What are the differences between screens such as LCD, LED, OLED, AMOLED displays and more

We take you through the different types of electronic screens found in phones, tablets, monitors and televisions

This blog takes a close look at some of the leading electronic visual displays such as LCD, LED, OLED and AMOLED and their key differences...

What are the differences between screens such as OLED, LCD, AMOLED, LED displays.

Aug 28, 2019    By Team YoungWonks *

What are the key differences between leading electronic visual displays available in the market? Such are the times that we live in that today most of us cannot possibly imagine a life without an electronic device. In fact, we have managed to surround ourselves and depend on a growing number of electronic appliances. Several of these devices - as it happens - also have an electronic visual display; be it a mobile phone, a tablet, a desktop monitor or the television set. Without a doubt, these electronic screen devices have revolutionised the way we lead our lives now as all of the four devices have become increasingly commonplace to the point of becoming basic necessities. Which brings to our blog topic: what exactly is an electronic screen and which are the leading screen technologies available today? Read on to know more…

What is an electronic screen?

An electronic screen or an electronic visual display, informally called a screen, is basically a device used to display / present images, text, or video transmitted electronically, without creating a permanent record. As mentioned earlier, electronic visual displays include television sets, computer monitors, and digital signage in information appliances. As per the definition, an overhead projector (along with screen onto which the text, images, or video is projected) can also be called an electronic visual display. 

Different Screen Technologies in Use Today

Now we shall take a look at some of the leading electronic visual display technologies today. 

1. Cathode Ray Tube (CRT) display: A vacuum tube containing one or more electron guns and a phosphorescent screen, the cathode-ray tube (CRT) is used to display images. It modulates, accelerates, and deflects electron beams onto the screen to make the images. The images could be electrical waveforms (oscilloscope), pictures (television, computer monitor) or radar targets. CRTs have also been used as memory devices, wherein the visible light from the fluorescent material (if any) does not really have any significant meaning to a visual observer, but the visible pattern on the tube face could cryptically represent the stored data. In television sets and computer monitors, the front area of the tube is scanned systematically and repetitively in a pattern called a raster. Thanks to the intensity of each of the three electron beams - one for each additive primary color (red, green, and blue) - being controlled with a video signal as a reference, an image is produced. In modern CRT monitors and TVs, magnetic deflection bends the beams; magnetic deflection is essentially a varying magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although electrostatic deflection is often used in oscilloscopes, a type of electronic test instrument. CRT is one of the older screen/ display technologies. 

2. Flat-Panel display: Flat-panel displays are electronic viewing technologies that are used to allow people to see content (still images, moving images, text, or other visual material) in a range of entertainment, consumer electronics, personal computer, and mobile devices, and several kinds of medical, transportation and industrial equipment. They are much lighter and thinner than traditional cathode ray tube (CRT) television sets and video displays and are typically less than 10 centimetres (3.9 in) thick. Flat-panel displays can be classified under two display device categories: volatile and static. Volatile displays need pixels to be periodically electronically refreshed to retain their state (say, liquid-crystal displays). A volatile display only shows an image when it has battery or AC mains power. Static flat-panel displays rely on materials whose color states are bistable (say, e-book reader tablets from Sony), and they retain the text or images on the screen even when the power is off. In recent times, flat-panel displays have almost completely replaced old CRT displays. Most flat-panel displays from the 2010s use LCD and/or LED technologies. Majority of the LCD screens are back-lit as color filters are used to display colors. Being thin and lightweight, flat-panel displays offer better linearity and have higher resolution than the average consumer-grade TV from the earlier decades. The highest resolution for consumer-grade CRT TVs was 1080i, whereas many flat-panels can display 1080p or even 4K resolution.

3. Plasma (P) display: A plasma display panel (PDP) is a type of flat panel display that uses small cells containing plasma; ionized gas that responds to electric fields. Earlier, plasma displays were commonly used in larger televisions (30 inches and larger). But since more than a decade now, they have lost almost all market share due to competition from low-cost LCDs and more expensive but high-contrast OLED flat-panel displays. Companies stopped manufacturing plasma displays for the United States retail market in 2014, and for the Chinese market in 2016.

4. Electroluminescent display (ELD): Electroluminescent Displays (ELDs) are screens that make use of electroluminescence.  Electroluminescence (EL) is an optical and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field. 

So ELD then is a kind of flat panel display produced by sandwiching a layer of electroluminescent material between two layers of conductors. When the current flows, the layer of material emits radiation in the form of visible light. Basically, electroluminescence works by exciting atoms by passing an electric current through them, leading them to emit photons. By varying the material being excited, the color of the light being emitted is changed. The actual ELD is built using flat, opaque electrode strips running parallel to each other, covered by a layer of electroluminescent material, followed by another layer of electrodes, running perpendicular to the bottom layer. This top layer has to be transparent so as to allow light to escape. At each intersection, the material lights, creating a pixel.

5. Liquid Crystal Display (LCD): A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that makes use of the light-modulating properties of liquid crystals. Liquid crystals do not give out light directly; they use a backlight or reflector to create images in color or monochrome. LCDs display arbitrary images like in a general-purpose computer display or fixed images with low information content, that can be displayed or hidden, such as preset words, digits, and seven-segment displays, like in a digital clock. They use the same core technology, apart from the fact that arbitrary images are made up of a large number of small pixels, while other displays have larger elements. LCDs could be on (positive) or off (negative), as per the polarizer arrangement. For instance, a character positive LCD with a backlight has black lettering on a background the same color as the backlight, and a character negative LCD has a black background with the letters matching the backlight color. Blue LCDs typically get their characteristic appearance from optical filters being added to white. 

LCD screens are being used in several applications such as LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are seen in portable consumer devices such as digital cameras, watches, calculators and mobile telephones, including smartphones. LCDs are also found in consumer electronics products such as DVD players, video game devices and clocks. It is interesting to note that these displays are available in a wide range of screen sizes as compared to CRT and plasma displays. Also, while LCD screens have replaced heavy, bulky cathode ray tube (CRT) displays in almost all applications, they are slowly being replaced by OLEDs, which can be easily made into different shapes, and boast other advantages such as having a lower response time, wider color gamut, virtually infinite color contrast and viewing angles, lower weight for a given display size and a slimmer profile and potentially lower power consumption. OLEDs, however, are more expensive for a given display size and they can suffer from screen burn-in when a static image is displayed on a screen for a long time (for instance, the table frame for an airline flight schedule on an indoor sign), not to mention that there is currently no way to recycle OLED displays. LCD panels, on the other hand,  are susceptible to image persistence but they rarely suffer image burn-in as they do not use phosphors, plus they can be recycled, although this technology is not exactly common as yet. Not surprisingly, attempts have been made to increase the lifespan of LCDs in the form of quantum dot displays, which provide performance to that of an OLED display, but the Quantum dot sheet that gives these displays their characteristics can not yet be recycled. LCDs are also more energy-efficient and can be disposed of more safely than a CRT display. 

6. Light-Emitting Diode (LED) display: An LED display is a flat panel display that uses an array of light-emitting diodes as pixels for a video display. Their brightness lets them be used outdoors where they are visible in the sun for store signs and billboards. It was in 1962 that LED diodes first came into being; this was when the first practical LED was invented by General Electric’s Nick Holonyak Jr. This was also when they were mainly red in color. While the early models had a monochromatic design, the efficient Blue LED completing the color triad became available in the market only in the late 1980s. Today, large displays use high-brightness diodes to generate a wide spectrum of colors. In fact, recently, LEDs have also become a popular choice among destination signs on public transport vehicles and variable-message signs on highways. LED displays can offer general illumination in addition to visual display, as when used for stage lighting or other decorative (as opposed to informational) purposes. Several big corporations such as Apple, Samsung and LG are currently looking to develop MicroLED displays. These displays are easily scalable, and help with making the production process more streamlined. That said, production costs continue to be quite high and thus remain a limiting factor. 

7. Organic Light-Emitting Diode OLED display: An organic light-emitting diode (OLED), also called an organic EL (organic electroluminescent) diode, is a light-emitting diode (LED), where the emissive electroluminescent layer is a film of organic compound that gives out light in response to an electric current. The organic layer is located between two electrodes, at least one of which is transparent. OLEDs are used to build digital displays in devices such as television screens, computer monitors, portable systems such as smartphones, handheld game consoles and digital assistants. Typically, an OLED display works without a backlight because it emits visible light. This means that it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions, say in a dark room, an OLED screen can achieve a higher contrast ratio than an LCD, irrespective of whether the LCD uses an LED backlight or cold cathode fluorescent lamps. 

Also important to note an OLED display can be driven with a passive-matrix (PMOLED) or active-matrix (AMOLED) control scheme. In the former, each row (and line) in the display is controlled sequentially, one by one, as opposed to in the AMOLED where a thin-film transistor backplane is used to directly control and switch each individual pixel on or off, thus offering higher resolution and larger display sizes. 

Lastly, there are two main families of OLED: those based on small molecules and those making use of polymers. A big area of research is the development of white OLED devices for use in solid-state lighting applications. 

8. Active-Matrix Organic Light-Emitting Diode (AMOLED) display: AMOLED (Active-Matrix Organic Light-Emitting Diode) is a display device technology being used in smartwatches, mobile devices, laptops, televisions, media players and digital cameras. As mentioned earlier, it is a type of OLED; rather a specific type of thin-film-display technology where organic compounds form the electroluminescent material. What distinguishes it from PMOLED is the active matrix technology behind the addressing of pixels. An AMOLED display basically comprises an active matrix of OLED pixels generating light (luminescence) upon electrical activation that have been positioned or integrated onto a thin-film transistor (TFT) array, which in turn operates as a series of switches to control the current flowing to each individual pixel. AMOLED technology has continued to work towards consuming low power, becoming low-cost and offering scalability (mainly by offering larger sizes. 

9. Super AMOLED display: Super AMOLED is essentially an AMOLED display but it is a term coined for marketing purposes by leading device manufacturers. It is used to denote AMOLED displays that come with an integrated digitizer, i.e. the layer that detects touch is integrated into the screen, instead of overlaid on top of it. The display technology however is not an improvement on the AMOLED. For instance, Samsung claims that Super AMOLED displays reflect one-fifth as much sunlight as the first generation AMOLED. In fact, Super AMOLED displays that are part of the Pentile matrix family, are also at times known as SAMOLED. Other variations of this term include Super AMOLED Advanced, Super AMOLED Plus, HD Super AMOLED, HD Super AMOLED Plus and Full HD Super AMOLED. 

10. Quantum Dot (QD) display: A quantum dot display is a display device that uses quantum dots (QD), basically semiconductor nanocrystals that can generate pure monochromatic red, green, and blue light. Photo-emissive quantum dot particles are used in a QD layer which converts the backlight to give out pure basic colors that in turn enhance display brightness and color gamut by decreasing light loss and color crosstalk in RGB color filters. This technology is used in LED-backlit LCDs, though it applies to other display technologies as well (such as white or blue/UV OLED). 

Among devices employing QD screens, one can find electro-emissive or electroluminescent quantum dot displays, which are currently an experimental type of display based on quantum-dot light-emitting diodes (QD-LED). These displays are similar to active-matrix organic light-emitting diode (AMOLED) and MicroLED displays, as in light is produced directly in each pixel by applying an electric current to inorganic nano-particles. QD-LED displays are supposed to support large, flexible displays and not degrade as readily as OLEDs, making them good bets for flat-panel TV screens, digital cameras, mobile phones and handheld game consoles. As of 2018, all commercial products like LCD TVs that use quantum dots and are called QLED, use photo-emissive particles, whereas electro-emissive QD-LED TVs are only to be found in laboratories today. 

Delving Deeper into Display Technologies with YoungWonks

Understanding the differences between display technologies such as LCD, LED, OLED, and AMOLED is crucial for anyone interested in technology and its applications in everyday devices. Each of these screens has unique properties and functions, shaping the way we view digital content. At YoungWonks, we encourage learners to explore these technologies beyond the surface. Our Coding Classes for Kids offer a broad introductory framework that fosters curiosity about how coding and technology intersect. For those who want to dig deeper into programming, our Python Coding Classes for Kids provide a solid foundation for understanding the software that drives these displays. Meanwhile, our Raspberry Pi, Arduino, and Game Development Coding Classes give students a hands-on opportunity to work with hardware that utilizes these various screen technologies, making the abstract concepts far more tangible. Through these educational pathways, YoungWonks aims to illuminate the fascinating world of digital displays, equipping future innovators with the knowledge they need to thrive.

*Contributors: Written by Vidya Prabhu; Lead image by: Leonel Cruz

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