I realize that incandescant bulbs create more heat than light, but...

I’ve been pondering this for awhile now. It seems to me that even though incandescant light bulbs make more heat than light, they wouldn’t be that much less efficient than flourescent during the winter months. Why, you ask? Because any heat that bulbs produce would heat the room up, thereby decreasing the time the room heater is on.

I suppose it would depend on what kind of heating system you have. But, if you’re room heater ran off of electricity, are bulbs really that much more inefficient than tubes if you take that into consideration?

Or, am I completely insane? Any help would be greatly appreciated.

You’re right on the money. Provided that none of the light shines out the window, a 100 watt bulb will heat up a room exactly as much as a 100 watt electric space heater. Now whether electricity is the most efficient way to heat your house is a different issue…

I have seen light bulbs that are designed to thrown out lots of heat but they put a lot of stress on the lighting circuit wiring which is usualyy is installed with just illumunation capacity in mind rather than heating which generally takes a lot of current.

I have seen manufacturers and designers of heating managements systems, inslation makers, and energy efficiency assessers use computor models that are designed to simulate human activity and its effects on energy use in an average household.

Part of that model takes into account the lighting as a heat producer and also the heat given off by the human body.

So in answer to your Q then yes incandescant lighting does have an overall effect on the temperatiure inside a building but since the object of a light bulb is to produce light flourescants are far more efficient.
Most folk woud find it inconvenient to change their light fittings every summer and winter just to gain the relatively small benefit of a heating effect when they would almost certainly need other sources of heat anyway.

Well, a 100 watt heater ain’t much. All those little bathroom heaters are 1500 watts to begin with.

Also, a light bulb is usually way up near the ceiling, and since heat rises, all its heat output is already home, and doesn’t see any reason to go visiting down at floor level.

And I’m not a thermal engineer, but I’d think that any heat the light bulb put out would be rather quickly dissipated in an average size room, say 12 by 14 by 8, so unless the room was perfectly insulated, the light bulb wouldn’t have much effect on how long you had to run the heater.

As others have pointed out, a 100 watt bulb does provide 100 watts of heat to the room. As Duck Duck Goose pointed out, if the bulb is on the ceiling, some of that heat is wasted (although ultimately the heat goes somewhere, it may not be where anyone can feel it- for example, the space between the two floors).

A lamp can make more of a difference. Even though 100 watts isn’t a lot of heat, it is some, and reduces the heating load on whatever is heating the house. If you’re willing to discount 100 watts of heat as insignificant, then you shouldn’t worry about wasting energy with 100 watt incandencents vs. fluorescents :slight_smile:
I can feel the heat from my reading lamp, and it does make a difference (of course it’s a 500 watt halogen ;)).

Of course, 100 extra watts of heat isn’t going to help much in the summer, if your air conditioner is trying to cool the house. Also, as someone else pointed out, electric heat can be expensive, so if you’re using oil heat, for example, you may be losing money by letting the lights absorb some of the heating load.


You’re correct, in the winter light bulbs and other appliances are basically “free” if you have electric heat. The down side is that during the summer if you use air conditioning you have to remove that heat, so a 100 watt bulb consumes 200+ watts.

Not only light-bulbs give off heat, of course. I’m not sure what the heat output of the average CRT computer monitor is, but I do know that my big monitor puts out a lot of heat, and when I have both computers, their monitors, and the mixer and sound system on, I don’t have to put the electric heater on in my room. :slight_smile: It hasn’t been on in years, even in winter…

And it’s not just light bulbs… most things you plug into a wall outlet (or anything hardwired into your home’s electrical system) is a “heater,” i.e. close to 100% of its electrical energy is turned into heat. This includes your television set, computer, etc. Notable exceptions include some things with motors.

One other complication with light bulb saving you money on your heating bill: if you’re light bulb is far from the thermostat (like on the other side of your house), the bulb won’t have much of an effect on the heater, since no heat will get back to the thermostat. The heater will run just like it would with no bulb, but you’ll be a little warmer in the lighted room (whether you wanted to be or not). No money is “saved” here, unless you walk over to the thermostat and set it back a tiny amount to compensate. The air conditioner in the summer won’t have a increased load, either, if the thermostat isn’t affected by the bulb- again, you’ll just be a little warmer in that room, unless you move the thermostat back.

I’ve got a room that gets quite warm with my 500 watt halogen, computer, monitor, TV, printer, and 6 to 8 wall adapters for various gadgets :slight_smile: Not to mention me- I think a person at reset is the equivalent of 200-300 watts.


Yeah, but once they’ve been powered on for a while, their dissipation goes down somewhat. :slight_smile:

Actually, average power dissipation of humans is usually a bit less, around 150W.
A naked person not breathing and levitating in a 25 C room would radiate about 60W. With profuse sweating in a hot environment, humans can dump up to 2000 watts, though.

In addition to everything said so far, if fluorescents can ever be bought cheaply enough, their longer lifetime would outweigh the heating savings of incandescents.

Human power is the wave of the future! Don’t you remember the matrix?

Anywas, I’m the reason for the power crisis, heh. I’ve got an electric water heater, electric stove, and electric heat.

There is a oil furnace in the basement, but, it has the unfortunate property of getting the upstairs hotter than the downstairs. I guess the furnace could be on and turned down a few degrees, with an electric heater downstairs.

Anyways, I think the nozzle would have to be cleaned before the furnace could be used. It has been off for 6 years or so. Not to mention the incredibly high prices of oil compared to a few years ago.