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Differences among LCD, LED and OLED

日期:2018-11-23   类型:Technical Information

Differences among LCD, OLED and QLED

Traditional TV display screens are mostly LCD screens. In recent years, with the development of new technologies, OLED screens have gradually come into people's view, but QLED has come out again before OLED has a firm foothold. So, what's the difference between the screens of these three technologies? Today, let's make a careful distinction.


1、LCD

LCD is the abbreviation of Liquid Crystal Display in English, which refers to liquid crystal display. The structure comprises a plastic ball, a glass ball, a frame glue, a glass substrate, an upper polarizer, a directional layer, a liquid crystal, a conductive ITO pattern, a conduction point, an IPO electrode and a lower polarizer.


LCD basic structure

TFT-LCD is a thin film transistor liquid crystal display. Its basic structure is to place a liquid crystal cell between two parallel glass substrates, set a thin film transistor (TFT) on the lower substrate glass, and set a color filter on the upper substrate glass. The rotation direction of the liquid crystal molecules is controlled by changing the signal and voltage on the thin film transistor, so as to control the emission of polarized light from each pixel to achieve the display purpose.


TFT structure

The principle of liquid crystal display is that liquid crystal will show different light characteristics under the action of different voltages. LCD is composed of many liquid crystals arranged in an array. In monochrome LCD, a liquid crystal is a pixel (the smallest unit that can be displayed on the computer screen), while in color LCD, each pixel is composed of three liquid crystals, red, green and blue. At the same time, it can be considered that there is an 8-bit register behind each LCD, and the value of the register determines the brightness of the three LCD cells. However, the value of the register does not directly drive the brightness of the three LCD cells, but is accessed through a "palette". It is unrealistic to equip each pixel with a physical register. In fact, it is only equipped with one row of registers. These registers are connected to each row of pixels in turn and loaded into the contents of the row. Drive all pixel rows once to display a complete picture.


LCD


2、LED

LED is the abbreviation of Light Emitting Diode. It is a kind of semiconductor diode, which can convert electric energy into light energy. When electrons and holes recombine, they can radiate visible light, so they can be used to make light emitting diodes. Like ordinary diodes, light emitting diodes are composed of a PN junction and also have single conductivity.


The principle is that when a forward voltage is applied to the light-emitting diode, the holes injected from the P area to the N area and the electrons injected from the N area to the P area recombine with the electrons in the N area and the holes in the P area within a few microns near the PN junction, respectively, to generate spontaneous emission fluorescence. The energy states of electrons and holes in different semiconductor materials are different. When electrons and holes recombine, the amount of energy released is different. The more energy released, the shorter the wavelength of light emitted. Diodes that emit red, green or yellow light are commonly used.


LED emitting light of different colors

LED, known as the fourth generation light source, has the characteristics of energy conservation, environmental protection, safety, long life, low power consumption, low heat, high brightness, waterproof, miniature, shockproof, easy dimming, beam concentration, simple maintenance, etc. It can be widely used in various fields such as indication, display, decoration, backlight, general lighting, etc. Such as LED display, traffic signal lights, automotive lights, LCD backlight, household lighting and other lighting sources.


Traffic light


3、OLED

OLED is the abbreviation of Organic Light Emitting Diode, and its Chinese name is Organic Light Emitting Diode. It is also called electromechanical laser display and organic light-emitting semiconductor. This diode was discovered in the laboratory by Chinese American professor Deng Qingyun in 1979.


The OLED is composed of an external OLED display unit and a luminescent material sandwiched therein, including a cathode, an emission layer, a conductive layer, an anode and a substrate. Each OLED display unit can generate three different colors of light under control.


OLED display technology has the characteristics of self illumination. It uses very thin organic material coating and glass substrate. When there is current, these organic materials will emit light. Moreover, OLED display screen has a large viewing angle and can save power consumption. Since 2003, this display technology has been applied to MP3 music players.


Nowadays, an outstanding representative of the use of OLED is the mobile phone screen. The OLED screen can display perfect picture contrast, and the display will be more vivid and realistic. LCD screen does not support bending due to the characteristics of liquid crystal. In contrast, OLED can be made into a bending screen.


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