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Liquid crystal display, also known as LCD, is a flat-panel display technology commonly used in televisions and computer monitors. It is also used in the screens of mobile devices, such as laptops, tablets and smartphones. LCD monitors not only look different from bulky CRT (cathode ray tube) monitors, but they also operate very differently. Instead of emitting electrons on a glass screen, an LCD has a backlight that provides a light source for individual pixels arranged in a rectangular grid.
How is a liquid crystal display constructed?

The LCD screen consists of a thin layer of liquid crystal material sandwiched between two electrodes on a glass substrate with two polarizers on each side. A polarizer is a type of light filter that lets light waves of a particular polarization pass through while blocking light waves of other polarizations. The electrodes need to be transparent, so the most popular material is ITO (indium tin oxide).

Since the LCD itself cannot emit light, the backlight is usually placed behind the LCD screen to be seen in a dark environment. The backlight can be an LED (light emitting diode) or CCFL (cold cathode fluorescent lamp). LED backlighting is the most popular. Of course, if you prefer to have a color display, a layer of color filters can be made into an LCD unit. The color filter consists of RGB colors. You can also add a touch panel to the front of the LCD.

How does an LCD work?

The first mass-produced LCD panel technology was called TN (Twisted nematic). The principle behind LCD is that when the liquid crystal molecules do not apply an electric field, the molecules are distorted 90 degrees in the LCD unit. When light from ambient light or backlight passes through the first polarizer, the light is polarized and distorted by the liquid crystal molecular layer. When it reached the second polarizer, it was blocked. The viewer sees the display as black.

When an electric field is applied to liquid crystal molecules, they are untwisted. When polarized light reaches the molecular layer of the liquid crystal, the light passes directly through without being distorted. When it reaches the second polarizer, it also passes through and the viewer sees that the display is bright. Because LCD technology uses an electric field instead of an electric current (through which electrons pass), power consumption is low.

Basic knowledge of liquid crystal display

The most basic LCDS described above are called passive matrix LCDS and can mainly be found in low-end or simple devices such as calculators, utility meters, early digital watches, alarm clocks, etc. Passive matrix LCDS have many limitations, such as narrow viewing angles, slow response, dim, but high power consumption.

To improve the shortcomings, scientists and engineers developed active matrix LCD technology. The most widely used is TFT (thin film transistor) LCD technology. Based on TFT LCD, more modern LCD technology has been developed. The most famous is IPS (flat switching) LCD. It has an ultra-wide viewing Angle, excellent image quality, fast response, high contrast, few aging defects and so on.

IPS LCD is widely used in LCD, LCD TV, iPhone, tablet computer and so on. Samsung even revolutionized the LED backlight, becoming a QLED (quantum dot) to turn off the LED where the light is not needed to produce a deeper black.