Liquid-crystal display

Screens use light to show us pictures.

These screens use special tiny bits. These bits are called liquid crystals. They do not make their own light. Instead, they use a light behind them.

The crystals act like tiny doors. They let light through or block it. This makes colors and shapes. You see these screens on phones and watches. They are also on big TVs.

They are very helpful tools for seeing things.

A liquid-crystal display, or LCD, is a flat screen.

These screens do not make their own light. Instead, they use a backlight to shine light through them.

Inside the screen are tiny bits called liquid crystals. These crystals act like small shutters for light. They sit between two polarizers. A polarizer is a filter that only lets light pass in one direction. Without the crystals, the two filters would block all the light.

When we use electricity, we can change the crystals. This is called an electric field. In some screens, the crystals are twisted like a spiral. This twist lets light pass through. When we turn on the power, the crystals untwist. This blocks the light so the pixel looks black. By using different amounts of power, we can make many shades of gray.

Most color screens use red, green, and blue filters. These filters make the colors we see. LCDs are in many things. You can find them in watches, phones, and TVs.

A liquid-crystal display, or LCD, is a flat screen used to show information.

These screens are everywhere in our world today. You might see them on a large television or a computer monitor. They are also in small things like digital cameras, watches, and smartphones.

For a long time, people used heavy and bulky cathode-ray tube displays. Since the late 2000s, LCDs have mostly replaced those older screens. They are better because they use less energy to work.

LCDs do not make their own light. Instead, they use a backlight or a reflector to shine light through them.

Inside the screen, tiny molecules called liquid crystals sit between two polarizers. A polarizer is a filter that only lets light pass in one specific direction. If you put two polarizers together in a crossed way, they block all light. However, liquid crystals can change how light moves. In a twisted nematic device, the molecules form a spiral or helical structure. This twist rotates the light so it can pass through the second filter.

We can control these crystals using electricity. When an electric field is applied, the molecules untwist. This stops the light from rotating, so the second filter blocks it. This makes the pixel look black. By changing the amount of voltage, we can let different amounts of light through. This creates different levels of gray.

Most color screens use red, green, and blue subpixels to make images. These colors are made using special filters.

Scientists have studied liquid crystals for a long time. In 1888, Friedrich Reinitzer discovered them in cholesterol from carrots. Later, in 1927, Vsevolod Frederiks found a way to switch them with electricity. This was a very important step for all LCD technology. In the 1960s, George H. Heilmeier worked at RCA laboratories. He is credited with inventing the first working LCD. He used something called the dynamic scattering mode to make a display.

Making these screens is a very precise job. Manufacturers use a process called photolithography to make color filters on glass sheets. They use tiny particles of pigment that are only 40 nanometers across.

They also use a black grid called a black matrix. This grid keeps the colors from leaking into each other. In the past, this grid was made of Chromium. Now, makers use carbon pigment because it is better for the environment. This careful work allows us to see clear pictures on our devices every day.

A liquid-crystal display, or LCD, is an electronically modulated optical device. It is a type of flat-panel display used to show information.

LCDs do not emit light directly like a lightbulb does. Instead, they use a backlight or a reflector to produce images. These images can be in color or monochrome.

LCDs are used in many different ways. You can find them in large television sets and computer monitors. They are also in aircraft cockpit displays and instrument panels. Small screens are used in digital cameras, watches, calculators, and smartphones.

The mechanism of an LCD relies on the light-modulating properties of liquid crystals. A typical pixel consists of a layer of molecules between two transparent electrodes. These electrodes are often made of indium tin oxide (ITO). The layer is sandwiched between two polarizing filters. These filters are placed in a crossed arrangement, meaning their axes of transmission are perpendicular.

Without liquid crystals, light passing through the first filter would be blocked by the second. In a twisted nematic (TN) device, the molecules form a helical or twisted structure. This twist rotates the polarization of the incoming light. This rotation allows the light to pass through the second filter, making the device appear gray.

Electricity is used to control how much light passes through each pixel. When a voltage is applied, the liquid crystal molecules in the center untwist. This means the light is no longer rotated as it passes through the layer. The light remains polarized perpendicular to the second filter. Because the filters are crossed, the light is blocked and the pixel appears black. By varying the voltage, engineers can control the amount of light that passes through. This allows the display to show different levels of gray.

Most modern color LCD systems use subpixels to create images. These subpixels use color filters to produce red, green, and blue light. The manufacturing process involves photolithography on large glass sheets. These sheets are later glued to other glass sheets containing a thin-film transistor (TFT) array.

A black matrix is used to separate the red, green, and blue subpixels. This grid prevents light from leaking from one subpixel to another. This increases the contrast ratio of the screen. In the 1980s and 1990s, these matrices were made of Chromium. Today, manufacturers use a black colored photoresist with carbon pigment for environmental reasons. The pigments used in these resists have particles only 40 nanometers across.

There are different types of LCD technologies used for different needs. Twisted nematic (TN) displays are common for devices with low information content. However, many smartphones now use In-Plane Switching (IPS) LCDs instead.

For high-resolution displays like televisions, a matrix of pixels is used. This is often done using an active-matrix structure. Some older or simpler devices used a super-twisted nematic LCD. These were often limited to only three colors: orange, green, and blue.

The history of liquid crystals began with scientific discoveries in the late 19th century. In 1888, Friedrich Reinitzer discovered the liquid crystalline nature of cholesterol. In 1927, Vsevolod Frederiks described the Fréedericksz transition. This is the essential effect that allows liquid crystals to be switched by electricity.

In the 1960s, George H. Heilmeier at RCA laboratories achieved the first operational LCD. He used a method called the dynamic scattering mode (DSM). In this mode, applying voltage turns a clear liquid crystal layer into a milky, turbid state. Heilmeier is credited with the invention of the LCD.

LCD technology has significantly changed how we view digital information. Since the late 2000s and early 2010s, LCDs have replaced cathode-ray tube (CRT) displays. CRTs were heavy, bulky, and used more energy. LCDs are much more energy-efficient. Unlike CRTs, LCDs are not subject to screen burn-in. However, they can still experience image persistence. This is a known characteristic of the technology.