LED diode tutorial

LED Diode Definition – Construction, Characteristics and Applications

Light Emitting Diode


led diode definition

Light-emitting diode (LED, LED diode) – type of semiconductor diode, that also belongs to the category of optoelectronic components. Typical LED’s construction is based on “p-n semiconductor crystal junction” (more about “p-n junction” here)After LED has been polarized by positive electric voltage (forward-bias) that exceeds it’s threshold voltage value, it will start emiting electromagnetic radiation in the visible and infrared light spectrum.

led diode

Fig. 1. LED symbol

LED – Construction

Color and wavelength of light radiation emitted by LEDs are closely connected to the semiconductor material from which it was produced.  Usually, they are manufactured from compounds (bicomponents and multicomponents) of chemical elements from 3rd and 5th 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.

LED – Division based on the color of light radiation

ColorWavelenght λ [nm]
Ultraviolet (UV)< 380
Violet380 – 435
Blue435 – 500
Blue-Green500 – 520
Green520 -565
Yellow565 – 590
Orange590 – 625
Red625 – 700
Infrared (IR)> 700

Smooth change of wavelength is accompanied by analogous change in color. In the table above we’ve put ranges of  wavelength values in length-order to improve envision of the relation between wavelength and diode color.

LED – Current-voltage characteristics

The LED characteristics show that the color of the diode affects the power consumed by that LED. LEDs emitting infrared color consume the least amount of power, where white color consumes the most. This is because different diodes have different threshold voltages. You can see that on the LED characteristics shown below.

LED characteristics

Fig. 2. The group of the current-voltage LED characteristics showing differences in threshold voltages in different LED colors

LED – Principle of operation

The operating principle of Light-emitting diode is based on the electroluminescence phenomenon (producing electromagnetic radiation under the influence of the electric field). Electroluminescence occurs as a result of recombination (annihilation) pair of carriers (electrons and electron holes) 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.

Flexible LED displays

The dynamic development of electronics that we are witnessing today 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 used in TVs, mobile phones, smart watches or even in clothing.

flexible led

Fig. 3. Source: digitaltrends.com

Device, as a whole (electronic circuit and components) is incorporated into a paper-thin and even transparent foil. Rapid growth of OLED technology was also one of the reasons for further development and popularity growth of flexible electronics. Such solutions enable users to interact with such devices by twisting them, bending or folding across both planes. As a flexible display advantages we can consider e.g. cheaper manufacturing process, exploitation, which may translate into the final, cheaper price in the electronic stores in the future.

Examples of LED 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.

LED – Advantages

  • ability to choose light colors (wavelength),
  • low operating voltage (single LEDs need from 2 to 4V to start working),
  • low power consumption,
  • small sized component (compared to a standard bulb even very small),
  • high efficient,
  • low energy losses,
  • durable.

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