How do LCD Displays Work?

Liquid-crystal display (LCD) is a popular type of technology used in electronic displays. As the name suggests, it’s characterized by the use of liquid-filled crystals to produce images. Because liquid crystals have light-modulating properties, LCDs are particularly effective for this purpose. The liquid crystals don’t necessarily produce the light used to create the images. Rather, they “propagate” light created by a separate device (backlight). To learn more about LCD displays and how they work, keep reading.

How do LCDs work?

Unlike CRT monitors, LCD monitors cannot illuminate themselves, and so they require a light source: the backlight. This backlight is most frequently made of the well-known LEDs which stand for light-emitting diodes. Sourced from the backlight, light is moved through the back polarizer and back substrate, into the liquid crystals. Now, the light waves can behave in a variety of ways. Backlight used in LCD displays can be LED (Light Emitting Diode) backlight or CCFL (Cold Cathode Fluorescent Lamp) backlight. LED backlights use less power which becomes more popular, while CCFL is lower cost for large size LCD displays such as large LCD TV. Recently, quantum dots technology is used to increase the LCD contrast.

Electrodes are the controlling factors of the liquid crystal behavior, and thus also the light behavior. By conducting or not conducting a current into the crystal layer, the light may or may not be able to pass through the liquid crystals in a manner that will allow passage through the polarizer. Because of this role, electrodes in LCDs are often made of indium tin oxide (ITO). ITO has good conducting properties and can also make for a transparent electrode which is essential to the appearance of displays today.

How the electrodes affect the liquid crystal alignment can vary depending on the method of alignment used (twisted nematic, multi-domain, in-plane switching). For example, twisted nematic liquid crystals are oriented in a twist when no electric field is present which then polarizes the light passing through the layer; when the electrodes apply the field in full, the twist will straighten out, no longer polarizing the light, and so no light passes. In each of these alignment types, the electrodes are placed differently within the structure, altering the properties of the display, such as width of viewing angle, power consumption, and response time. Despite these different alignment methods, the liquid crystal layer’s purpose remains the same: to polarize the light so that the polarized light passes through to the surface of the display. By polarizing the light transmitted from the backlight, the liquid crystal molecules play a role in how much of the light passes through the polarizing filters, whether it be all, none, or a partial amount.

For color displays, there is an additional step between the polarization and interaction with the polarizer. After polarization in the crystal layer, the light passes through an RGB (red green blue) color filter. LCD displays work by using individual pixels to display visuals, moving or stationary. Each pixel will display a color mixed by the RGB color filter with each color’s filter associated with one of the pixel’s sub-pixels. The sub-pixels are where the degree of light is determined, thus affecting the degree of prominence of its respective color. With the groups of sub-pixels combined under a pixel, the RGB colors will mix in a certain way to create a pixel color that will then work with other pixels to finally create the image seen on the display device.

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Encyclopedi Optoeletronics Technology Co., Ltd (EOTSZ), founded in 2009, is engaged in the R&D and manufacturing of optical display human-computer interaction products. It has a rich team of experts at home and abroad, with an average experience of about 11 years. It has a strict quality management system (ISO9001, TS16949 in progress), a number of industrial patents, and works on analog circuit software. If you are in need of LCD screens, kindly contact us today!