Light-emitting diode (LED, LED diode) – a type of semiconductor diode, also one of the optoelectronic components. The simplest LEDs are implemented as ordinary p-n semiconductor junctions. After LED diode polarity is forward-biased with enough voltage it starts emiting electromagnetic radiation in the visible and infrared light.
LED diode symbol
LED diode construction
Color and wavelength of radiation emitted by LEDs are closely connected with the semiconductor material from which it was made. Usually they are manufactured from compounds (bicomponents and multicomponents) of elements from III and V group of the Mendeleev’s Periodic Table (for example, GaAs – gallium arsenide, GaP – gallium phosphide, GaAsP – arseno-phosphide gallium with right-doping). Elemental composition of the diode is assorted in a way that semiconductor structure obtained in the process will allow the emission of light in the desired spectral range. “p-n junctions” of LEDs with GaAs are mostly produced with a diffusion technique. It ensures a high quantum efficiency. Group of interconnected diodes are used in various types of displays for example in seven-segment displays.
The division of LEDs based on the color of light radiation
|Color||Wavelenght λ [nm]|
|Ultraviolet (UV)||< 380|
|Violet||380 – 435|
|Blue||435 – 500|
|Blue-Green||500 – 520|
|Yellow||565 – 590|
|Orange||590 – 625|
|Red||625 – 700|
|Infrared (IR)||> 700|
Smooth change of wavelength is accompanied by analogous change in colour. In the table above we’ve put ranges of wavelength values in length-order to improve envision of the relation between wavelength and diode colour.
LED diode characteristics
The LED characteristics show that the color of the diode affects the power consumed by the LED. Starting from the infrared color ending in white color, the forward voltage of the LED increases. The LED characteristics prove the dependence of the conduction voltage on the wavelength. The wavelength of the UV color is <380, and the IR color >700.
Operating principle of LED diode
The principle of light-emitting diode operation is based on the electroluminescence phenomenon (producing light under the influence of the electric field). Electroluminescence occurs as a result of recombination (annihilation) pair of carriers (electrons and hole) in the area of the “p-n junction”. While electrons flow from higher to a lower energy-level, power dissipation occurs as a heat (non-radiative recombination – at semiconductors with n-oblique energy gap) or light (radiative recombination – semiconductors with a simple energy gap). During this flow, electron energy is converted into a quantum of electromagnetic radiation.
The dynamic development of electronics that we are witnessing would not be possible without simultaneous researches in interdisciplinary science called nanotechnology. We have reached such a point that we are not surprised by the flexible LED screens (OLED) used in TVs, mobile phones, smart watches or even in clothing.
Device as a whole (electronic circuit and components) is incorporated into a paper-thin and even transparent foil. This is possible thanks to OLED technology, which was the reason for further development and popularity growth of flexible electronics. Such solutions enable users to interact with the device by twisting it, bending or folding across both planes. Such screens are e.g. cheaper in production, exploitation that translates into the final, cheaper price in the stores.
Advantages of LED diode
- ability to choose light colors,
- low operating voltage (single LEDs need from 2 to 4V),
- low power consumption,
- small sized component (compared to a standard bulb even very small),
- high efficient,
- low energy losses,
Examples of LED diode varieties
- RGB LED (Red Green Blue LED) – has three colors in “one box”, which allows to generate any color,
- IR (Infrared) – it emits infrared radiation that is used for example in data transmission, also in older models of mobile phones (some of you may not remember this!),
- HB LED (High Brightness LED) – diodes with high brightness. They are used in automotive, traffic lights, streetlights or in frontal bicycle lights.