Light emitting diodes do exactly what their name implies; they emit light. But how? And why? If you’re interested in diving into the world of LED, answering these questions is a natural starting place. So let’s geek out for a bit by exploring the process of electroluminescence! (Don’t worry, we won’t get too technical.)
To explain how an LED works it might be easiest to first explain how a traditional incandescent bulb works. In an everyday incandescent lightbulb like the ones you’d screw into your ceiling or a lamp, light is created when electrical energy is passed through the bulb’s filament, which is a wire usually made of tungsten. As this energy passes through, the filament disperses the energy it receives in the form of heat and, as a byproduct, light. This process is called incandescence. Tungsten is used for these filaments because it has a high melting point relative to other metals, meaning it can accept –and thus disperse- more energy before breaking down. This rudimentary method for producing light was once revolutionary but now is understood to be incredibly inefficient because over 90% of the inputted energy is released as heat.
An LED works quite a bit differently. Unlike an incandescent bulb, which produces light as a byproduct of heat, an LED diode produces light through electroluminescence, the production of light in response to the running of an electrical current. Electroluminescence is what happens when negatively charged free electrons, excited by an electrical current, combine with positively charged “electron holes” within a semiconductor. Because the electron holes have a lower energy level than the electrons themselves, the electrons must release energy in order to combine.
This energy is released in the form of photons, or light waves. The length of these waves (and thus the color of their light) is determined by the size of the “energy band gap”’ of the semiconductor. This gap is the energy disparity the electrons must make up to transition from their starting place on the conduction band of the semiconductor to the electron holes on the valence band of the semiconductor. Basically, it is the bridge they must cross. As this bridge gets larger, the color of the resulting light will change from infrared, to red, to violet, and then to ultraviolet.
Now, just because these photons are released by the electrons does not mean they necessarily escape the semiconductor. Depending on the coating and shape of the semiconductor, these waves can either escape as light or refract inwards and be wasted as heat. This means that while LEDs are far more efficient than incandescent bulbs, not all LEDs are created equal, though the reasons why are a topic for another day. While we’re on the subject though, if you are indeed curious what makes one LED different than another, we’ve got a webinar that lays it all out for you!