A light-emitting diode (LED short of English light-emitting diode, dt light-emitting diode, also luminescent diode) is a light-emitting semiconductor device whose electrical properties correspond to a diode. Electric current flows through the diode in the forward direction, it emits light, infrared radiation or ultraviolet radiation at a rate dependent on the semiconductor material and the doping wavelength.
- LEDs are diodes, in which electrons emit radiant energy as light.
- For the multi-color image reproduction units are of three diodes required (red, green, blue) to be able to reproduce the full color spectrum in the RGB color model.
- Three such diodes together form one pixel.
- The pixel pitch (also: pixel pitch) defines the physical resolution of a plant - the smaller the distance of the diodes, the higher the resolution.
- Virtual pixel incure by software-controlled simulating a fourth diode per pixel.
- SMD technology combines three diodes together on a board and so achieves a higher resolution.
- The resolution is related to the viewing distance: the smaller the pixel pitch, the closer the viewer on the LED module can be located and still see a good picture. (For a pixel pitch of 20 mm, the minimum viewing distance is about 20m.)
- The color depth (bits) indicates the number of possible levels of brightness per pixel. For example, 8 bits = 256 levels per diode = 16.8 million tones per pixel.
- The processing power of an LED system affects the clock frequency in which they can generate countless frames that interprets as a moving image. The frame rate we measured in Hertz or Mega Hertz (Hz/MHz).
- The luminance of LED displays is usually given in the unit Nit or lumen. Typical for outdoor video screens at events include well 5,000 Nit or lumen.
A liquid crystal display (LCD) or a liquid crystal display is a display or a screen whose function is based on liquid crystals that influence the direction of polarization of light when a certain level is applied to an electric voltage.
LCDs consist of segments that can change its transparency independently. To the orientation of the liquid crystals is controlled by an electric voltage to each segment. Thus, the permeability of polarized light which is generated by a backlight and polarizing filters changes.
If a display can display any type of content, the segments are arranged in a uniform grid (see pixels). For devices that are intended to represent only certain characters, the segments often have a specially adapted form, especially in the seven-segment display for representation of numbers (see also matrix display).
A further development is the active matrix display that includes for driving a matrix of thin film transistors (engl. thin film transistor TFT). In flat panel technologies, this technique dominated since about 2005.
In advertising, there is often talk of LED televisions since about 2009. This is in most cases also to liquid crystal displays (LCDs) for image representation, which are used for backlight LEDs (LED backlight). Screens with organic light emitting diodes (OLEDs) are not yet generally available for large televisions.
LCDs are used in many electronic devices, such as in consumer electronics of measurement devices, mobile phones, digital watches and calculators. Also, head-up displays and video projectors work with this technique.