LCDs

LCDs, or liquid-crystal displays, are flat-panel displays that control light with liquid crystals confined between two polarizers. The crystals do not emit light but change orientation in response to electric fields, altering light transmission through the polarizers. This enables the creation of images when combined with a backlight.

Modern LCDs use an active-matrix design, typically a thin-film transistor (TFT) array that individually address each pixel. A common stack includes glass substrates with transparent electrodes, alignment layers to set initial crystal orientation, a liquid-crystal layer, color filters for color displays, and a backlight. The backlight, most often LED-based in contemporary devices, provides illumination that passes through the front polarizer, the crystal layer, and the viewing polarizer.

Types and performance characteristics vary. Twisted-nematic (TN) displays are inexpensive and have fast response times, but typically show narrower viewing angles and lower color accuracy. In-plane-switching (IPS) displays offer wider viewing angles and better color reproduction, while vertical-alignment (VA) displays often deliver higher contrast. Other variations include advanced color and brightness management within each pixel.

The development of LCDs began in the 1960s and 1970s, with twisted-nematic cells becoming commercially important in the 1980s and 1990s. The shift to LED backlights and refined TFT matrices has driven improvements in brightness, energy efficiency, and color fidelity. LCDs are widely used in computer monitors, televisions, smartphones, displays in consumer electronics, and instrumentation.

Advantages include thin form factor, low power consumption, and good resolution capability. Limitations can include viewing-angle dependency, black level and contrast limitations compared with some alternatives, color and brightness uniformity challenges, and aging effects.