Peter vs. Paul– Politics of the Nags

When it comes to turning off lights around the house, my wife is a nag (not as a member of the National Association of Gals, but one who incessantly nitpicks on her own).  “You’re wasting electricity” she will say, approximately thirty eight thousand times per day (give or take).  Similarly, the political nags (not NAGs) are ordering us to use CF lights instead of the tungsten filament jobs, saying we’re destroying the very planet with our light bulbs.


If we cast aside all arguments about rights and liberty (and if we have a chance to toy with other people as a means of boosting our self esteem, why wouldn’t we?) there is the issue of home heating during the cooler months.  I gathered my family together, and explained this to them in terms anyone can understand;


If you have a 100 Watt light going full time inside a heated living space, that’s 100 fewer Watts, on average, that the home heating system has to put out. You have shifted 100 Watts of your energy use from the heater to the light bulb.  Your total usage is exactly the same.  Same goes if you leave the refrigerator open a little longer, or the television on all night.  If you’re heating that space anyway, it makes no significant difference.


Say I have a 10 KW electric furnace.  I could hook up 100 light bulbs, each rated at 100 Watts, through a relay to my thermostat (assuming I had the proper wiring) thereby taking all the heating load off the furnace and placing it on the light bulbs.  Will my heating bill change?  Maybe, and maybe not.  It would depend on the distribution of the lights within the house, the quality of the insulation on my furnace duct work in the cold space under the house, and a few other minor variables.  Maybe I’d save a few pennies, and maybe I’d loose a few pennies.  If you have a gas furnace the situation is still the same– you’re just trading back and forth between gas and electricity, but your total energy usage is going to be about the same.


The situation is completely different in the summer of course.  The waste heat from your TV, fridge, etc., is of no use to you.  If you’re running an air conditioner, anything else in your house that produces heat is causing the AC to work harder.


In both cases, insulation, windows, door seals, and the structure’s orientation and exposure to the sun will overwhelm the other issues.


So we can stop nitpicking each other.

9 thoughts on “Peter vs. Paul– Politics of the Nags

  1. AND CFs are toxic. Talk about contradictory legislation. “You can’t have lead in this but you must have mercury in that?” WTF?

  2. I would imagine that the heating efficiency of your 100W light bulb is significantly lower than 100 Watts worth of your electric heater, especially since the bulb is supposed to be giving off light, not heat. Yeah, I know, incandescent bulbs aren’t all that efficient as far as the amount of light they give off for a given input of electricity. That’s one of the ways that the CF bulbs do so well is that they use a different mechanism for generating light (they aren’t heating a piece of metal to the point of glowing) that is a lot more efficient.

    And, you’re right that other factors (such as insulation) are a bigger factor than almost everything else anyway.

    But, light bulbs are going to give off a whole lot less heat for the same amount of juice flowing through them than your furnace is.

    I’m just sayin’

  3. TheGunGeek, except for the light that escapes the building the light produced by the bulb ultimately ends up as heat.

    Details are as follows: With each interaction with objects within the building the light is either reflected, absorbed, or transmitted through. As long as the light is not transmitted out of the building it ultimate ends up being absorbed. 100% of the light is converted to heat in this way.

  4. Conventional tungsten incandescent bulbs are about 20% heat efficient; so with a 100 watt bulb, 80 watts will end up as heat.

    Conversely, CFLs are at best about 70% heat efficient.

    In terms of light output, you get about 15 lumens per watt from incandescent (or a better measure, about 13 lux per watt). CFLs get as much as 60 lumens, or 50 lux per watt; though 55 and 45 respectively are more typical.

    20 watt cfls put out 90-95% the light output as 75 watt incandescents. 25 watt CFLs about 90-95% the light output as 100 watt incandescents.

    All those numbers are gross wattage not effective wattage though; which means they don’t account for waste heat.

    The effective wattage of a 100 watt incandescent is about 20 watts. The effective wattage of a 25 watt CFL is about 18 watts. Funny enough, that means their light output per effective watt is essentially identical (within 3%); the difference being the massive waste heat from incandescent bulbs.

    The most efficient gas furnaces are about 85% efficient in terms of thermal energy due to ducting and exhaust losses (their theoretical efficiency is over 90%). Another 15% minimum is lost in the forced air convection and conduction.

    Electric heating is notionally 100% efficient, in that all the electricity funneled into the heating element becomes waste heat; but that’s a theoretical efficiency. Realworld, about 15% of the juice doesn’t end up as radiated heat; and convection and radiation are inefficient at distributing the heat; losing another minimum 15% in air handling.

    So, best case, about 70% of the energy ends up as effective heat… and if you put a fan behind a 100 watt bulb, about 65% of the energy ends up as effective heat.

    The average American home uses 18-24 light bulbs (numbers vary depending on who you listen to); and the average bulb is 75 watts. That’s about 1200 watts of effective radiated heat.

    Of course the average home furnace in the US has an 60,000 BTU capacity, or about 18KW; for an effective heat capacity of about 12,500 watts.

    So 10%… if you put a fan and reflector behind every bulb in your house and ran them all at once.

    Of course the average home AC unit only has a 48,000 or so BTU capacity; and an effective 70% efficiency; about 9800 watts.

    So your light bulbs lose you about 12% of your cooling.

    That was a fun little intellectual excercise.

  5. Don’t care about the relative heating capabilities of the cfl versus incandescent. What I don’t like about cfl is that they have a much “colder” luminescence – not to mention the 60Hz flicker.

    And don’t bother telling me I can’t see it, I can, and so can the wife. The white light doesn’t warm a room the way the red from the incan does. Additionally, cfl’s will not last as long as an incan if they are in a high on/off area, especially now that most of them are being made in China.

  6. I was under the assumption that most people knew that X Watts consumed results in X Watts heat production (to within several decimal points at least). Whether you’re interest is in making heat, light, sound, or motive force, a joule consumed is a joule that ends up, one way or another, as heat, with only some very insignificant exceptions. Therefore you can leave your lights, or anything else inside your heated space, turned on day and night during the heating season without losing any energy, compared to diligently turning off lights and things.

    To put it more simply; during the six to eight months of the year we heat our homes, inside-appliance efficiency and turning things off when you leave the room, etc., are dead moot. Sure– you want an efficient furnace. After that, all that matters is the amount of energy that’s allowed to escape the living space.

  7. If we want to discuss this on a global scale, there are other issues. Electric heat is said to be near “100% efficient”, but that’s only considering what happens inside your house. We are now being told that approximately 50% of electrical grid power is lost in transmission (I saw that in an IBM ad just tonight). Then there’s the efficiency of the generating station, then there’s the energy spent in building the generating station, the energy spent in supplying it with fuel, etc.

    Ethanol production is said to be around zero percent efficient (planting, harvesting, processing and distilling it require as much energy as the completed product contains). After transporting it to the filling station and running the gas pump then, you’re already in the red by the time it reaches your intake manifold. What happens after that is less important if we’re all concerned about global issues.

    Of course, none of that alters the conclusion in the main post. In physics, we use the term “all else being equal” a lot, so we can focus on one problem at a time. All else being equal, you can leave your lights and most appliances on all winter and it won’t make a lick of difference in your energy consumption.

  8. If you are running a heat pump instead of a more conventional furnace then you can achieve greater than 100% efficient use of your electricity under many circumstances.

    Another reason the naggers could have a point is if you want to include the loss of the light bulb life. A light bulb turned off won’t have to be replaced as soon as one you leave burning 24×7. The furnace life is probably not going to be materially affected by leaving the lights on.

  9. You may be right, but the nags aren’t smart enough to figure out that much. Filament bulb life is shortened by more cycling on and off, such that you’ll get more total heat output (more total hours of operation) if you leave it on. Or so I assert. You’ll have to replace it more often, maybe (see below) it’s true, but now we’re countng pennies. Also I notice that bulbs mounted close to a heavy door, or any other source of vibration, have a much shorter life. When the filament is rattled by the closing of the door, it is physically stressed and it breaks sooner.

    I wonder why there aren’t more LEDs used in home lighting, now with the high output jobbies used in flashlights. Wouldn’t they nuke both tungsten and CFs total lifespan? Sure, their spectrum sucks, but I would think that using a variety of colors in an array could make for a decent enough output. You couldn’t heat your house with them, but they’d last for years and years.

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