Friday, June 30, 2006

CO2 Emissions: Light Bulbs vs. Cars

I was surprised that the first suggestion to reduce greenhouse gases on the Climate Crisis Take Action Flyer was to change your light bulb. So, I became curious, how much CO2 emissions would changing a light bulb save?

I read part of this report and was surprised again, this time to see that CO2 emissions from electricity generation are larger than transportation. Electricity production creates 2,337.8 Tg CO2 Eq. (33% of total emissions) vs. 1,955.1 (27%) for transportation (total emissions of 7,074.4). Residential electricity is about 33% of total electricity (another approximately 1/3 for industrial and 1/3 for commercial) for 701 Tg and 40% of transportation is for personal use automobiles (based on data in this report) for 782 Tg. For the average American then, personal residential electricity use and personal automobile use have about the same about of carbon emissions.

Also note that for every 1 kWh of electricity you use at home, there are 2 kWh being used by businesses to create and sell you the products and services that you buy. The emissions caused by the purchases you make therefore can have a larger impact than the electricity and gasoline you use purchase directly.

I decided to investigate, how much CO2 do light bulbs emit, how much could I save, and how would it compare to buying a more efficient car?

From the EIA, we find the pounds of CO2 emissions per kWh of electricity produced by various fuel sources in 1999:
2.1 Coal
2.0 Petroleum
1.3 Natural Gas
0 Solar, Wind, Hydro, Nuclear
1.3 Average for all forms of generation in US

A gallon of gasoline emits 20 lbs of CO2. 10 kWh of coal based electricity (at 2.1 lbs/kWh) emits about the same as a gallon of gasoline. Or put another way, running a 100w light bulb for 100 hours emits the same amount of CO2 as 1 gallon of gas. I use the coal value because it is most likely that new power plants will be coal based. If you reduce your usage, on the margin it will help to stop new coal plants from being created. If instead you used the average for all forms of electricity generation value of 1.3 then 15 kWh emit the same as a gallon of gasoline.

A 100w light bulb that is run 3 hours a day every day will use around 100 kWh a year. A high efficiency light uses about 1/4 the electricity of a normal bulb. Replacing it with a 25w Compact Fluorescent Bulb would save 75kwh a year. This would be 150 lbs of co2 or the same as 7.5 gallons of gasoline. Not bad for just replacing one bulb.

According to the EIA, the average US household uses 10,000 kWh a year of which 8.8% is lighting or 940 kWh. This EIA report also looks at lighting usage and comes to a similar figure.

Emissions from lighting use is 940 kWh * 2.1 ~ 2000 lbs co2 or the equivalent of 100 gallons of gasoline. The savings for a standard household changing all their bulbs would be around 940kwh * .75 = 705kw * 2.1 = 1500 lbs of co2 or 75 gallons of gasoline. That is a pretty good savings.

For comparison, if you drove 12,000 miles a year and upgraded from a car that gets the national average of 20 mpg to one that got 30 mpg, you would save 200 gallons or 4,000 lbs of co2. Upgrading from 30 mpg to 37 mpg would save 75 gallons a year, or the same as upgrading all the light bulbs in a standard home. In general, I think there are larger savings to be had from changes in using your car, but the savings from the light bulb are still sizable, and in most cases much easier and cheaper to accomplish.

On a global scale, the lighting has a large impact as this BBC article reports:

"Nineteen percent of global electricity generation is taken for lighting - that's more than is produced by hydro or nuclear stations, and about the same that's produced from natural gas," he told the BBC News website.

The carbon dioxide produced by generating all of this electricity amounts to 70% of global emissions from passenger vehicles, and is three times more than emissions from aviation, the IEA says.
In the US we drive more and use comparatively less electricity for light, so cars have a larger impact vs. lighting for the average American, but worldwide the savings from higher efficiency bulbs looks large.


Anonymous said...

I am so grateful for this site because I am doing a presentation on CO2 emissions from lightbulbs. Thank you so much for the time you put into this!!!

Fat Knowledge said...


Glad to hear it was helpful, hope your presentation goes well.

Anonymous said...

A close friend of mine was bragging how green he is because he changed all 200 lightbulbs in his new house to CFLs. Of course, he was promptly ridiculed for HAVING 200 lights in his house. His Energy Star house is 2900 square feet. Do you know how much of a difference he'd see in energy use if he did everything the same (still 3 people in the home taking the same number of showers, washing the same amounts of laundry, etc.) but with a home only 1900 square feet? Do you know what the average energy use of a 2900 square foot home is to a 2900 square foot Energy Star home? Knowing an average number of light bulbs to have the house would be interesting too... Thanks!

Fat Knowledge said...


Yeah 200 lightbulbs is a lot. And I figure that if you replace just the lights that you keep on for at least 3 hours a day that you get 95% of the benefit.

I don't know what the average energy use of a 2900 square foot home is. Just that the average American household uses around 10,000 kWh a year, 940kWh or 8.8% is for lighting.

I also have no clue how many lightbulbs that would be, but 940kWh would be like 8 100W lightbulbs on for a little over 3 hours a day, or a little more than 1 100W lightbulb left on 24 hours a day for a year.

AK said...

nuclear energie emits CO2!! the genaratoruses coal +it takes about 2 gASTRIQUE TONNES OF co2 TO BUILD IT!!!!!!

Alagesan said...

could i know why these emission takes place and that process involves?

Anonymous said...

Thanks so much for the info!

Anonymous said...

Im doing a presentation on this as well, this was really helpful! thanks!!

MIBearings LLC said...

An old post, but I thought I'd point out that the "average for all forms of electricity generation" needs to be a weighted average rather than an aggregate average value of 1.3. The weighted average is around 1.5
You can do the math yourself from data here.

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