Efficiency of incandescent light bulbs as heaters

[Yeah]

If my house has electric heat, and the ratio of the price of a compact fluorescent bulb to an incandescent bulb is equal to the ratio of the lifetime of the fluorescent bulb to the incandescent bulb, then should I use incandescent or compact fluorescents bulbs for light in winter? Or does it matter?

[Q.E.D.]

If you're looking to save money on your electric bill, fluorescent is the way to go, hands down. The amount of heating you'd get from a typical 100W light bulb is practically negligible.

[antechinus]

If you live in a cold climate, where the house is thermostatically heated, then the heat from the incandescent will offset heat introduced by the room heater.

Also depends on placement of the bulb. The bulb could be heating up a ceiling, leading to heat loss from the house, rather than it warming the house.

So use an incandescent, unless you use energy to cool the house.

[carnivorousplant]

Heating is what incandescent does best. More radiation in the IR than the visible. However, you'd need 15 100 W bulbs to equal a 1500 Watt electric heater and they'd keep you awake at night.

[Q.E.D.]

Originally posted by carnivorousplant
Heating is what incandescent does best. More radiation in the IR than the visible. However, you'd need 15 100 W bulbs to equal a 1500 Watt electric heater and they'd keep you awake at night.

Not quite. 25% of the energy thst goes into a bulb is turned into light. The other 75% is given off as heat

[carnivorousplant]

You are right of course. 1500/.75 would mean 20 100W bulbs.
Thanks.

[The Flying Dutchman]

Originally posted by antechinus

Also depends on placement of the bulb. The bulb could be heating up a ceiling, leading to heat loss from the house, rather than it warming the house.

I disagree. Incandescent bulbs heat radiantly, affecting the solid objects in the room. It doesn't matter whether the source is close to the ceiling or the floor. Convection wiill of course concentrate warmer air near the ceiling either way. I know this because I once research options for ceiling and under floor radiant heating systems for a house I once built. I chose the ceiling system, and it resulted in the cheapest and most comfortable and silent heating I have ever experienced.

[Desmostylus]

Originally posted by Q.E.D.
Not quite. 25% of the energy thst goes into a bulb is turned into light. The other 75% is given off as heat

No, that just isn't right. Apart from any light that escapes through the windows, the light ends up as heat, too, when it gets absorbed by surfaces in the room.

[Achernar]

Isn't this going to be true of any electrical appliance? All the power it consumes will wind up as heat, one way or another?

[Q.E.D.]

Originally posted by Desmostylus
No, that just isn't right. Apart from any light that escapes through the windows, the light ends up as heat, too, when it gets absorbed by surfaces in the room.

Close, but no cigar. Some of the light may be reradiated as heat, but not all. Some is stored as chemical enrgy in molecular bonds and some is reradiated as fluorescence.

[carnivorousplant]

Originally posted by Achernar
All the power it consumes will wind up as heat, one way or another?

No, touch a flourescent and an incandescent bulb.

[Desmostylus]

Originally posted by Achernar
Isn't this going to be true of any electrical appliance? All the power it consumes will wind up as heat, one way or another?

Yes, pretty much. But it won't necessarily end up inside the room. In an air-conditioner, the heat ends up outside the room. Same with the light from, say, a lighthouse.

Originally posted by Q.E.D.
Close, but no cigar. Some of the light may be reradiated as heat, but not all. Some is stored as chemical enrgy in molecular bonds and some is reradiated as fluorescence.

This is getting silly. Any re-radiation by fluorescence just means that it takes a bit longer for the light to finally turn into heat. As for the rest, how much photochemistry really takes place? It takes decades just to fade the carpet.

[Yeah]

Thanks, all, for your interesting comments. Now, how about an answer to the original question?

[Desmostylus]

Okay. If the electric heating system that you use is thermostatically controlled, then the heat output from the lights, whatever kind they are, will reduce the load on the electric heater.

If you take out the CFLs during winter and replace them with incandescants, you'll prolong the life of the CFLs, and not increase your power bill.

[Desmostylus]

On re-reading, you've stated the the capital cost per hour of use is the same for the incandescant and the CFL. So in that case it makes no difference.

[Uncommon Sense]

Originally posted by Q.E.D.
If you're looking to save money on your electric bill, fluorescent is the way to go, hands down. The amount of heating you'd get from a typical 100W light bulb is practically negligible.

The first reponse was the correct one.

Desmostylus - You`re over engineering the answer. Simply, the incandescents will not make a difference in your average home. If you were burning four 100w. bulbs in a bedroom, you will notice the heat. For practical purposes the lighting in a home never plays a role in the heating calculations. It is a waste of money to alter your lightning to try to get heat gains out of them.

Go with the flourescents to save money on your electric bill.

[bbeaty]

25% of the energy thst goes into a bulb is turned into light. The other 75% is given off as heat

Huh? 25? Incandescent bulbs are more like 5% efficient. 95% output as infrared and convective heat. It's the Compact Fluorescent ones which are around 25%.

Some of the light may be reradiated as heat, but not all. Some is stored as chemical enrgy in molecular bonds and some is reradiated as fluorescence

Chemical energy?!! Don't let physics theory interfere with practical considerations. You're essentially talking about incandescent light bulbs being inefficient heaters because their ultraviolet light is being lost in chemical reactions. In reality this loss is far too small to be significant. Loss to fluorescence might be an issue, but it's also insignificant because the re-radiated light still heats the room.

As for the OP question, is he going to remove all the incandescent bulbs at the end of winter?

His electric bill will remain the same whether 100W comes from the heaters or the bulbs, so there's little difference between fluorescent and incandescent bulbs. However, it's very inconvenient to "turn off the incandescent heaters" by having to replace or install bulbs depending on the season. And if you don't, then the 95% inefficiency of incandescent bulbs will become an issue in the summer.

[dtilque]

I agree with Desmostylus and bbeaty. It makes no difference to your power bill. And changing all your light bulbs twice a year will be a pain in the butt.

A 100 W incandescent bulb will offset 100 watts of heating that your electric heat will have to produce. An equivalent fluorescent light will only consume 25 W or so, but those 25 watts will also offset 25 watts of electric heat. You get about the same amount of light and the same amount of heat from the same amount of electricity either way. Any losses from light going out the window will be the same either way.

The power savings with fluorescents only come when heating is not desired or if you have non-electric heat.

[antechinus]

Good grief, what has been happening to this thread?

It is simple. If you have a cold-climate house, the waste heat from the lightbulb offsets the general room heating - so use an incandescent (unless you have some weird thing for fluoros). The energy use is the same.

If you live in a warm-climate house that aircon cools, then it is obvoiusly cheaper to use a fluoro.

If the house has both heating and cooling - well I am sure you can work out how to install two different light sources in a room.

grienspace - Heat loss through the ceiling would be mainly by conduction and convection. Light bulbs are put on ceilings. OK, you could put the bulb on the wall and the same would happen - just less convection. The point is an incandescent bulb heater placed near a point where heat can leak from the system, via conduction (mainly) and convection, would be a loss that would not fully offset the general room heating. Radiant heat is negligible.

QED - What's that crap about fluorescence. I wont even bother.

I thought my first post explained things.

Of course, Desmostylus and bbeaty are both correct.

[Yeah]

Thanks. I conclude from the responses that it doesn't really matter for most bulb placements but that fluorescents would be a wee bit more efficient for light fixtures "placed near a point where heat can leak from the system" such as a ceiling-mounted light fixture below an unheated attic.

[kanicbird]

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.

[scr4]

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?

[Q.E.D.]

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.

[carnivorousplant]

Electric heat is 100% save for the loss in wiring from the source to the load.

[scr4]

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?

[kanicbird]

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.

[Q.E.D.]

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.

[Q.E.D.]

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.

[scr4]

Originally posted by Q.E.D.
From this site.

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.

[Desmostylus]

scr4 is correct.

[prisoner6655321]

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.

[Desmostylus]

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?

[Q.E.D.]

Originally posted by Desmostylus
This thread is getting really annoying.

No one's making you keep checking it.

[prisoner6655321]

[i]Originally posted by Desmostylus[i]
"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.

[BrandonR]

Hey it's the straight dope... Where there's rarely a straight answer.

[Desmostylus]

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.

[prisoner6655321]

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.

[something clever]

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.

[prisoner6655321]

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

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?

[Desmostylus]

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.

[Cheesesteak]

After reading all these arguments, I'd say that heat wise, the two types are identical. Any savings from fluorescent are pretty much offset by add'l heating cost. However, in the summer, the fluorescents will be a boon, reducing both your lighting costs and cooling costs. Rather than deal with 2 sets of bulbs, go for the fluorescent.

[Uncommon Sense]

Get some cats for the winter months. (click on the HEAT TRANSFER link to the left)

[Uncommon Sense]

here
here
here
especially here
if your concerned about your chickens
and finally here

If you would be so kind as to allow me to retract my earlier post regarding this issue. I`ll will say that the incandescents will add heat to the house. In the summer too.
A point to add to the discussion is that the thermostat is either mounted on the baseboard (electric) heater or on the wall nearby.
The heat rising from the baseboard heater will have way more effect on the thermostat than any incandescent lighting will. Since much of the heat from the bulbs will stay near the ceiling.