Efficiency of incandescent light bulbs as heaters

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?

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.

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.

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. :slight_smile:

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

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

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.

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.

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?

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.

No, touch a flourescent and an incandescent bulb.

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.

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.

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

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.

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.

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.

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%.

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.

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.

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.

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.