Liquid crystal molecules are very susceptible to the influence of external electric fields and generate induced charges. When a small amount of charge is added to the transparent electrode of each pixel or sub-pixel to generate an electrostatic field, the molecules of the liquid crystal will be induced by this electrostatic field to induce induced charges and generate electrostatic torque, which changes the original rotational arrangement of the liquid crystal molecules, thereby changing the rotation amplitude of the light passing through. Change a certain angle so that it can pass through the polarization filter.

Some LCDs turn black when they are exposed to alternating current, which destroys the spiral effect of the liquid crystal. When the current is turned off, the LCD becomes brighter or transparent. This type of LCD is commonly found on laptops and cheap LCDs. Another type of LCD commonly used on high-definition LCDs or large LCD TVs is that when the power is turned off, the LCD is opaque.

In 1888, Austrian chemist Friedrich Reinizer discovered liquid crystals and their special physical properties.

In December 1970, the twisted nematic field effect of liquid crystals was patented in Switzerland by Sint and Helfrich at the Central Laboratories Hoffmann-Le Roque. However, the year before, in 1969, James Ferguson had discovered the twisted nematic field effect of liquid crystals at Kent State University in Ohio, USA, and registered the same patent in the United States in February 1971. In 1971, his company (ILIXCO) produced the first LCD based on this property, which soon replaced the inferior DSM type LCD. It was not until 1985 that this discovery became commercially viable. In 1973, Japan's Sharp Corporation first used it to make digital displays for electronic calculators. In the 2010s, LCDs have become the main display devices for all computers.

Without voltage, light will move along the gap between liquid crystal molecules and turn 90 degrees, so light can pass through. But after voltage is added, light moves straight along the gap between liquid crystal molecules, so light is blocked by the filter.

Reflective LCDs, commonly found in electronic clocks and calculators, (sometimes) illuminate the screen by reflecting external light back from a diffuse reflective surface behind the LCD. This type of LCD has a higher contrast ratio because the light passes through the liquid crystal twice, so it is cut twice. Not using a lighting device significantly reduces power consumption, so battery-powered devices last longer. Because small reflective LCDs consume so little power that a photocell is enough to power them, they are often used in pocket calculators.

LCD technology also changes brightness based on the size of the voltage. The color displayed by each LCD sub-element depends on the color screening program. Since the liquid crystal itself has no color, color filters are used to produce various colors instead of sub-elements. Sub-element can only adjust the grayscale by controlling the intensity of light passing through. Only a few active matrix displays use analog signal control, and most use digital signal control technology. Most digitally controlled LCDs use eight-bit controllers, which can produce 256 levels of grayscale. Each sub-element can show 256 levels, so you can get 2563 colors, and each element can show 16,777,216 colors. Because the human eye does not feel the brightness linearly, and the human eye is more sensitive to low brightness changes, this 24-bit chromaticity cannot fully meet the ideal requirements. Engineers use pulse voltage regulation to make the color changes look more uniform.
In a color LCD, each pixel is divided into three units, or sub-pixels, and additional filters are marked red, green and blue respectively. The three sub-pixels can be controlled independently, resulting in thousands or even millions of colors for the corresponding pixel. Old CRTs use the same method to display colors. Depending on the need, the color components are arranged according to different pixel geometries.

A liquid crystal display commonly found in electronic watches and pocket computers that consists of a small number of segments, each with a single electrode contact. An external dedicated circuit provides charge to each control unit, which can be cumbersome with more display units (such as liquid crystal displays). Passive array liquid crystal displays for small monochrome displays, such as those on PDAs or older laptop screens, use super twisted nematic (STN) or double-layer super twisted nematic (DSTN) technology (DSTN corrects the color deviation problem of STN).

Current high-resolution color displays, such as computer monitors or televisions, are active arrays. Thin-film transistor liquid crystal displays are added to polarizers and color filters. Each pixel has its own transistor, allowing single pixel control. When a column line is turned on, all row lines are connected to a whole row of pixels, and each row line is driven with the correct voltage, the column line is turned off and the other row is turned on. In a complete picture update operation, all column lines are turned on in a time sequence. Active array displays of the same size will appear brighter and sharper than passive array displays, and have a short response time.

LCD panels are more likely to have defects than IC boards because of their larger size. For example, a {{0}}inch SVGA LCD has 8 bad pixels, while a 6-inch wafer has only 3 defects. However, 3 defects on a wafer that can be partitioned into 137 ICs is not very bad, but discarding the LCD panel means 0% output. Due to fierce competition among manufacturers, quality control standards have been raised. If an LCD has four or more bad pixels, it is easier to detect, so the customer can request a replacement. The location of the bad pixel in the LCD panel is also not negligible. Manufacturers often lower standards because the damaged pixels are in the center of the display. Some manufacturers provide a zero bad pixel guarantee.

Active matrix LCDs use less power than CRTs. In fact, they have become the standard display for portable devices, from PDAs to laptops. But LCD technology is still too inefficient: even if you turn the screen white, less than 10% of the light emitted from the background light source passes through the screen; the rest is absorbed. So new plasma displays now use less power than LCDs of the same area.

PDAs, such as Palm and CompaqiPAQ, often use reflective displays. This means that ambient light enters the display, passes through the polarized liquid crystal layer, hits the reflective layer, and then reflects back out to display the image. It is estimated that 84% of the light is absorbed in this process, so only one-sixth of the light is used, which, although there is still room for improvement, is enough to provide the contrast required for visible video. One-way reflection and reflective displays make it possible to use LCD displays with minimal energy consumption under different lighting conditions.

Zero-power display

In 2000, a zero-power display was developed that does not use electricity when in standby mode, but this technology is not currently available for mass production. Nemoptic, a French company, developed another zero-power thin-film LCD technology, which was mass-produced in Taiwan in July 2003. This technology is targeted at low-power mobile devices such as e-books and portable computers. Zero-power LCDs also compete with electronic paper.