LED Light

• LEDs are built from tiny semiconductor chips, similar to computer chips.Photodisc/Photodisc/Getty Images
  
  In contrast to incandescent bulbs or fluorescent lights, LEDs create light from a semiconductor chip. The chip is made out of two slightly different materials layered on top of each other. Each material keeps its electrons at different energy levels, so when electrons get pushed from one side to the other, they gain energy, which they can show up as light. Because the wavelength of light is dependent on its energy, these chips are built with one specific energy difference, which means one specific wavelength.
  
  

Material

• New materials with different crystal structures have expanded the capabilities of LEDs.Jupiterimages/Photos.com/Getty Images
  
  The energy difference in a semiconductor is called the bandgap. The bandgap of a material depends upon what it's made of. Green LEDs of the 1970s and 1980s were made from gallium phosphide with some extra nitrogen atoms thrown in. Today, low power green LEDs are still made from gallium phosphide. The semiconductor at the heart of white LEDs is a combination of gallium indium nitride and gallium nitride, and its special feature is that it can put out lots of blue light. GaInN/GaN can also be used to make high-power green LEDs.
  
  

Structure

• White light can be produced by combining the light of three separate LED chips.Koichi Kamoshida/Getty Images News/Getty Images
  
  Green LEDs have a single chip with a single bandgap, therefore a single wavelength. All LEDs are single wavelength devices, so they have to use some sort of color mixing scheme to make white light. One design mixes the light from three different single color LEDs, usually red, green and blue. Another design has a layer of phosphor on top of an LED. A phosphor is a material that absorbs light at a short wavelength and emits light at a longer wavelength. In white LEDs, the short wavelength is from the semiconductor chip that emits blue light, and it joins with the yellows and reds from the phosphor to make white light.
  
  

Power

• The semiconductor crystal is just a thin layer of atoms. When electrical current runs through that thin layer, if there are defects causing regions of high electrical resistivity, then the crystal will heat up. When the crystal heats, the resistivity gets even higher, which makes the crystal heat even more --- causing it to burn up. The early gallium phosphide diodes couldn't handle more than about 20 milliamps of current before they burned up. As of 2011, high brightness diodes can take about 50 times as much current before they run into trouble. More current equals more light.