People often tout the energy saving potential of CFLs and LEDs. To really understand how much energy a light bulb saves, however, you have to do what is called a life-cycle analysis. Going backwards from the consumer, you have to transport the light bulb to the store, you have to manufacture the light bulb, you have to transport the necessary materials to the factory, and you have to mine or produce the materials. All of that requires energy. CFLs and LEDs save energy in your house, but what about to manufacture? What about to transport?

In 2011, the Department of Energy conducted a life-cycle energy comparison of incandescent bulbs, CFLs, and LEDs. LEDs were rated to last 20 million lumen-hours in 2011, so they calculated all the energy consumed in manufacturing, transporting, and using these three types of light bulbs to produce 20 million lumen-hours of light.

The results are shown in the graph at right. In 2011, CFLs and LEDs saved almost 3/4 of the energy consumed by incandescents, and by 2015 they are projected to save about 7/8. The energy used to transport all of the lamps turned out to be a trivial part of the total life-cycle energy consumption, you can barely see it in the graph. For incandescents, so was the energy used to manufacture them. For all of the lamps, the real energy went into using them.

The total amounts of energy saved are surprising: in 2011, one CFL would have saved 11,191 megajoules of electricity compared to incandescents, while one LED would have saved 11,257 MJ. Converting megajoules to kilowatt-hours, the unit used on our electricity bills, the savings would have been 3,109 kWh per CFL and 3,127 kWh per LED.

The average home in Missouri used 1,112 kWh of electricity per month in 2011. Thus, replacing 1 incandescent with either a CFL or LED would save enough energy to power the average Missouri home for almost three months (2.8 to be exact). There are 2,723,415 households in Missouri, so if every household in Missouri replaced just one incandescent bulb with a CFL or LED, the total energy saved would be 8.5 billion kWh.

Sources:

Life-Cycle Assessment of Energy and Environmental Impacts of LED Lighting Products, Part 1: Review of the Life-Cycle Energy Consumption of Incandescent, Compact Fluorescent, and LED Lamps. Navigant Consulting for the Solid-State Lighting Program, Department of Energy, August 2012. http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/2012_LED_Lifecycle_Report.pdf.

For energy consumption of average Missouri home: Table 5A. Residential Average Monthly Bill by Census Division, and State 2011. Energy Information Administration, http://www.eia.gov/electricity/sales_revenue_price/xls/table5_a.xls.

For number of households in Missouri: State & County Quick Facts: Missouri, U.S. Census Bureau, http://quickfacts.census.gov/qfd/states/29000.html.