Although the technology for liquid crystal displays has been around since the 1970s — it was typically found in watches, clocks, and home appliances — widespread use of the technology didn't occur until the 1990s. During this time, the primary use of LCD technology was found in laptops due to the display's lower power consumption, smaller size, and lighter weight. As LCD technology improved, LCD screens soon became more popular in desktop monitors and televisions. In 2007, LCD televisions eclipsed sales of CRT-based televisions for the first time worldwide.
A basic LCD display consists of essentially three main parts: a layer of liquid crystal solution, polarizing panels, and a light source. The crystals themselves do not produce light. In a thin-film transistor liquid crystal display (TFT LCD), one of the most popular designs, the display consists of a liquid crystal solution, a color filter, and a glass substrate grid — all sandwiched between two polarizing filter panels.
Liquid crystals are rod-shaped polymers that bend in response to electrical currents. The liquid crystals act as millions of shutters, arranged in a grid formation to let a specific amount of white light to pass. This grid formation is created with microscopic grooves on a supportive glass substrate. In addition, thin-filmed transistors (TFT) serve as tiny capacitors that rapidly switch the LCD's pixels on and off. Each shutter pairs with a color filter to remove all colors except blue, green, or red; specific currents form colors from the primary color sub-pixels.
Set at right angles — horizontal and vertical — the polarizing panels are located on the rear and front of the liquid crystal shutters. Natural light cannot enter through both polarizing panels when set up in this manner, so light that travels through the rear polarizing panel must follow the liquid crystal's direction to exit through the front polarizing panel. The liquid crystals allow or block this light in response to specific currents to create the image.
LED stands for "light-emitting diodes." Acronyms aside, LED devices are actually LCD devices with the same basic design. Cold cathode fluorescent lamps, historically used as the backlight, must light the entire screen evenly on basic LCD devices. There is no way to vary the lighting intensity. LCD devices that use LED backlights can use local dimming, which creates better contrast and a more vivid display while consuming less energy. LED devices are typically available in two varieties: edge-lit and full-array. As the names suggests, an edge-lit LED features backlights around the edges while a full-array LED envelops the entire backlighting. Due to LED backlighting's versatility and lighter weight, most LCD smartphones and tablet displays also use LED lights.
Until the early 2000s, plasma displays were the most popular choice for large flat-panel, high-definition televisions. In simple terms, the idea of a plasma display is comparable to illuminating millions of tiny fluorescent lights. Plasma displays feature xenon, neon, and low levels of mercury gas contained in millions of tiny pixel cells that are sandwiched between two layers of glass. When high voltages of electricity are applied to the cells, the gases convert into a plasma state and create photons of ultraviolet light.
Although the eye cannot see ultraviolet (UV) light, each pixel cell is coated with phosphor, converting the UV light into visible light. Each pixel includes red, green, and blue phosphor sub-pixels that react to varying intensities of charges and blend to create the appropriate colors. Since each pixel is individually lit, the displays are bright and vivid and provide wide-angle viewing.
To ionize, or charge, the individual cells, plasma displays feature two types of electrodes also set between the glass plates. Address electrodes, found behind the plasma cells, are set vertically while transparent display electrodes run horizontally behind the front glass panel. A dielectric material and magnesium oxide layer protect the front display electrodes.
Together, the electrodes form a basic grid. As information relays from the display's microprocessor, the electrodes charge and send a current to the cells at the corresponding electrode intersection on the grid. The charge excites the gases in the cells, which then release the photons onto the phosphor sub-pixels.
By and large, plasma displays have not been introduced to computer monitors, tablets, or phones. Simply put, plasma displays are generally too large. Due to their design, scaling down plasma screens has proven to be a challenge.
Unlike other types of displays, which typically use inorganic compounds to create and emit light, organic light-emitting diodes (OLED) displays use the principle of electroluminescence in organic material to display images. A basic OLED display consists of a layer (or layers) of organic material set between two electrodes: the anode and the cathode. The most popular OLED design features two layers of organic material, which are known as the "emissive layer" and the "conductive layer." The organic layers — composed of organic molecules or polymers — and the two electrodes are all supported by a glass or plastic substrate.
Much like the polarizing panels of an LCD display, electrical currents similarly flow from the back anode electrode to the front cathode electrode. Instead of light flowing from a backlight — to be directed by liquid crystals — only electrical currents run through the organic layers. As the name suggests, light-emitting diodes provide their own illumination. As the current runs through the organic layers, electrons are given to the emissive layer by the cathode while electrons are removed from the conductive layer by the anode. The removal of electrons creates electron "holes" in the conductive layer.
At the boundary between the emissive layer and conductive layer, electrons jump into these electron "holes" of the conductive layer. In other words, electrons degrade to the energy of an atom missing an electron. As this happens, the electron releases its extra energy in the form of light photons. This process is how OLED displays emit their own light. Since the displays do not rely on a light source, OLED displays are thought to offer the best color contrast and deepest blacks. Instead of the red, blue, and green sub-pixels of other displays, thousands of primary-colored molecules are packed inside each pixel, offering superior color rendering.
Tablet and smartphone displays, in particular, have the most to benefit from OLED displays. OLED displays do not require a backlight, which reduces energy consumption and size. OLED displays can also be supported by a flexible plastic substrate, offering both flexibility and strength to significantly reduce the likelihood of damaged screens. OLED displays are also continually being improved, and some are flexible and lightweight enough to sew into clothing.
Before the introduction of large screen plasma and LED TVs, large panel projection screens were the pinnacle of home entertainment luxury. Unlike a projector and separate screen that you'd find at a movie theater, rear-projection systems resemble that of a traditional television as the projector is self-contained within the TV. In simple terms, a small detailed image is created and reflected or transmitted through a magnifying lens that casts the image onto a larger screen. For projector television display applications, the rest of the process has historically been through a CRT or LCD design.
Much like other types of displays, projection displays have also evolved, and the DLP projector is the latest step in its evolution. At the heart of the DLP projector's advanced design is the microchip semiconductor, known as the Digital Micromirror Device (DMD) chip. Featuring up to eight million hinged microscopic mirrors, the DMD chip coordinates with digital information, a light source, and a lens to project a highly detailed digital image onto a screen. To accomplish this, the DMD chip relies on coordinating microscopic hinges controlled by Digital Light Processing (DLP) technology.
First, the DLP technology adjusts the digital data to control brightness, screen size, and sharpness. Once the digital information adjusts, the information relays to the mirrors. The DMD's mirrors are like an incredibly advanced light switch, tilting either toward the light source (on) or away from the light source (off). Each mirror can do this up to 5,000 times a second. This forms a very detailed gray-scale to form the image. Before the light hits the mirrors, however, white light from the light source passes through a spinning color wheel that's synchronized with the DMD chip to create colored images.
Although the DLP projector uses the same basic design of older projectors — an image-creating device, mirrored lenses, and screen — these elements are now far more sophisticated. Many modern DLP projection models are replacing the traditional backlight projection with LED lights, which also eliminates the need for the color wheel.
In-home 3D displays have grown in popularity in recent years. Unlike other displays, the three-dimensional display produces image depth. There are essentially three types of 3D displays: passive, active, and autostereoscopic. The last is commonly known as a glasses-free 3D display.
The basic technology behind a passive 3D display is providing two slightly different images for each eye within each frame. One of these images is polarized horizontal while one is polarized vertically. When a viewer wears polarized glasses, these images enter through the corresponding polarized lens, combining the two images and providing the illusion of three dimensions.
Active 3D displays are a bit more sophisticated and require powered LCD glasses. Instead of displaying two images at once, like passive 3D displays, active 3D displays quickly flash one image for the left eye and one for the right eye. The 3D LCD lenses communicate with the TV, which synchronizes the LCD-filmed lenses to shutter from transparency to dark. This allows each eye to only see the frame that it's supposed to. The transparent versus opaque shutter occurs too quickly for the viewer to notice any type of flicker.
Autostereoscopic, or glasses-free, 3D displays are not widely available, but they are thought to be the future. Instead of relying on glasses to coordinate left eye and right eye perception, the screen itself provides the three-dimensional illusion. Using a technology known as the parallax barrier, the screen features tiny slits that only allow one separate image to each eye, providing a 3D effect when perceived together. However, the technology relies on a precise viewer-angle to work, one of the reasons for its limited availability.
One of the latest and most advanced options in screen technology is the 4K display. With 4,000 horizontal pixels, these displays essentially quadruple the pixel count found in typical high-definition displays. As a result, 4K displays are labeled as ultra-high-definition (often abbreviated as Ultra HD or UHD).
Due to the high number of pixels in a 4K display, these screens project incredibly sharp images. Users can expect more vivid colors, finer details and seamless pictures even on larger screens. In fact, the visible difference between 4K and 1080p (HD) displays is the most noticeable on 50-inch or larger screens. In addition, users will be able to sit closer to the screen without seeing individual pixels when watching on a 4K display. A number of manufacturers are combining 4K displays with curved screens, which further adds to the immersive viewing experience. Curved screens, including flexible OLED screens, offer better contrast quality, improved sharpness at the edges of images and complex depth that feels closer to 3D.
Similar to the transition to filming in HD, an increasing number of films and television shows are now being filmed in 4K. Notably, Amazon and Netflix have started streaming some 4K content already. Meanwhile, 4K movies are already commonplace in commercial movie theaters. The significant amount of content already being produced for 4K screens ensures that this technology is likely to become mainstream in the coming years.
Because 4K content is just starting to become widely available, televisions with this type of display include upscaling technology that converts SD and HD content to Ultra HD resolution. With good upscaling technology, converted content appears nearly as impressive as native 4K content.
In many instances, starting with widespread LCD usage, phone and tablet displays have evolved alongside other types of displays, such as TV screens and computer monitors. The processes are the same. Just like a TV screen, an LCD phone or tablet display relies on an electrical current, polarized liquid crystals, and colored sub-pixels to form an image. Because of the smaller size and lower power consumption, LED backlighting is most commonly used. In addition, the transition from hard glass panes to advanced aluminosilicate glass has made most modern smartphones and tablets much more resistant to breaking.
One of the unique properties of smartphone and tablet displays is the touchscreen. Along with the display's specific LCD or OLED design, circuitry and sensors are woven into the display to monitor changes to the display's particular electrical state. The changes in its electrical state are how the screen senses touch. There are two ways for a touchscreen to do this — one is known as "capacitive," and the other is known as "restrictive." A capacitive touchscreen features a layer of material that always holds an electrical charge. By touching the screen, the current changes, and the appropriate action is taken. Resistive touchscreens feature two layers of circuitry, conductive and resistant, and the pressure from your finger causes the circuitry layers to touch each other, resulting in a change of its electrical state.
Many tablets and smartphones are transitioning from LCD to OLED screens because an OLED screen is thinner. In addition, OLED's lack of backlight reduces power consumption. As stated before, OLED displays can also be supported by either a glass or flexible plastic substrate. For this reason, the next generations of tablets and smartphones are trending toward exploring the potential of flexible OLED displays.
Although a flexible OLED screen introduces much potential, other issues in engineering are preventing it from being realized. Many industry leaders are currently researching concepts, such as flexible batteries, to accommodate the next evolution of phones and tablets that could be made possible with flexible OLED displays.
This instance of the display's evolution pushing the need for new technological innovations has occurred repeatedly ever since the electromechanical television in 1884. As new display technology continues to evolve, it doesn't only increase the resolution of a device's screen — it also vividly displays human imagination. Subsequently, the evolution of display technology reflects our innovative past while offering a crystal-clear view of human potential for future achievements.