# Efficiency of incandescent light bulbs as heaters **URL:** \ **Category:** Factual Questions\ **Created:** [February 11, 2003, 1:59am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259 "2003-02-11T01:59:58Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 12, 2003, 2:11am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/21 "2003-02-12T02:11:35Z")
And all this assumes you are using resistance electric heating, NOT a electric heat pump, NOT gas, NOT oil (or other non-resistance heating). ALso changing your lightbulbs seasonally is a good way to break them by dropping them, twisting the glass out of the metal and just banging them around. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 12, 2003, 2:12am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/22 "2003-02-12T02:12:48Z")
I’m not so sure if the electric heat is 100% efficient. It’s been a while since I studied thermodynamics, but using a heat pump (air conditioner) as a heater gives you efficiency higher than 100%, doesn’t it? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 12, 2003, 2:16am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/23 "2003-02-12T02:16:34Z")
No. There’s no such thing as greater than 100% efficiency. You can’t get more power out of a device than you put in. In any real system, there are always losses so that, in fact, you always get less power out than you put in. Electic heat is no exception. In fact, electric heat is less efficient overall than gas heat. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [February 12, 2003, 2:17am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/24 "2003-02-12T02:17:04Z")
Electric heat is 100% save for the loss in wiring from the source to the load. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 12, 2003, 2:23am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/25 "2003-02-12T02:23:30Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > **No. There’s no such thing as greater than 100% efficiency.** By “efficiency” I meant the ratio of heat input to consumed electrical power. Air conditioners are heat pumps, not isolated devices. Are you saying that a heat pump using 100W of power can never transfer heat at a rate greater than 100 W? ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 12, 2003, 2:26am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/26 "2003-02-12T02:26:09Z")
> [@](#): > > but using a heat pump (air conditioner) as a heater gives you efficiency higher than 100%, doesn’t it? Yes - in a way. A heat pump uses energy to transfer heat from one place (outside) to another (inside). It works out that you can transfer more heat then the energy you use to do it. Also as a side benefit most of the energy you use is also converted into heat. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 12, 2003, 2:40am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/27 "2003-02-12T02:40:43Z")
> [@](#): > > Resistance heaters use metal elements that have a high resistance to the passage of electricity. When forced to conduct electricity, they heat up. Because almost all of the electricity passing through the element is converted to heat, resistance heaters are considered almost 100 percent efficient. However, if the losses associated with the generation and transmission of the electricity to the site are included, the efficiency drops. Because electricity is considered such a highly refined form of energy essential for many tasks in our modern society, some consider it wasteful to use it simply for heating. In addition, on a BTU for BTU basis, resistance is one of the most expensive ways to heat. From [this site.](http://tva.apogee.net/res/reheovr.asp) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 12, 2003, 2:48am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/28 "2003-02-12T02:48:18Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\*Are you saying that a heat pump using 100W of power can never transfer heat at a rate greater than 100 W? \*\* No, I’m only saying that the power put into a unit cannot exceed the power extracted from it. Otherwise you’re into the realm of perpetual motion. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 12, 2003, 2:59am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/29 "2003-02-12T02:59:19Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*From [this site.](http://tva.apogee.net/res/reheovr.asp) \*\* It goes on to say: > [@](#): > > Heat pumps use electricity too, but instead of using it to create heat, they use it to move heat from one place to another. Because it is moving rather than creating heat, they can achieve efficiencies of over 300 percent, meaning they provide three times more heat than they consume in electricity. Central air conditoners are heat pumps. The OP did not specify which type of electric heat he has, but if it’s an air conditioner then it’s more than 100% efficient. Therefore it’s better to use fluorescent lights and let the air conditioner do the heating. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 12, 2003, 3:31am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/30 "2003-02-12T03:31:09Z")
**scr4** is correct. ---
**Author:** ![prisoner6655321](https://avatars.discourse-cdn.com/v4/letter/p/5f8ce5/32.png) [@prisoner6655321](https://boards.straightdope.com/u/prisoner6655321)\ **Post date:** [February 12, 2003, 4:52am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/31 "2003-02-12T04:52:16Z")
They say that artificial lighting is energy you pay for twice, once to provide the light, and again to remove the heat generated by the light. Remember what light is: energy. All light is converted to heat. None of this 25% business. This is VERY serious in Architecture (my field.) Did you know that large buildings generally have no need for heaters? (Except at night.) They can be in cooling mode even in the coldest day. Large buildings are what you call “internally load dominated.” Which means that the heat generated from the energy used inside the building is in excess of the normal comfortable temperature. Most of this heat is provided by… tada… artificial lighting. However a house is “externally load dominated.” It is succeptible to outside temperatures and the sun. Internal lighting is relatively negligable, but it can make a small impact. Your inclination might be to say, “go for the incandescent.” But then think a bit. There are many more efficient sources of heat than an incandescent bulb. Your electric furnace is more efficient than the electric bulb. So that should answer your question. Consider the /BTU for your furnace and the /BTU for your light bulb. Sorry, I probably could have figured out the result in school, but that was a few years past. I can say from intuition and experience that CFL + more furnace is better on your pocketbook than incandescent + a little bit less furnace. Now if you want to talk about quality of light, then that’s another matter altogether. I prefer halogen myself. MUCH brighter and MUCH more heat (and Danger of fire.) But the quality of light is better with halogen. Incandescent is 2nd, and fluorescent is, well, it’s pretty much last if you don’t count metal halide or sodium fluoride (those annoying parking lot lamps) which you don’t use inside anyway. Not in a house anyway. Since fluorescent lamps output fewer lumens, they will be a bit cooler. And it takes less energy to light them. So short answer, taken from this Architect who has studied Sustainable Design. Go with the compact fluorescent, if you are comfortable with the (lack of) quality of light. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 12, 2003, 5:24am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/32 "2003-02-12T05:24:44Z")
This thread is getting really annoying. > [@](#): > > \*Originally posted by prisoner6655321 \* > **Most of this heat is provided by… tada… artificial lighting.** You’re going to have to provide a cite for this. I’d be surprised if energy consuption for lighting exceeded that for computers and other bits of office equipment. > [@](#): > > \*Originally posted by prisoner6655321 \* > \*\*There are many more efficient sources of heat than an incandescent bulb. Your electric furnace is more efficient than the electric bulb. So that should answer your question. Consider the /BTU for your furnace and the /BTU for your light bulb. \*\* Unless the “electric furnace” is a heat pump, as discussed by **scr4** , the electric bulb is likely to be _more_ efficient than the central heating, because it doesn’t incur any losses in the duct work. > [@](#): > > \*Originally posted by prisoner6655321 \* > **Since fluorescent lamps output fewer lumens, they will be a bit cooler.** “Lumens” refers to light, not heat. What are you talking about? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 12, 2003, 5:30am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/33 "2003-02-12T05:30:47Z")
> [@](#): > > \*Originally posted by Desmostylus \* > **This thread is getting really annoying.** No one’s making you keep checking it. 😛 ---
**Author:** ![prisoner6655321](https://avatars.discourse-cdn.com/v4/letter/p/5f8ce5/32.png) [@prisoner6655321](https://boards.straightdope.com/u/prisoner6655321)\ **Post date:** [February 12, 2003, 5:35am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/34 "2003-02-12T05:35:57Z")
> [@](#): > > _Originally posted by Desmostylus_ > “Lumens” refers to light, not heat. What are you talking about? It’s already been said (correctly), that once light is absorbed it is released as heat. Light is energy. The energy has to go somewhere. I’ll work on the light fixture as heat cite. ---
**Author:** ![BrandonR](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@BrandonR](https://boards.straightdope.com/u/BrandonR)\ **Post date:** [February 12, 2003, 5:37am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/35 "2003-02-12T05:37:59Z")
Hey it’s the straight dope… Where there’s rarely a straight answer. 😉 ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 12, 2003, 5:44am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/36 "2003-02-12T05:44:38Z")
> [@](#): > > \*Originally posted by prisoner6655321 \* > **It’s already been said (correctly), that once light is absorbed it is released as heat. Light is energy. The energy has to go somewhere.** I know that’s it’s already been said. I said it. But if the fluoro is providing fewer lumens, the room is going to be _darker_, which means that you haven’t sized the fluoro properly. ---
**Author:** ![prisoner6655321](https://avatars.discourse-cdn.com/v4/letter/p/5f8ce5/32.png) [@prisoner6655321](https://boards.straightdope.com/u/prisoner6655321)\ **Post date:** [February 12, 2003, 6:01am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/37 "2003-02-12T06:01:42Z")
> [@](#): > > _Originally posted by Desmostylus_ > But if the fluoro is providing fewer lumens, the room is going to be darker, which means that you haven’t sized the fluoro properly. You are correct sir. Still, it does take less energy to provide the same amount of light. Think about this… > [@](#): > > The standard A lamp incandescent bulb is the cheapest lamp to buy and the most expensive to operate. An incandescent bulb uses **ten percent** of electrical energy to create light, while the other ninety percent creates heat. > _Source: The Ecology of Architecture By Laura C. Zeiher. 1996. Pg 112._ So I have to admit the 25% thingy is actually too conservative, despite my little comment before. Doesn’t invalidate my argument though. > [@](#): > > _Originally posted by Desmostylus_ > You’re going to have to provide a cite for this. I’d be surprised if energy consuption for lighting exceeded that for computers and other bits of office equipment. Okay, I just found one thing in one of my books. Sorry, no website. You’ll just have to trust me or check it yourself in the library. Earlier in the book I quoted above, first sentence on page 112, Laura states that “The illumination of buildings is responsible for 20% of electricity consumption in the United States.” Now I realize that that’s not over 50%, but this isn’t the electricity consumption of an average large building. It is 20% of ALL electrical usage in America. Still, no real number. We would have to guess. Let me see if I can find some better sources. I’m sure I have that somewhere… now where are my text books. CRASH. Mumble mumble. ---
**Author:** ![something\_clever](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@something\_clever](https://boards.straightdope.com/u/something_clever)\ **Post date:** [February 12, 2003, 6:03am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/38 "2003-02-12T06:03:58Z")
point is… dude. despite all these technical arguements… 1. replace every bulb in the house with CFL 2. buy a freaking PROPANE or similar gas heater, its like 7 cents an hour or less to heat a huge ass area. by the way, yes, bulbs do make a difference in heat… i used to work in the mall at structure and of course you guys know every store has a thousand lightbulbs… up front where the jeans were, there were those huge 100w floodlights… all of the jeans were always warm if they were in the path of a floodlight, the ones not in the path were much cooler. the front of the store had way more lights than the middle, and you could defnitely tell the temperature dropped once you got away from all the floodlights. ---
**Author:** ![prisoner6655321](https://avatars.discourse-cdn.com/v4/letter/p/5f8ce5/32.png) [@prisoner6655321](https://boards.straightdope.com/u/prisoner6655321)\ **Post date:** [February 12, 2003, 6:19am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/39 "2003-02-12T06:19:34Z")
> [@](#): > > _Originally posted by Desmostylus_ > You’re going to have to provide a cite for this. I’d be surprised if energy consuption for lighting exceeded that for computers and other bits of office equipment. HAH! I found a source, on the web no less…[http://scom.hud.ac.uk/scomjm4/maport/brimod/Page9.htm](http://scom.hud.ac.uk/scomjm4/maport/brimod/Page9.htm) > [@](#): > > Artificial lighting is a substantial consumer of energy in offices and can account for 50 per cent of electrical consumption. Sorry if I annoyed you Desmostylus. Can I go to bed now? ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 12, 2003, 6:33am UTC](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259/40 "2003-02-12T06:33:02Z")
You can go to bed. I’m not trusting data from a page that says “polimer” and “total internal inflection”, so I’ll try a find a proper cite. [Previous page](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259.md?page=1) [Next page](https://boards.straightdope.com/t/efficiency-of-incandescent-light-bulbs-as-heaters/154259.md?page=3)