Which Light Is Greenest?

Suppose a light bulb burns out in your house and you want to replace it with the most environmentally sustainable option. Compact fluorescent lights (CFLs) and light-emitting-diode bulbs (LEDs) use about 75 percent less energy than a comparable incandescent light bulb. Sounds like a no-brainer to use a CFL or an LED, right? Not necessarily. A common outcome of life cycle assessments on everyday objects is that Item 1 is better than Item 2 at helping to alleviate one problem (for example, global warming), but the order is reversed for a different environmental problem. In other words, the best choice depends on what problem you are most interested in mitigating.

A recent analysis of light bulbs published in Environmental Science and Technology demonstrates this point. (1) The study found that CFLs and LEDs contain toxic metals such as lead, copper, and zinc. On the basis of an analysis of their toxicological impact, the investigators determined that both CFLs and LEDs upon disposal would be classified as hazardous waste under U.S. EPA and California regulations. In contrast, the incandescent bulbs would not be classified as hazardous waste. Furthermore, the study found that if CFLs and LEDs are used to replace incandescent bulbs, we will deplete valuable metals such as silver, gold, antimony, and copper at a faster rate than we currently do.

What makes these results even more unsettling, however, is that for technical reasons, author Julie Schoenung and her team were not able to include the impacts of mercury in their analyses. Although manufacturers are working hard to decrease the amount of mercury in CFLs, studies show that when a CFL bulb breaks, the amount of mercury vapor in a room exceeds OSHA standards, at least temporarily.

Choosing the environmentally most sustainable light bulb involves deciding whether energy use is a bigger environmental concern than toxicity or resource depletion. Ideally, we should be able to exploit the energy-saving aspects of the CFL and LED bulbs while also minimizing their toxicity and resource depletion potentials by recycling these bulbs.

—David Tyler

Explore the life cycle of a CFL bulb with Sourcemap 

1. Lim, S. 2012. Environmental Science & Technology doi:org/10.1021/es302886m.

David Tyler is the Charles J. and M. Monteith Jacobs Professor of Chemistry at the University of Oregon.

Photos (left to right): ©Africa Studio/shutterstock, ©Polryaz/shutterstock, ©Junichi Suzuki/123rf

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2 Comments

  • Michael Grossman March 20, 2013 at 7:32 am

    “Choosing the environmentally most sustainable light bulb involves deciding whether energy use is a bigger environmental concern than toxicity or resource depletion.”

    This is a vague and waffly conclusion, essentially comparing apples and oranges. Toxic materials can be recycled, but it requires energy. A more meaningful comparison is the total energy used in the production, useful lifetime, and recycling of both products.

    So suppose you run a CFL at 20W for 10,000 hours. (This is about the middle of their stated lifetime.)

    20 J/sec X 2600 sec/hr X 10,000 hr = 720 megajoules of energy

    A 60W incandescent run for the same length of time would, just as irreversibly, convert 3X as much energy–conveniently packed into atomic or chemical bonds–into disordered energy in the form of light and waste heat:

    2160 megajoules.

    (Note that you’ll probably go through 3-5 incandescent bulbs to get 10,000 hrs runtime. Let’s just say it takes 4.)

    Does the energy required to produce, use, and recycle one CFL exceed that of going though (conservatively) 4 incandescents to get the same runtime?

    Let X be the energy required to produce and dispose of four 60W incandescents.

    Let Y be the energy required to produce and dispose of one 20W CFL.

    Quantitatively, then, is ( Y + 720 ) greater than (2160 + X)?

    Let’s assume it is and write

    ( Y + 720 ) > (2160 + X)

    Simplifying, we get finally get down to a meaningful criterion:

    (Y – X ) > 1440

    In words, if the energy used in production and disposal of one CFL minus the energy used in production and disposal of 4 incandescents exceeds 1440MJ (the energy profit of running the more efficient CFL), we’re all better off sticking with incandescents.

    Too bad it doesn’t say on the box what X and Y are. Perhaps someone can find out.

    Reply

  • Mackenzie March 27, 2013 at 1:43 pm

    I remember my biology professor asking if we’re all familiar with the concerns about mercury in fluorescent lights like CFLs or the ones in our classroom. He then asked how many of us were aware that dead batteries should not be disposed of in regular trash. (Answer: very few) Then he pointed out that the amount of mercury released when the battery-containing trash is incinerated far outstrips the small amount released if you drop a lightbulb.

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