An LED works when electric current passes through a semiconductor and releases energy as light.
How it works
An LED (light-emitting diode) has a semiconductor with two layers. When current passes through, electrons meet holes at the junction and release energy as photons.
Color
The semiconductor material sets the color: gallium nitride makes blue, gallium arsenide phosphide makes red.
Advantages
- Uses about 75% less energy than incandescent bulbs.
- Lasts up to 25,000 hours or more.
- Little heat and fast switching.
White LEDs often use a blue LED with a phosphor coating.
Semiconductor basics
An LED (light emitting diode) is a semiconductor with a p-n junction. When current flows, electrons recombine with holes in the junction and release energy as photons. This is called electroluminescence.
Color and materials
The color depends on the energy band gap of the material:
- Red and amber: aluminum gallium indium phosphide.
- Green: indium gallium nitride or gallium phosphide.
- Blue: indium gallium nitride.
- Infrared: gallium arsenide.
The 2014 Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for the invention of efficient blue LEDs, which enabled white LED lighting.
White light
White LEDs usually use a blue LED with a yellow phosphor coating, or combine red, green and blue LEDs.
Efficiency
LED bulbs use at least 75% less energy than incandescent lighting and last up to 25 times longer, according to the US Department of Energy. A typical 9 watt LED bulb gives about the same light as a 60 watt incandescent, around 800 lumens.
Lifespan
Many LED bulbs are rated for 15,000 to 50,000 hours. LEDs do not burn out suddenly but dim gradually.
Heat
LEDs produce little infrared heat in the beam, but the base generates heat that needs a heat sink for long life.
Other uses
Displays, TV backlights, indicator lights, car headlights, grow lights and remote controls.
Savings
Replacing the 25 most used bulbs in a home with LEDs can save hundreds of dollars over a few years, according to the Department of Energy.
Semiconductor physics
An LED (light emitting diode) is a semiconductor with a p n junction. When voltage is applied, electrons from the n side recombine with holes on the p side, and each recombination releases energy as a photon. The material’s band gap decides the color: gallium arsenide phosphide gives red, and indium gallium nitride gives blue and green. White LEDs usually use a blue LED coated with a yellow phosphor, such as YAG, which converts part of the blue light. The development of the efficient blue LED earned Isamu Akasaki, Hiroshi Amano and Shuji Nakamura the 2014 Nobel Prize in Physics.
Efficiency and lifetime
The US Department of Energy says residential LED lighting uses at least 75 percent less energy and lasts up to 25 times longer than incandescent lighting. A typical LED bulb produces 80 to 100 or more lumens per watt, compared with about 15 for incandescents. Lifespans are commonly rated at 15,000 to 50,000 hours. LEDs run cooler, but their electronics and heat sinks must manage heat, which is the main factor limiting life. They are directional, instantly start, and many can dim with a compatible dimmer. A 9 watt LED equals about 60 watts of incandescent output.
Based on data from the US Department of Energy and the Nobel Prize organization
