From Wikipedia, the free encyclopedia
In the US, one kilowatt-hour (3.6 MJ) of electricity currently causes an average 1.34 pounds (610 g) of CO 2 emission. Assuming the average light bulb is on for 10 hours a day, a 40-watt bulb will cause 196 pounds (89 kg) of CO 2 emission per year. The 6-watt LED equivalent will only cause 30 pounds (14 kg) of CO 2 over the same time span. A building’s carbon footprint from lighting can therefore be reduced by 85% by exchanging all incandescent bulbs for new LEDs if a building uses only incandescent bulbs.
In practice, most buildings that use a lot of lighting use fluorescent lighting, which has 22% luminous efficiency compared with 5% for filaments, so changing to LED lighting would give only 34% reduction in electrical power and carbon emissions.
The reduction in carbon emissions depend on the source of electricity. Nuclear power in the United States produced 19.2% of electricity in 2011, so reducing electricity consumption in the U.S. reduces carbon emissions more than in France (75% nuclear electricity) or Norway (almost entirely hydroelectric).
Replacing lights that spend the most time lit make the most savings, so LED lights in infrequently used rooms bring a smaller return on investment.