Five Percent: Conserve Energy

Climate Change Is Important: Energy Conservation is the First Step

October 27, 2007

2.6% Reduction of CO2 … Just from one CFL lightbulb?

If every one of the 110 Million households in the USA changed just one light bulb to CFL, this would reduce the total output of CO2 emissions in the United States by around 2.6%. Do I have my math right? What assumptions are going into this. It seemed kind of implausible, to be honest. But I think the numbers check out. Have I made an error?

So first, read the What You Can Do page of the Inconvenient Truth website, which claims:

If every family in the U.S. made the switch, we’d reduce carbon dioxide by more than 90 billion pounds!

Now consider the following image, produced by the US Department of Energy’s “Carbon Dioxide Information Analysis Center” which produced this data: .

In 2003, we produced about 130 teragrams of CO2 per month. If we’re talking about the same CO2, then it’s pretty easy math to see what share of that 130 Tg/month comes from the 90 billion pounds of CO2 saved.

Ok, first, what’s 130 x 12 teragrams in pounds: answer from Google is 3.43921129 × 1012 pounds per year. So what percentage of this is the 90 billion pounds saved? Just ask Google: 90 billion / (3.43921129 × 10^12) in percent? Answer: 2.62 percent.

Minor conclusion: Google’s calculator is awesome!

Main conclusion: If we all changed one light bulb to CFL, we would reduce carbon emissions by 2.6%. Holy mackerel!

Source and Assumptions

This page from Greenlights USA, seller of Compact Fluorescent Bulbs (CFL) does a great job of showing how they arrived at a similar (larger, actually) result for the 90 Billion Lbs CO2 claim. All of their sources are from US government measurements, and are conservative, if only because they are outdated. The same conclusion is reported on the Energy Star website.

Ok, so one key assumption of this calculation may be questionable. 101 Billion kWh of electricity were used for residential lighting in 2001. If you change an incandescent bulb, it has to be one that represents at least an average use of light in your house — the bulb I replaced in the utility room that I turn on for five minutes every week or two doesn’t really count. The ones in our bedroom, living room, and office, outdoor floods and the basement playroom are certainly in the normal use zones. So, make your bulb count. Or better yet, recognize that not everyone is going to replace a bulb, so maybe do three or four (or 15 – 20, which we did).

The graph above, is from a US Government agency, the CDIAC details of their carbon dioxide emissions study are here. My estimate of 130 teragrams is probably low, since it’s from 4 years ago.

The only thing I am not sure about here is whether the CO2 emissions are comparable. But I think so. Please let me know if I have made an error.

So if this is right, that’s a damned impressive statistic.


  1. […] just one example of a bridge technology. Environmental control systems for buildings are another. Compact Fluorescent bulbs are another. Water saving shower heads, toilets, and faucets are others. They are […]

    Pingback by Why the iPhone (actually) Matters | Five Percent: Conserve a Little Energy — May 18, 2008 @ 5:09 pm

  2. The problem is that the site does not specify the time period over which the 90 billion pounds is saved. It could be the life-time of the CFLs, in which case your estimate would be inaccurate.

    Comment by Jedidiah Marquette Williams IV — June 25, 2008 @ 12:43 pm

  3. Jedidiah — I think you’re right. The “What Can You Do” page linked above has the following statement:

    This simple switch will save about 300 pounds of carbon dioxide a year. If every family in the U.S. made the switch, we’d reduce carbon dioxide by more than 90 billion pounds!

    If there are 110M households (which might be equivalent to “families”) then indeed, the savings is 33 Billion pounds per year. So I guess the claim assumes the lifetime of the bulb, as you suggest.

    So again, assuming my math is right, the annual savings is a more modest 0.8% per year. And as I re-read my post, I see that I didn’t normalize the 2.6% claim for time, thus suggesting something incorrect. My bad — the same one that is strongly implied in the quote above.

    Thank you for correcting my error!

    Comment by Tom Harrison — June 25, 2008 @ 1:21 pm

  4. CFLs do use less energy compared to an incandescent or flourescent bulb, but do you know that if this “eco-friendly” bulb happens to break or is not disposed of correctly, it exposes the environment to dangerous amounts of mercury, costing the consumer $2,000 to get rid of this toxin from their home.
    If you are looking for an eco-friendly bulb that is good to the friendly bulb then I recommend you change to an LED bulb. This bulb is 100% energy efficient, producing no heat and therefore using less watts to produce the same (if not brighter) light. Not only do they not eat out your electricity bill but they also last for up to twice the amount of any CFL. Most CFLs last around 6,000 hours but an average LED will last you from 16,000 to 50,000 hours meaning you don’t have to buy replacement bulbs (saving you gas and the air pollution your car would release to the trip to the retail store).
    Most people don’t like LEDs because they are costly but do not turn this bulb just because of the shelf price. Since this bulb lasts longer while using less wattage, it actually saves you money compared to the money you use for other bulbs such as CFLs. The cost of maintaining CFL bulbs over 60,000 hours would cost you around $900 but using LED bulbs for 60,000 hours would only cost around $450.
    This bulb will help you during this economy and it will also help the environment.

    Comment by Ritwika — January 10, 2010 @ 8:44 pm

  5. Ritwika —

    Your assertions are false and are the worst, and least helpful kind of commentary I can imagine. Normally, I just delete such useless drek, but tonight, I feel like responding. So brace yourself.

    The mercury notion with CFLs is understandable, but completely baseless. No doubt, mercury is a hazardous substance. And yes, CFLs have mercury. But take a deep breath — yes, in that deep breath, if you are like 80% of Americans, contains mercury vapor released as the result of burning coal to make electricity. A typical CFL uses 1/5th the electricity of an incandescent bulb, and since a large portion of US electricity is made from burning coal, reduces the amount of mercury in our atmosphere. And the facts are that even several years ago, when CFLs had 5mg of mercury, if every one sold were broken and released into the atmosphere, it would be less than what would have been released had we not replaced incandescents with CFLs.

    Today, CFLs use less than 1/2 as much mercury, an amount that would be described as trivial. And CFLs quality is higher. And … just checking, how many CFLs have you broken in your lifetime?

    $2,000 to clear the air? Why? EnergyStar says “open the windows” and “be a little careful”. Please, a citation from a credible source for that claim would be appreciated.

    Mercury is not something we want in our systems. But it’s not plutonium, and it’s not cyanide (which, by the way, exists in the seeds of apples). It’s one of a huge array of toxins known to be bad, and not, sadly the worst or most caustic.

    Please, don’t sell LEDs as anything other than a superior technology. But also, please don’t tell me they are a realistic alternative for most people, today, compared to incandescent or CFL bulbs.

    Sure, LEDs cost less to run, but as we saw with CFLs, lifespan estimates are suspect to start. Most CFLs fail not because their stated lifespan has been reached, but because the ideal conditions for which their electronic ballasts are engineered do no exist. LEDs are also sensitive electronic devices, and none have been around long enough for anyone to realistically assess their lifetime claims. To be sure, LED is a more resilient and contained technology, and in some ways has a far less steep hill to climb than CFL, but after several years, LED is still only practical in a few applications (nightlights, Christmas-tree bulbs, and a few well-engineered PAR-30/38 replacements).

    I am the first to agree that CFLs are far from the ideal technology. LED certainly shows promise and every year, manufacturers are making a wider range of products that suit our needs and at lower and lower prices.

    But let’s be real. LED is still far, far more expensive (up front), perhaps 10x more, in most applications, than CFL or incandescent. Do you have $100 per light to spend on replacement ceiling lights? It was a stretch for me to spend $8 per lamp to replace 7 incandescent bulbs with CFLs, and worse, they weren’t as good as the bulbs they replaced. LEDs (e.g. from CREE) might be as good as their incandescent equivalents, but they are considerably more expensive.

    LEDs are not even as far along, in most cases, as CFLs — they still have issues with color temperature, brightness, directionality, and price, compared to CFL and incandescent. Yes, there are some application where a long-term cost-benefit analysis would show LEDs to have a lower lifetime cost, but most don’t take into account net present value (NPV).

    NPV can be understood simply by answering this question: if you had the option of $100 now, or $10/year over ten years, which would you take? All rational people would take the $100 now. Yet behavioral economics has shown that people do not behave rationally (and actually one example is in how people over-value risk, such as the “risk” of a CFL breaking, but I digress) — indeed, a classic experiment shows that most people would take $100 now from a trusted source versus the promise of $100 a year for the next 5 years — a decidedly irrational decision.

    So, finding a common ground here — we have a lot of work to do convincing people, on purely economic merits, of the case of any long-term cost-benefit case.

    Solar PV is quite expensive and has a typical packback period of around 10 years or so. For a business, this may be a simple decision — for us flawed humans who calculate risk wrong (“Oh my god, a CFL!!!”) and who calculate benefit wrong (“It will save money over 10 years!!!”), many very rational decisions are non-starters.

    So let’s be real: incandescent bulbs, at $0.60/bulb are the best financial choice today. CFLs, at something like 3x or 4x the cost (and please, don’t buy the cheap versions — they suck) are a stretch, even if they do make economic sense in just a few years.

    LEDs, whose performance is limited to a few specific applications that have indeed proven to be both aesthetically pleasing, and are financially plausible, are practical only for those people for whom the trade-off between a $1 expense now with a high running cost, versus a $100 expense now with a low running cost, and break even at 5 year is a realistic decision.

    Please, please, please: do not add in any irrational, emotional-response based flames about mercury or any other irrelevant factors.

    In the end, none of our idiotic concerns about cost or safety will make a good god-damned iota of difference when the true cost of our consumption-based lifestyles are tallied up.

    Maybe it’s drought. Maybe it’s famine. Maybe it’s flooding. Any of these are foundations for war. But whatever the initial implications, our use of energy today will have its consequences tomorrow. Silly bickering about the relative merits and costs of CFLs vs. LEDs will be utterly pointless in the grand scheme of things.

    So, yes, buy LEDs because it’s right. If you can’t afford them, buy CFLs, and pay no attention to the alarmists who shout about mercury (sorry, that battle was lost when we started burning coal).

    And if you can afford neither, here’s an idea. Turn off a light of any kind. Now.

    Sorry, this is a response that is completely out of balance from the comment. But it’s valid, and real.


    Comment by Tom Harrison — January 10, 2010 @ 11:14 pm

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