. I guess they used to turn off lights when people were sitting in a chair reading, but now they use a better detection method that supposedly does not do that. There are also little switches on the new ones to override the sensor if for some reason you want lights left on in an empty room. The key to this technology being widely accepted is making it reasonable and controllable. If you can override the settings when you need to, most people won’t object to them.


39 komodo dragon

def. turn the lights off! I have always been told this as a kid, and it is really important. I love the fact that mythbusters did an episode on this debate 🙂


40 Will

KD – Wow! Those are some mighty lizards! Thanks for the comment!


41 Easy Ways to Go Green

I also have questions about the efficiency / productivity of the little devices they sell that serve as a power reducer, and plug into the wall outlets. You are supposed to plug devices into these adapters, which then cut the power being channeled into things (even when they are not in use). Any word on these? Even an opinion?


42 Will

I’ll have to look at those. I had not heard of them, although years ago a little button thing was made to reduce power to light bulbs. It made them a bit dimmer, but increased their life span. I would think reducing the power to chargers and such would hinder how they work.


43 Kevin (Sauna-Talk.com)

To answer question 41 – these “power reducers” as you call them are a combination transformer/rectifier. It reduces the AC current down to say 9V and then the rectifier (a diode/capacitor combination) turns the AC current into DC. All transformers have leakage current, so anytime the primary is energized it will draw a little power.


44 Will

Thanks for that explanation, Kevin!


45 Greg

This was a fascinating article, you always hear people say that the lightbulb burns more energy turning on and off so people reason that’s it better to leave it alone, but your article really helped to educate me that you are far better off turning that light off even if your leaving the room for a miniute or two, I guess every miliwatt saved is better for the enviroment, thanks


46 Steve

Hi Will, I was checking in and saw this post on the “recent comments” link. It’s a great write up, and as usually, you cover both sides. I remember in school (way back) the rule of thumb was don’t turn the classroom lights out (long fluorescent type) if it was for 15 minutes or less because of the extra power used when they were turned on. I don’t know if there’s anything to that (I doubt it). I also remember my dad always telling us to TURN OFF THAT LIGHT, which is what I do with my kids now. I changed to CFLs about three years ago throughout the house, and it cut our electric bill at least in half (we were in the second tier which costs more per KW but that’s another story). I love the CFLs, except the ones in the bathroom last less than a year! If you turn them on and off all the time, you don’t get anywhere near 10,000 hours! I’m convinced they have a limited number of power ons, so as you point out, you’ve got to look at the cost of the bulb and the power and resources used to produce it. You may save a few pennies on electricity, but need to buy a new CFL bulb much sooner. It really depends on how long you’re turning it off for (only 4 or 5 minutes?) Seems the devil is always in the details. Maybe I’ll work up the cost numbers. Wow, brain dump…
~ Steve (aka “trade show booths”)
PS. I can’t wait for the LED bulbs to become more affordable.


47 batteries

I like the way you explain the it. I want to take it to a larger spectrum by not just thinking about bulbs and the cost of it. It is not just money.By turn out light we are not saving just energy we are saving our environment too,isn’t it true? Think about it and reply on it.


48 Coach G

I notice that no one ever mentions the extra challenge to the environment when disposing of compact florescent bulbs.

Also, I still don’t get how you can have it both ways with the power surge at the point of turning on a bulb. Either there is a power surge, or there isn’t. If there is a power surge, then it costs extra. If there isn’t a power surge then everyone who thinks that turning bulbs on and off more often wears them out faster, is just off their rocker.

It doesn’t work to say there is a power surge that wears out the bulb faster, but the surge takes no extra electricity. A surge by definition is extra electricity.

Somebody is living in a dream world.
.-= Coach G´s last blog ..Whole Grain Foods : Corn ??? =-.


49 Will

Hey Coach G – Thanks for the comment. Did you see that you also commented on this post, (#32), above? I don’t know about the surge, but I do know that bulbs seem to burn out only when they are just turned on. I have never seen one go while it was glowing.

Also there are several posts on this site, some with quite long comment threads, that discuss the environmental problems of disposing of cfl’s. It is a big problem that as you say is ignored by many. Not me though! 😉

Anyway thanks again, it is late and time for me to go off to my real “dream world”.


50 Tony McGurk

My Dad was always big on telling us kids to turn the lights off when we left a room so I have grown up with the habit. I’ve never really considered the possibility of shortening the life span of the bulb before. I just always flick the switch off. Sometimes I have turned a light off leaving my wife in the dark as I have walked out of a room. Just habit


51 Tony

My Dad was always big on telling us kids to turn the lights off when we left a room so I have grown up with the habit. I’ve never really considered the possibility of shortening the life span of the bulb before. I just always flick the switch off. Sometimes I have turned a light off leaving my wife in the dark as I have walked out of a room. Just habit


52 Home Lighting

I always use to turn off the lights of my home whenever I go outside. I am agree with you Mr. Will. You had well explained each and everything in your post regarding effect on economic and environmental.


53 Christmas Lights

Just love that Tony! I too grew up turning lights off, though my habits have altered and not for the better. For me personally it is not about the light bulbs it is that increased reliance on the energy and the world is ablaze with the light. This is not a natural occurrence and somewhere I believe we will see the damage to our plant life, nature and of course we humans will continue to increase out reliance and science will find solutions to making the globes last longer.


54 Chris

I bought a pair of 40 watt LED lights for a gooseneck lamp and I am very dissapointed that one of them has already blown out. These things are supposed to last ten years and one has barely lasted more than a week. I never had this problem with any other light.

They seriously need to get to basics down before they go mainstream, because a lot of people are going to be dissapointed when they pay $20 for a light bulb that goes bad in a week.


55 Will

Hi Chris – One of the justifications for the high price of LED light bulbs is that they last “20 times longer” than incandescent. Your experience is disappointing. Price needs to come WAY down to make them worth it. It won’t be too long, (2012 -2014), before the law preventing sales of incandescent bulbs goes into effect so I hope these problems get worked out before then.


56 Keith

I am constantly changing light bulbs to CFL. I just pray that in 10 years or whenever they burn out, that the technology has advanced far enough that the mercury will be able to be recycled out of them.


57 Will

You know Keith, I have changed lots of our bulbs to CFL’s over the past few years. I have noticed that they do not always last as advertised. I have several that are still going strong after 2 or 3 years, but I have had a few burn out after only a few months.


58 Peter

Nice article- I think that you should also mention that you can save money by switching to CFL light bulbs or LED light bulbs


59 Anonymous

As an electrician in Springfield MO, I would say that turning the lights off if you’re going out for more than 5 minutes is a good idea. But if you really want to save from electricity costs, use LED lights. Their prices might be higher than our usual bulbs… but they’re worth it! Plus, their life span is way longer.:)


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