As mentioned previously, Light-Emitting Diodes work along the same basic concept as traditional lighting sources – they generate light by electrical current flowing through them. This is where the similarities end however. Unlike traditional lighting sources which rely on heat or a chemical reaction in order to produce illumination, LEDs rely on a semiconductor for their light source. This is a unique technology that offers significant technological benefits and far greater potential for continuous advancement.
To explain how LEDs work, it is important to first understand what a semiconductor is and how it functions. Semiconductors are materials with varying ability to conduct electrical current. Light-emitting diodes are some of the simplest types of semiconductor in existence. Most semiconductors have impurities added to them in order to allow electrons to flow through, since on their own pure semiconductor material is a poor conductor. When a semiconductor has impurities added, this is referred to as doping.
Generally speaking, these semiconductors are made of aluminum-gallium-arsenide (AlGaAs). When this material is doped, it can either add free electrons or create holes in the material where electrons can go. When a semiconductor has extra electrons, it is known as an N-type material since it has extra negatively charged particles. When there are extra holes in the semiconductor, it is known as a P-type material since it effectively has extra positively charged particles.
The basic construction of a diode consists of a section of N-type and P-type material bonded together with electrodes on each end. In this arrangement, electricity is only conducted in a single direction. With no voltage applied, a depletion zone is created between the P and N type materials, restoring the semiconductor to its original insulating state where no electrons or electricity can flow.
In order for the depletion zone to be removed, electrons must be moved from the N-type area to the P-type area, as well as the holes in the reverse direction. Once this occurs through a significant enough voltage, the depletion zone is removed and the charge moves across the diode. It is this interaction between the electrons and holes that generates the light seen in an LED.
Specifically, the light generated by an LED is actually a result of the release of photons from the movement of these electrons from one orbital of an atom to another. The greater the distance between orbitals, the greater the energy released by an electron during the interaction and the higher the frequency of light produced. Inversely, the shorter the distance between orbitals, the lower the energy released during the interaction and the lower the frequency. Lower frequencies are often in the infrared portion of the light spectrum which means it is invisible to the human eye.
This variability in an electron’s orbital change is responsible for the wide range of color temperature options available in LED lighting today. Compared to traditional lighting with fixed or restricted color temperatures, LEDs offer a nearly endless range of possibilities for every type of bulb. In fact, certain LED fixtures offer the option for the user to easily switch between different color temperatures.
