Carbon footprint comparison: CFL vs. Incandescent

Ever wondered what teh real eco-benefit is to using CFLs instead of incandescents, which are now being phased out completely for household applications?  Here's my analysis. Feedback welcome. Also, if anyone want to work with me on producing a series of shorts along the lines of  this paper, get in touch! There's a lot of magical thinking around people's "green" behavior.  I'd love to dig into some of these areas a little and demystify things. 

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To compare the now-familiar compact fluorescent bulb to the traditional incandescent bulb, it is important to look at more than just the obvious and much touted difference in energy consumption between the two, which is a well-established difference. Worth examining are not just the amount of electricity used and the amount of lumens emitted per watt used, but also the money spent by the end-user over the life of the bulb, what is necessary to make each of the two different types of bulb, where that occurs, how they all get here, and what happens to them after they’re no longer serviceable.

Here are the two bulbs in question: a Sylvania #12750, 100 Watt, 120 volt frosted bulb, 1710 lumens, 750 hour estimated lifespan, priced at $0.65, and a

CFL Philips lighting #137158, 27 watts, 1750 lumens, 10000-hour lifespan priced at $2.90. 

            The incandescent gives us 17.1 lumens per watt versus the fluorescent’s 64.81 lumens per watt, a clear advantage in energy spent for light gained.  This is not news.

            Also not news is that the incandescent has far superior color rendering.  Incandescent light are what is termed a “black-body lamp”, so called because the light is generated by heating matter, the “black body” in question, up to the temperature at which it glows. Another familiar black body is the sun.  These black body sources distribute light on a smooth curve across the visible spectrum of radiation.  The Color Rendering index uses the light from this other blackbody, the sun, as the source as the benchmark for what constitutes perfect color rendering.  Fluorescents emit light with an uneven distribution across the visible spectrum with spikes in certain frequencies, which we humans find unnatural and unpleasant.

            Assessing the costs over ten thousand hours, the estimated lifespan of the longer-lived bulb, gives us the following results.  Assuming a price of 10.9 cents per kWh, which is what I paid in October 2010, and that the replacement price for the incandescent stays the same as the initial purchase price, .65, it works out to a financial savings of 105$ over the 10,000 hour time span. The CFL uses 27w, working out to 270 kWh over its life, whereas the incandescent uses 1000 kWh over the 10,000 hour time span and needs to be replaced 13.33 times. This replacement factor comes up in every area of examination, that however small the difference between the two bulbs might seem initially, it becomes much greater when multiplied by 13.33.

            As far as the production of the two bulbs is concerned, there are several elements to examine. The first is where are they made and what does it take to get them to the end-user in Brooklyn. Both Philips and Sylvania make most of their bulbs in China, not surprisingly, so one could consider that factor to be equal between the two bulbs.  It might even seem to be an advantage for the incandescent bulb, since by the case, a 100w bulb weighs .096 lb. including packaging, while a 27w cfl weighs .225  lb. including packaging,  only 42% as much.  However, once you include the number of times the incandescent will be replaced, the numbers look much different.  We have 1.28 pounds of incandescent transported from China versus .225 pounds of compact fluorescent, 569% more.

            The next question is what does it take to make each of these bulbs. An incandescent is a glass capsule, a tungsten filament, two nickel-iron lead wires, and a glass-and-aluminum base.            A compact fluorescent is a glass tube, a phosphor coating, some mercury vapor, a filament, circuit-board ballast, and a plastic and aluminum base.

            The process for making an incandescent bulb is as follows: the filament is made by drawing heated tungsten wire through a die, after which it is annealed with heat and wound into its characteristic spiral and treated with acid to remove the mechanism used to make the spiral. The lead-in wires are inserted. The glass casings are made by running a ribbon of heated glass along a conveyor belt, where air nozzles blow the glass into molds that give them their shape. The base is stamped in a mold, the whole thing is put together in a machine, after which it is filled with argon and nitrogen and sealed shut mechanically. Not nothing, but it doesn’t involve as many steps or as much energy as the process for making a compact fluorescent bulb.

            The process to make a CFL is this: The glass is blown into long tubes, which are then cut to length and twisted into a spiral while still heated. The inside of the tube is rinsed with titanium dioxide, pretreated with another chemical, then coated with phosphors on the inside and baked.  The filament is assembled by a machine, then coated with electromagnetic powder, and inserted into the glass tube. The tube is then passed through a torch-like machine to remove impurities and the inside is rinsed with argon. Then the mercury is vaporized and injected into the tube. The circuit board ballast is printed, and then glass, filament and circuit board are glued into a plastic and aluminum base.

            The manufacture of both bulbs is a complex industrial process, but from the preceding paragraphs, it is clear that CFL manufacture has more steps and more heat-based processes, not to mention a higher end-user price, showing us that CFL manufacture is more energy- and material- intensive than incandescent manufacture.

            The incandescent uses about a third less glass than a CFL, about 9 in²  versus about 25 in², since the simple bulb has much less surface area than the long corkscrew shape, and they both use roughly the same amount of aluminum in the screw base, but the incandescent loses out even in these areas because of the one-thirteenth length lifespan.  119 in² used for the incandescents, 25 in² for the CFLs.

            In the area of side effects of manufacturing, the incandescent rises slightly in comparison.  There is nothing particularly toxic in incandescent bulb manufacture, other than the processes necessary to get the raw materials of aluminum, glass, nickel, iron, tungsten, argon and nitrogen, many of which materials are also used in the CFL.  The process of manufacturing CFLs is certainly more of an environmental concern based on the following data.

Not all CFL bulbs comply with the E.U. Restriction of Hazardous Substances of 2006 standard for manufacture of electronics, which bans the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated biphenyl ether.  Therefore, some of them are still made using these extremely toxic and long-lasting chemicals. Another piece of evidence, albeit circumstantial, is that compact fluorescents are almost entirely manufactured in developing nations with lax environmental regulations, such as China and India. One reason they are cheaper to make them there is the lack of environmental laws.  So as far as toxicity of manufacturing process is concerned, the incandescent is the clear winner.

            Toxicity brings us to the topic of mercury, which is the one negative issue people may have heard raised in connection with compact fluorescents. Mercury is a high-profile toxin. Many U.S. states have a fish consumption advisory due to the presence of mercury in fish. Mercury is highly toxic to the central nervous system and the kidneys and it is estimated that up to 10% of all children born in this

country are at risking of having impaired neurological development due to

mercury. It is no longer mined in most industrialized countries because it is too locally toxic, too expensive on account of environmental protection laws, politically unpopular, or all of the above.  Currently, the main producers of mercury are China, Kyrgyzstan, Mexico, and Algeria, none of whom is noted for having strong environmental protection laws.  Spain, formerly a major producer, has recently discontinued mercury mining.

5 mg of mercury per bulb is the current DOE Energy Star rating guideline for mercury content of compact fluorescent bulbs, but that is only for bulbs compliant with that standard, and some other CFLs claim to have significantly less than 5 mg mercury in them.  The bulb we are using as our example is Energy Star compliant, so we will assume that it contains 5 mg of mercury.  At this point, it looks like the incandescent is clearly ahead of the CFL because no mercury is involved at all in its manufacture versus 5 mg for the CFL.

Important to take into account here is that mining for industrial use is not the only source of environmental mercury. Emissions from coal-fired power plants are a major source, approximately .0234 mg of mercury per kWh of electricity generated. America gets approximately 45% of its electricity from burning coal, so if we take 45% of the 1000 kWh to be used by the incandescent, we get 23.4 mg of mercury lofted into the atmosphere by our incandescent.  For the CFL, the number is 6.318 mg of mercury released by the electricity consumption and 5 mg contained in the bulb, totaling 11.318 mg of mercury.  Again, the CFL is ahead, even on mercury.

There is the question of how much the CFL is ahead on mercury, because we don’t know if the 5 mg inside the bulb will be released into the environment or recycled.  When compact fluorescents are thrown away with regular garbage, they are generally tossed in a landfill, where they break, or are incinerated, where they also break.  Obviously when they are incinerated, their mercury enters the atmosphere, but when they are landfilled, some of the mercury still leaches out horizontally in gaseous form.  Let us consider landfills to be part of our environment in the long term, and say that when mercury is thrown in a landfill, that mercury can be considered to be in the environment.

Three studies done in Maine brought back CFL recycling rates of 2%, 6.7%, and 23.5%.  Until better data becomes available, we’ll use the average of those three results, about 10%.  Subtracting 10% from the 5 mg contained in the CFL bulb, we have a final mercury scoring of 10.818 mg mercury for the CFL and 23.4 mg of mercury for the incandescent, (provided that the end user is not one of those people who pays the extra money to get all of their electricity from renewable sources) still a clear advantage to the compact fluorescent.

Beyond mercury, we have to consider mass entering the landfill, which is similar to the earlier transportation topic.  After the mercury from a CFL is reclaimed, the rest of it goes into a landfill, as does a traditional incandescent bulb at the end of its life.  Per ten thousand hours of illumination, we now have .225 pounds of compact fluorescent going into a landfill or incinerator, less a negligible amount for the 5 mg mercury removed, versus 1.28 pounds of incandescent. 

To summarize, here are the differences between the two bulbs. Incandescents look nicer and are cheaper and less toxic to make, but not when you consider that you need thirteen times more of them.  Compact fluorescents have a more complex, toxic and energy-intensive manufacture process, and do contain mercury that could end up in the end-user’s immediate environment, but because they last so much longer than incandescents, they come out ahead on all counts.  When that lifespan multiplier, a factor of more than thirteen, is taken into account, they cost the user less in the long run, they give more light for the amount of energy used, they use less resources in their manufacture and transport, and they take up less space in landfills or capacity in incinerators.

The concerns with compact fluorescents that must be kept in mind are ones of toxicity.  One should make sure to buy compliant CFLs (the TCP brand is an example), and be sure to recycle bulbs that no longer work to avoid depositing that mercury in one’s own immediate environment.  Energy Star’s savings calculation spreadsheet also has some nice green bromides further encouraging you to use them.  They state that replacing one 100w incandescent with a 27w CFL is the equivalent of taking one tenth of one car off the road for a year, has the equivalent air pollution reduction of 1/8 of an acre of forest, and will save putting 1150 lbs of carbon dioxide into the atmosphere.

yours

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