NATIONAL GEOGRAPHIC – Energy and Technology
Energy & LED Lights – By John Brennan, Demand Media
New LED lighting options can save energy
Consumer electronic devices using light-emitting diodes range from television remote controls to digital displays. In recent years, LED lights have also become available for interior lighting in homes and businesses. One of the potential benefits associated with LED lights is decreased energy consumption in all of these applications (see References 1, page x).
Diodes are directional semiconductor devices. They contain two sandwiched layers join two types of semiconductors. The p-type semiconductor material creates electron deficiencies or “holes” by removing weakly bound valence electrons. The n-type semiconductor material has an excess of electrons. At the junction between the two layers, electrons from the n-type layer flow into the p-type layer, creating a positive charge on the n-type side and a negative charge on the p-type side, which opposes further current. Connecting the positive terminal of a voltage source to the p-type side and the negative terminal with the n-type side allows current to flow through the LED. The recombination of holes and electrons releases some energy in the form of visible light. (See References 3)
LEDs emit light across a narrow band of wavelengths, so they typically produce colored light. White-light LEDs are the most important kind for interior lighting, however, and these typically shine blue or ultraviolet light onto a special coating, which will re-emit some of this energy as visible light. Other types combine blue, green and red LED chips to create overall white light; these have the potential to be more energy efficient than the phosphor-coating kind, although they are more complex. (See References 1, pages 1-2)
According to the U.S. Environmental Protection Agency and Department of Energy’s Energy Star program, LED lights have the potential to emit more light than either fluorescent or incandescent bulbs. They estimate that incandescent bulbs produce 90 percent of their energy as heat; compact fluorescent light bulbs are more efficient, but still produce 80 percent of their energy as heat. LEDs release the small amount of heat generated into a heat sink behind the diode. (See References 2)
Incandescent and fluorescent light bulbs not only produce most of their energy as heat, but they scatter light in all directions, unlike uni-directional LEDs. This uni-directionality provides additional energy savings, because a conventional bulb in a recessed socket wastes as much as half of the light it produces by scattering it back into the recess, where it does not provide any illumination to the room. (See References 2) Designing LEDs with brightness controls allows dimming when users need less light (see References 1, page 6). According to the U.S. Department of Energy, rapid adoption of LED lighting could reduce lighting electricity demand by as much as 33 percent by 2027 (see References 2). Good design is important, however; poorly designed LED lights can have a short life span and need more frequent replacement, reducing energy savings (see References 2).
1. U.S. Department of Energy: Office of Energy Efficiency and Renewable Energy; Energy Savings Estimates of LEDs in
Niche Lighting Applications; January 2011
2. Energy Star: Learn About LEDs
3. Georgia State University: HyperPhysics: LED Device Structure
About the Author
Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in “Plenty,” “San Diego Reader,” “Santa Barbara Independent” and “East Bay Monthly.” Brennan holds a Bachelor of Science in biology from the University of California, San Diego