Replacing older technologies and being replaced by newer ones is the contest that is far away from reaching any solid conclusion. A mesmerizing example is the Liquid Crystal Display (LCD), an electronically modulated optical device that has returned the previously most commonly used LED displays. Though the primary focal point of our discussion is what is LCD, some gossip about technologies that have replaced it helps us broaden our knowledge about emerging displays and their limitations. This flat panel display uses light modulating properties instead of light emitting, as seen in its predecessors, like gas plasma displays and light emitting diodes.
On one end, an LED device is a light source and emits light as the primary form of operation. Conversely, the liquid crystal display modulates light by coupling liquid crystals with polarizers. The device achieves this modulation and produces images on the screen using a reflector or backlight. This backlight provides illumination from the rear or other sides of the panel instead of front lights and helps produce a more profound visual image. How well these panels have set their place in the technology town is evident from their pretentious features, such as low-key power utilization, much thinner and flat displays, and negligible heat emission.
These displays are featured in almost all devices like computer monitors, televisions, laptops, mobile screens, and tablets. The significant variations in appearance and performance of the panel compared to LED have made it a unique and valuable gadget. However, an OLED display is a new technology that has given tough challenges to the popularity of displays.
How LCDs Work
The nuclear characteristics of any display device are pixels and sub-pixels, which control the quality of the display and the colors it produces. Millions of pixels compose a display screen and hence, decide its quality. The greater the number of pixels, the better the image quality you obtain. Usually, their value is indicated in numbers and divided into three subpixels: named RGBs such as Red, Green, and Blue. These unique colors join to form multiple color combinations. From a bigger perspective, these colors from millions of pixels work together to produce many new colors. That is how pixels create colorful images on a display screen by readily switching on and off.
Each type of display, whether old or new, uses different means of controlling its pixels. They employ unique tactics to manage pixels and produce images. For example, when we explore the structural configuration of a liquid crystal display, we notice that two polarizers and liquid crystals use a backlight to brighten the screen. These pixels operate between two layers of polaroid glass filters, one placed in front and the other behind these pixels. Moreover, liquid crystals also lie in this region and rely on an electric field rather than an electric current.
But what is the working principle that an LCD implements to produce visual images? The liquid crystals require an electric field to flow; if there is no such field, these molecules twist at 90 degrees. Light pixels emitting from the backlight become polarized after passing through the first polarizer and twist when confronting the twisted liquid crystal molecules. This crooked stream of pixels is blocked when it reaches the second polarizer and turns the display black for viewers. On the other hand, with the application of an electric field, twisted crystal molecules untwist, and when the stream of light pixels flows through them, it goes straight without bending or twisting.
This straight light flux hits the second polarizer and passes through it, lights up the screen, and viewers can see the bright display with images. Using an electric field instead of an electric current solves the query of why an LCD consumes less power than an LED or other older displays. It comprises two types of matrix display grids, passive and active. The active matrix grid is far more intelligent than the passive one and is also named the Thin Film Transistor (TFT) display. Some of the leads it enjoys over the passive matrix include a high refresh rate, higher resolution, freedom to choose an angle, and high response time.
An active display deposits a thin film of transistors in its glass matrix, where one transistor holds the luminance of a pixel at each pixel transaction. These transistors do not need a higher current to control pixels and their brightness; therefore, they help improve the screen refresh time by holding more control over the current switching. Conversely, a passive matrix LCD recruits conductors positioned horizontally and vertically to create an intersection that controls a single pixel. The original technology employs single scanning, which means it scans the grid only once in a while; however, some passive displays are also eligible for double scanning the current stream.
Types of LCDs
LCDs are of different types, such as;
- Twisted Nematic Displays: Compared to other LCDs, this one delivers less color smearing and fast pixel response times. However, it lags in other areas, like poor color contrast ratios, limited viewing angles, and a color shift if the viewing angle is not set perpendicular to the display.
- IPS Panels: The In Panel Switching Displays are designed to improve the issues faced with the twisted nematic displays, which can broaden the viewing angle and enhance the quality of colors produced. For this, a layer of liquid crystals runs parallel or in-plane to the two glass surfaces with the power push from an electric field to create images.
- VA Panels: The Vertical Alignment panels showcase traits that stand between TN and IPS panels. For instance, they possess the best color contrast ratio but lag behind IPS panels regarding viewing angles. Similarly, compared to the TN displays, VAs show quite a slow response time but excel in producing colors as they can generate a full sRGB spectrum.
- AFFS Displays: Advanced Fringe Field Switching displays are superior to IPS panels in producing a wide range of colors. They are best known for their wide viewing angle and brilliant and authentic transmittance of colors.
LCD vs OLED vs QLED
Now LCDs are also being outplaced by more competent displays like organic light-emitting diodes (OLEDs). However, their use has not become obsolete and is still widely used. An OLED has significant distinctions like it uses just one glass panel instead of two and does not recruit a backlight to produce images. Each pixel lights up and glows individually to prevent light leakage, as in a liquid crystal display. That is why devices with this display have thinner packaging and deeper blacks. In this panel, when only a small area needs to be lit up, and the rest is supposed to be dark, the entire screen still appears bright behind an opaque panel.
This brightness happens because of the leakage of light on the front panel. Conversely, an OLED does not allow this leakage of resources and also gobbles less power. This technology allows users to bend and fold the gadget and use it with maximum flexibility. They boast this feature even in smartphones. These traits seem versatile, which adds to its overall cost but are still prone to burn-in and exhaustion. Another modern display type is QLED which stands for Quantum Light Emitting Diode. It can be considered a sub-type of liquid crystal display because of all the similarities with only one addition.
What makes QLED peculiar is the other quantum dot film layered over the LCD, which enhances colors and their brightness. The display type is manufactured by Samsung and is available in newer devices like digital cameras, smartphones, handheld gaming consoles, and flat displays. A comparison between OLED and QLED highlights the different features of each element. QLEDs have brighter displays, cover wide color gamuts, and protect their components from burn-in and easy degradation over time. On the other hand, OLEDs work without a backlight and have perfect blacks and better color contrasting aspects.
LCDs is the most prominent and dominant technology in the display market as it has overturned the wide usage of CRT monitors and plasma displays which rarely appear on users’ desk anymore. Its prominent advantages are that it is a thin casing, less consumption of power, and light modulation instead of emission. However, every technology confronts some limitations. The display depends on backlighting for its operationality and shows slow pixel response time and limited viewing angle. The latest displays, however, such as OLED and QLED, have better features than an LCD and tend to gloss over their limitations.