AskPablo: Lightbulb Philanthropy

Image Courtesy of Stoughton UtilitiesAre you concerned about your contribution to the climate change crisis? Are you still unsure about carbon offset programs? Well, you are not alone. While I am a strong believer in the value and importance of offset providers such as DriveNeutral and Native Energy I also realize that there are some organizations out there, whose carbon offsets might not be as verifiable or that take too much profit for themselves. If I can’t convince you to offset your emissions with a legitimate offset provider I would certainly like to help you to neutralize your climate impact in another way.


Here is the idea: You get together with your friends and collectively replace all of your wasteful incandescent light bulbs with efficient compact fluorescent lights (CFLs), using your collective buying power to get a good deal. Then, after rejoicing about all the energy (and $$) that you have saved you figure out your remaining carbon footprint. You then buy CFLs for low-income families in your neighborhood or people that would otherwise not buy CFLs (because of their higher initial cost). Since those households would not have otherwise switched to CFLs you can take credit for the carbon emissions reduction and bam! you can consider yourself offset! And as an added bonus you will help a low-income family save money on their electricity bill!
But how many bulbs would you need to buy?

  • A 15 W CFL replaces a 60 W incandescent and its median lifespan is 10,000 hours.

  • So a savings of 45 W over 10,000 hours = 450 kWh, or 0.45 MWh.
  • In California the grid emits 0.51 metric tons per MWH (find your state in CCX Advisory 2007-01)
  • One bulb (in CA) would prevent the emission of 0.223 mT (0.45 MWh x 0.51 mT/MWh) or 223 kg (492 lbs) of CO2.

If your car emits 5 mT/year, you would need to buy 23 bulbs (5.0 / 0.223) for your neighbors to offset its emissions for the year (Calculate your annual vehicle emissions using this calculator or see my column on vehicle emissions: AskPablo: The Tailpipe Mystery.
To calculate you household carbon emissions take a look at your electric bill. Add up the kWh used in the last 12 months (if you have records that far back, otherwise multiply the last month by 12 to get a rough estimate) and divide by 450 kWh to get the number of bulbs you should buy.
There are many calculators out there that will do all the hard work for you. One that I like is the US EPA’s Personal Emissions Calculator. The following bullet points will help you calculate the number of bulbs to buy based on your result from the EPA calculator.

  • To convert pounds to metric tons multiply by 0.454 to get kg, then divide by 1000 to get metric tons of GHG emissions.

  • Next, find your state’s grid emissions factor (in CCX Advisory 2007-01) and multiply it by 0.45 MWh (the energy saved over the lifetime of one CFL). This gives you the GHG emissions prevented by one CFL, based on your state’s power generation emissions.
  • Now divide the result from the EPA calculator (in metric tons, from bullet point one) by the result from bullet point two. This should give you the number of bulbs that you need to purchase (each year) to offset your household’s GHG emissions. Always round up and remember to recalculate your emissions each year to see if you have reduced your climate impact.

I hope that you have fun with this and it helps you build a community of energy efficient climate leaders! Please submit your success stories, comments, or questions in the comments area below. Thanks for reading AskPablo!
Pablo Päster
Sustainability Engineer