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Part Two The History and Technology of VIDEO DISPLAYS By Dr David Maddison Our introductory article last month mainly described the development of video display technology from its early inception to around the year 2000, when plasma and cathode ray tube (CRT) displays dominated the consumer space. This month, we describe the development of liquidcrystal display (LCD) screens and more recent advances. L CDs are currently the dominant display tech for static images, computers and video displays. The reason is a combination of factors: low cost, thinness, lightness, tiny bezels, colour accuracy, wide viewing angles, fast response times, high contrast ratios, reasonably low power consumption etc. But LCDs weren’t always that way. Early LCDs were small, very primitive, slow to update and only useful for devices like calculators. It took decades to develop and refine them until they were suitable for TVs. The advances haven’t stopped there; backlighting has improved, quantum dots are now on the market, and OLEDs and MicroLEDs are coming onto the 16 Silicon Chip scene, along with other more esoteric technologies like laser TVs. Before we get to those, we’ll start with the development of liquid-crystal display technology and its operating principles. Liquid-crystal displays (LCDs) Some have called liquid crystals “the fourth state of matter” [I thought that was plasma; perhaps they mean fifth – Editor]. What we now know to be liquid crystals were first observed by Rudolf Virchow in 1854, who saw unusual behaviour in myelin (the insulating layer around nerve bundles). Then in 1857, German Carl von Mettenheimer, also studying myelin, noticed it flowed like a liquid, but Australia's electronics magazine when viewed under crossed polarisers, the light showed highly coloured birefringence like a crystal. However, the material was not identified as a liquid crystal at the time. Austrian botanist Friedrich Reinitzer discovered liquid crystals in 1888 when he examined a material, cholesteryl benzoate, extracted from carrots. It exhibited specific properties when between two temperatures (“two different melting points”, as he described them) that were characteristic of both the liquid (amorphous) state and the solid (crystalline) state. In this ‘mesophase’ state, the material could reflect polarised light and rotate the polarisation of light. He siliconchip.com.au coined the term “fliessende Krystalle” for liquid crystal. See the following links for more details: • siliconchip.au/link/abfb • siliconchip.au/link/abfc In 1922, Vsevolod Fréedericksz and A. Repiewa discovered an effect now called the Fréedericksz transition that is the basis of LCD screen technology. When a liquid crystal is placed between two transparent glass electrodes, the light transmittance can be controlled electrically, like an optical switch – see Fig.27. Liquid crystals are essential to life. Cell membranes, the myelin sheath that insulates nerves, and the digestion of fats all involve liquid crystals. There was very little interest in liquid crystals until 1962, when Richard Williams at RCA Laboratories in the USA discovered the electro-­ optic properties of these materials. He found that liquid crystals formed striped patterns when an electric field was applied. In 1968, a liquid-crystal display was demonstrated by George Heilmeier, although it had to be run at 80°C. LCD materials were then developed that could run at room temperature. In 1970, a calculator was demonstrated at the international ACHEMA exhibition using an LCD screen based on Merck products. The first consumer calculator with an LCD was the Sharp EL-805, released in 1973. In 1976 and 1978, Merck developed LCD materials with fast switching times, reducing the transition time from hundreds of milliseconds to 20ms or less, and improving the optical properties. In 1980, a “viewer independent panel” display was developed by Merck that became the basis of all active-matrix LCD screens. In 1982, the first LCD TV was released by Seiko Epson in the form of a wristwatch. In 1984, Citizen released a 2.7in (6.8cm) colour pocket LCD screen, the first to use an active matrix or TFT (thin film transistor) display. LCDs were one of the first replacement technologies for CRT TVs and plasma displays. Early plasma displays could produce a larger image than LCDs but with poor brightness and high power consumption. Sharp produced a high-end 14in (36cm) LCD monitor in 1988, while Epson released a colour LCD projector, the VPJ-700, in January 1989. siliconchip.com.au Sizing and aspect ratio of TV and monitors The industry-standard way of measuring TV and computer monitor size is with a diagonal linear measurement. This is often given in inches, although European and Asian brands usually mention centimetres as well (remember when many Japanese CRT TVs were advertised in centimetres?). This has the advantage that it gives a reasonable idea of screen size for a range of aspect ratios. Using the diagonal to measure screen size has its historical origins in the days when CRTs were round but had to display rectangular images, and much of the tube was hidden by the bezel of the TV. The diagonal indicated the size of the rectangle that would be displayed, bearing in mind that the original TV aspect ratio was 4:3 (1.33:1). With flat panel displays, the diagonal measurement refers to the actual visible area. Videos come in many aspect ratios, but the most common TV, computer monitor and smartphone aspect ratio is 16:9 (1.78:1). However, some smartphones have exceeded this ratio by becoming taller. The 16:9 ratio has been a standard of the International Telecommunication Union since 1990. Standard HDTV resolutions like 1280 x 720, 1920 x 1080 and UltraHD 3840 x 2160 are all 16:9 when the pixels are square. To accommodate other aspect ratios of source material on a 16:9 screen, an image is cropped or ‘letterboxed’ (black bars at top and bottom), ‘pillarboxed’ (black bars at the sides) or, in some cases, ‘windowboxed’ with black space all around the image. The Academy standard film aspect ratio is 11:8 (1.375:1), but movies have been and continue to be produced in a wide range of aspect ratios, with 2.35:1 ultra-wide being quite popular for many years in feature films. For computer monitors, 16:10 is also a pretty common ratio (it’s very close to the golden ratio, 1.618:1), and 5:4 was also used in the past (and occasionally still is). For more information on TV and movie aspect ratios, see https://widescreen. org/aspect_ratios.shtml and for computer monitor aspect ratios, see https://w. wiki/5HtF 16 : 9 1:1 16 : 10 5:4 2.4 : 1 11 : 8 4:3 Some common aspect ratios Fig.27: the Fréedericksz transition is the basis of LCD screen technology. The shapes show the alignment of the liquid crystals in response to an electric field: a) no electric field applied, light transmitted; b) intermediate electric field applied, light partially transmitted; c) full electric field applied, all light blocked. Australia's electronics magazine October 2022  17 Research on LCD screens continued, and eventually, LCD screens could be produced at sizes competitive with plasma displays. Thus, they could be used at both the small size end of the market (where plasma displays were not suitable) and at the large size end, where plasma displays dominated. In 1994, a 21in (53cm) LCD screen was demonstrated at a trade fair in Japan. By the end of the 1990s, prototype displays of 40in/1m diagonal were being demonstrated. In 1995, Hitachi Ltd developed ‘in-plane switching’ (IPS), providing a much wider viewing angle than the existing TN (twisted nematic) technology without excessive colour or brightness shifts. Then, in 1997, Fujitsu Ltd produced an LCD with ‘vertical alignment’ (VA) technology that gave greatly improved contrast and a black screen when no voltage was applied. Most LCD screens today still use TN, IPS or VA technology. TN is mainly used where very fast response times are required as it has inferior colour reproduction and viewing angles. IPS provides the best viewing angles and colour reproduction, but its contrast Fig.28 & 29: the two polarisers in an LCD are at 90° to each other. When no voltage is applied via the thin-film transistor (TFT), the liquid crystals change the polarisation of the light passing through, allowing light to be transmitted. When a voltage is applied via the TFT, the liquid crystals align so the light polarisation is not altered and the light is blocked. Intermediate voltages cause partial transmission. 18 Silicon Chip Australia's electronics magazine is not as high as VA, so blacks can look grey. In the 2000s, new liquid crystal materials were developed with significantly reduced response times, down to 8ms, and even wider viewing angles for VA displays with better colours, brightness and contrast. In 2006, Sharp developed polymer-stabilised VA technology that gave better light transmission and thus lower energy requirements for the backlighting. In 2006, the price of LCD screens started to decrease dramatically and began to displace the market held by plasma displays, and LCD screens started outselling plasma TVs. By 2008, LCD TVs were also outselling CRT TVs. The principles of operation of an LCD matrix display are pretty simple, as shown in Figs.28 & 29. Linear polarising filters, as used on some cameras and sunglasses, ensure the light polarisation is uniform in one direction. Light is transmitted normally if two linear polarising filters are aligned. But if they are rotated 90° to each other, the light is blocked. Therefore, by controlling the polarisation of one of the two layers, the amount of light that passes through can be controlled smoothly, from near 100% to near 0%. In an LCD, a layer of liquid crystals is sandwiched between two crossed polarisers. In between the polarisers are also transparent electrodes made of indium tin oxide, with an alignment layer and colour filters (for colour LCDs) representing the colours of the sub-pixels. The whole ensemble is called ‘the sandwich’. The alignment layers consist of two polyimide plates, one on each side of the liquid crystals, which have been treated to cause liquid crystals to align with them. Each plate is aligned at right angles to the other. Surprisingly, one method of creating the alignment pattern is to rub the plate with a velvet cloth in the desired direction. When no current is applied to the liquid crystal, the alignment through the thickness of the crystal changes from the direction of one plate to the direction of the other. This causes the light polarisation to be twisted from one alignment to another, and thus, light is transmitted. If a voltage is applied through the liquid crystals, via either ordinary electrodes or thin-film transistors siliconchip.com.au (TFTs) in the base of each pixel element of the display, the liquid crystals align and block the light. The amount of blocking depends upon the voltage applied. Earlier LCD screens were ‘passive matrix’ types with electrodes on either side of the LCD layer. More recent displays are ‘active matrix’ types where the electrodes for each sub-pixel element are replaced with thin-film (translucent) transistors, resulting in a faster response time and a sharper and brighter image. The light source for LCD panels was cold cathode fluorescent light strips (CCFLs) for a long time, but it is now primarily LEDs. See the panel at the end of the article for additional comments about this distinction. Incidentally, you can tell if sunglasses are polarising or not by looking at an operating LCD screen with them and rotating them. If it goes dark or fades out at some angle, the glasses have polarising lenses. Quantum-dot displays Quantum-dot displays are comprised of two types, photo-emissive or electro-emissive. They are a form of nanotechnology. Photo-emissive quantum dots are used in any display technology that uses colour filters, primarily LCDs with LED backlighting. In an LCD, they are inserted as a film in ‘the sandwich’ made of other films, polarisers, glass, TFTs and electrodes. When light passes through a quantum dot film, it is re-emitted as a pure red, green or blue colour. The purpose is to give truer-tolife colours than is possible with LED illumination alone. LCD screens using quantum dots are said to be comparable to or superior to OLED (organic light-emitting diode) displays. However, quantum-dot displays are cheaper and can deliver superior colour at full brightness than OLEDs. Electro-emissive quantum dot displays emit light by themselves, but are experimental at this stage. They are thin, flexible displays that promise better life than OLEDs. LED and microLED displays LED displays are flat panel displays comprised of individual LEDs for the sub-pixels that are the actual light-emitting elements. They should not be confused with LCD screens siliconchip.com.au Fig.30: a Sony Crystal LED (CLEDIS) display makes up the walls in this image. The displays are modular, so they can be made essentially any size. Source: https://pro.sony/en_PT/products/led-video-walls/crystal-led-walls that use LED backlighting (see panel). LED displays are used for large outdoor screens such as at sporting or entertainment events or variable road signage. MicroLEDs are produced at a smaller size than standard LEDs and are thus suitable for smaller display devices (or higher resolution devices) than regular LEDs. These displays are inorganic and theoretically have a longer life than OLEDs, which are organic in nature (as explained below). Compared to LCDs, they potentially have a faster response time, lower power consumption, greater brightness, better contrast ratio and better colour saturation. They have not yet been mass-­ produced for smaller-scale devices such as consumer TVs, but Sony has developed CLEDIS or Crystal LED Integrated Structure that uses MicroLEDs. It is a modular system that can be assembled to make a display of almost any size for uses like public exhibitions or cinema screens (see Fig.30). In January this year, Samsung announced plans to sell microLED TVs in the sizes of 89in (2.25m), 101in (2.5m) and 110in (2.75m), but at the time of writing, they are not yet on the market. OLEDs OLED stands for organic light-­ emitting diode. Unlike traditional LEDs, which are made of inorganic semiconductors like gallium nitride, OLEDs are made of organic semiconductors. These are complex organic materials either based on small molecules or molecules joined together as polymers (plastics). These materials all have the characteristic of loosely-bonded electrons that enables them to conduct electricity to various degrees. They are known as organic conductors. The active layer (recombination region) of an OLED is electroluminescent, meaning it emits light in response to an applied voltage. Electroluminescence in organic Non-working or defective pixels in displays In matrix-based displays such as plasma, LCD and OLED screens, there is the possibility of receiving a screen with non-working pixels (also called a “dead pixel”). Possible defects include pixels or sub-pixels that are stuck on or off. An international standard has been developed to categorise the types and quantity of pixel defects that are considered acceptable, ISO 13406-2. The number of acceptable defects varies according to the manufacturer. It depends on the types of defects, the location of the defective pixels on the screen and the proximity of defective pixels to each other. Image source: https://w.wiki/5JET Australia's electronics magazine October 2022  19 Figs.31: how an OLED screen pixel works. It’s somewhat similar to a regular LED but uses organic polymer semiconductors. Among other benefits, that means OLED screens can be flexible. materials was observed in the 1950s, and the fundamental research was done in the 1960s, but Eastman Kodak developed the first practical OLEDs in 1987. White OLEDs were first produced and commercialised in Japan in 1995 for display backlighting and other lighting purposes. In 1999, Kodak and Sanyo entered into a partnership and produced a 2.4in (61mm) OLED display, followed by a 15in (38cm) HDTV screen in 2002. Sony released the XLE-1 television commercially in 2007, and in 2017, JOLED started producing OLED panels printed by an ink-jet process. A simple OLED structure consists of a protective layer, cathode (−), electron transport layer, recombination region, hole transport layer, transparent anode (+) and glass substrate – see Fig.31. More advanced OLEDs have extra layers with different regions to produce different colours. An OLED requires a simple potential difference (voltage) to start operating. The cathode has electrons (-) from the power source and the anode loses holes (the absence of an electron, +). Fig.32: Samsung smartphones with foldable OLED displays. We’ve seen reports of these screens cracking after many months or years of folding and unfolding, so do your research before buying one, especially as they are expensive. Source: Wikimedia user Ka Kit Pang, Apache 2.0 license 20 Silicon Chip Australia's electronics magazine Opposite charges are attracted to each other, and they meet at the recombination region, the boundary region between the electron transport layer and the hole transport layer. These electrons and holes come into contact forming an ‘exciton’ and emits a photon of light. This happens a large number of times, causing a continuous emission of light. A disadvantage of OLEDs is that they have a shorter lifetime than other display technologies. An advantage is that they can be made foldable, as in certain phones (see Fig.32). Fig.33: examples of Lumineq in-glass electroluminescent displays with optional touchscreen capability. The price of a taxi or Uber is displayed in the top photo, while the bottom photo shows an access code panel for a car. siliconchip.com.au Fig.34: the front of a Texas Instruments DMD chip for cinematic use. Source: Wikimedia user Binant, CC BY-SA 4.0 Fig.36: non-wobulated and wobulated images generated by the DMD. Wobulation improves the visible resolution without needing more mirrors. AMOLED is a particular OLED technology that uses an active matrix driven by thin-film transistors (TFTs). electroluminescent displays, and they are branded as Lumineq (www. lumineq.com) – see Fig.33. Electroluminescent displays Digital Light Processing (DLP) Electroluminescence (EL) is the phenomenon whereby a material such as gallium arsenide emits light when an electric field is applied to it. The colour of the light varies with the active material, but currently, the only practical displays are single-­ colour, such as yellow or orange. Displays can have fixed segments, or there can be a matrix to display any desired image. The display structure is similar to LCDs or OLEDs with striped opaque (or transparent) electrodes at the back running in one direction and transparent striped electrodes at the front at right angles to the ones at the back. One back electrode and one front electrode are energised to activate the desired segment or pixel – see Fig.35. There are two main types of EL display, either transparent or non-­ transparent, which are similar, but transparent displays have transparent back electrodes. With transparent displays, regions which are not activated are 70% transparent for matrix displays and 80% transparent for segment displays. They can be laminated within glass, such as automotive glass, and can also have touch-sensing capability. Electroluminescent displays are rugged, can operate at high or low temperatures, are resistant to high or low pressures and sunlight, and last at least 20 years. Thus, they are superior to LCDs and OLEDs in certain applications, such as outdoors. Beneq of Finland is the only manufacturer of segment and matrix DLP is a light projection technology developed by Texas Instruments (TI) in 1987 and commercialised in a projector by Digital Projection Ltd. It uses a chip with an array of micromirrors. These can be flipped into either an ‘on’ position to reflect light towards the image plane or an ‘off’ position to reflect light elsewhere, such as onto a heatsink. Although the mirrors can only be in one of two positions, intermediate brightnesses can be produced by rapidly flipping the mirrors on or off to alter the average amount of light sent to the image plane. The chip is known as a digital micromirror device or DMD (see Fig.34). The mirrors are microscopically small, siliconchip.com.au with a pitch of 5.4µm (microns, millionths of a metre) or less. The number of mirrors corresponds to the image’s resolution, except when a process known as wobulation is used to increase the effective resolution. With wobulation (see Fig.36), the DMD is moved a small amount (in both X and Y directions), such as half a pixel, to project a new subframe. This is generated by the projector firmware and half-overlaps the previous frame to give an increase in resolution without the extra expense of a higher resolution DMD. Colours are generated either by a colour wheel rotating in front of the chip, creating a series of different coloured images that the eye merges, or by three separate chips, each projecting one primary colour. The DMD is an optical MEMS (micro-electromechanical system) – see our detailed article on those Fig.35: the structure of an electroluminescent matrix (pixel) display. Original source: Electronics Weekly – siliconchip.au/link/abfd Australia's electronics magazine October 2022  21 Fig.37: the details of a digital micromirror device (DMD). Source: Texas Instruments (www.ti.com/lit/an/ dlpa059e/dlpa059e.pdf) devices (November 2020; siliconchip. au/Article/14635). In a DMD, thousands of microscopic aluminium mirrors are each supported on a yoke, itself supported on a torsion hinge between two posts and rotated about 10° between the on and off positions by electrostatic forces, as shown in Fig.37. The base layer of the DMD contains SRAM (static random access memory) cells that move one mirror by electrostatic charge according to its current state. A bias voltage is used to drive the SRAM so that when power is removed, all the mirrors reset to the same starting position, so all the mirrors move together for the next frame – see Fig.38. Due to an extensive patent portfolio, high production costs and the high level of technical know-how required, only Texas Instruments makes these devices. The DMD is manufactured according to the standard processes for MEMS and lithography, the latter described in our three-part series on IC fabrication in the June to August 2022 issues (siliconchip.au/Series/382). However, we are sure the exact processes are a closely-guarded secret. Still, we would love to know! DLP is used in some domestic projectors and about 90% of commercial movie projectors. TI offer DMD resolutions of up to 4K UHD (3840 × 2160) and frame rates from 60Hz to 240Hz with support for LED, incandescent or laser light sources. For a video teardown of an early DLP projector, see the video titled “Extreme teardown – NEC XT5000 Projector” at https://youtu.be/RzikiKqbA1U Laser TV Laser TV is a new technology, currently in the process of adoption. To generate an image, laser beams are scanned across the image plane, usually electromechanically, such as with a DLP chip. Conceptually, the image is created much like it is in a CRT, but using a laser beam instead of an electron beam – see Fig.39. The idea of laser TV was first proposed in 1966 and patented in 1977, but the laser technology was too expensive until the development of solid-state lasers. A system was demonstrated at the 2006 Las Vegas Consumer Electronics Show (CES) by Novalux Inc. In 2008, Mitsubishi Electric released a commercial 65in (165cm) 1080p HDTV model and in 2013, LG released a 100in (2.5m) 1080p consumer model. Electronic paper/ink Electronic paper is a type of display that mimics paper. Like paper, it does not produce its own light but is read by reflected ambient light. It is thus said to cause less eye strain and stress. Electronic paper can be updated reasonably rapidly, but not fast enough for full-motion video with present technology. Still, it can show slow-motion ► Fig.38: details of the individual mirror assemblies in a DMD. Original source: Texas Instruments Fig.39: a commercially-available Hisense laser TV. The image is projected from the box beneath the screen in the centre. 22 Silicon Chip Australia's electronics magazine siliconchip.com.au LCD screens: IPS, VA or TN? Fig.40: a real-time electronic paper timetable display used for Sydney buses. Source: Wikimedia user MDRX, CC BY-SA 4.0 video or frequently changing numbers, such as a clock display. Like paper, electronic paper maintains the last image written to it when the power is turned off; no power is required to maintain the display in its current state. Other names for electronic paper are electronic ink and electrophoretic displays. The name “E Ink” is a trademark of E Ink Corporation (www.eink.com). As mentioned in the text, these are the three dominant LCD technologies, although others exist. When choosing an LCD screen, this is one of the most critical decisions. While modern VA (vertical alignment) panels are said to have decent viewing angles, in our experience, IPS panels are still noticeably superior. This is especially important for computer monitors, where you usually sit close to the screen. A poor viewing angle not only means you can’t move your head much, but even with your head in a static position, the corners of the screen might appear to be fading or colour shifting compared to the centre. For this reason, we almost exclusively use IPS (in-plane switching) panels. They also tend to have the best colour reproduction, although VA screens have come a long way in that respect too. Some prefer VA panels for roles like video playback/TV or playing games because of the higher contrast ratios, ‘blacker’ blacks and faster refresh rates. However, 144Hz refresh IPS screens are now available, making the refresh rate distinction less critical. VA panels have noticeably better contrast than IPS types, but we don’t feel the trade-off is worthwhile unless they have stellar viewing angles for their class. This is a situation where it really helps to physically try out the product before you buy it, to ensure that its colour reproduction, brightness, contrast and viewing angles are to your liking. The only reason to still buy a TN (twisted nematic) screen is if you want an ultra-high refresh rate like 240Hz or higher. Again, we don’t feel the compromise is worth it as the picture looks so much worse, but some people really like these high refresh rates for gaming, in which case TN is basically your only choice. The Kindle electronic book reader is a popular application of electronic paper technology. Usage examples include electronic book readers, updateable price displays in shops, electronic signage, public transport timetables, conference badges, certain smartphones and tablet devices – see Fig.40. Electronic paper was invented at the Xerox Palo Alto Research Center Fig.41: Xerox Gyricon, the first electronic paper. Source: Xerox web page archived from 2005 siliconchip.com.au Australia's electronics magazine (PARC) in the 1970s and was called Gyricon (see Fig.41). As originally envisaged, electronic paper did not have electrodes; an image could be created by applying an external electric field in the pattern of what was to be written, like drawing with a pen. It could then be erased and a new pattern written. There are several implementation methods, but the basic principle consists of ‘Janus particles’, coated in oil or a similar fluid to enable easy rotation. These are embedded in a matrix of some sort, such as silicone – see Fig.42. Fig.42: E Ink technology. 1) Upper layer 2) Transparent electrode layer 3) Transparent micro-capsules 4) Positively charged white pigments 5) Negatively charged black pigments 6) Transparent oil 7) Electrode pixel layer 8) Bottom supporting layer 9) Light 10) White pigment 11) Black pigment. The display is about 0.51mm thick. Source: Wikimedia user FREEscanRIP, CCA 3.0 October 2022  23 When is an LED TV not an LED TV? Fig.43: a water wall projection by Australian company Laservision at an Australian event. Source: www.laservision.com.au/galleries/photos/ A Janus particle is a spherical nanoor micro-particle with different electrical or other properties on each side, such as a positive or negative charge. In the case of electronic paper, one side of the sphere might be white and the other black. The particles align with the field when an electric field is applied through or across the matrix (depending upon electrode orientation). This causes them to rotate and display either white, black, or other colours the particles have been coloured with. When the electric field is reversed, the particles rotate and present their other side. Janus particles are typically 10µm to 50µm in size. To produce colours, additive colour filters can be used. Alternatively, an electric field can control a coating of coloured oil in the so-called electrowetting process. In this latter case, a subtractive colour system is used, like with a typical colour printer that uses CMYK (cyan/magenta/yellow/ black) inks. Nearly all TVs sold as “LED TVs” are, in fact, LCD TVs with white LED backlighting. Older LCDs used cold cathode fluorescent lights (CCFL) as their backlights. TVs described as QLED are quantum-dot LCDs with LED backlighting. OLED TVs generate their own light and do not need backlighting. To avoid confusion, we would like to see the industry adopt the term “LED-backlit LCD TV” instead of “LED TV” unless it is a genuine LED TV. But manufacturers benefit from this confusion by making it seem that LED backlighting is a more significant technological advantage than it is, so they are likely encouraging it. These displays are available and suitable for experimenters and can be bought as Arduino and Raspberry Pi kits and with SPI interfaces. For example, read our article on using e-Paper displays with a Micromite in the June 2019 issue (siliconchip.au/ Article/11668). Also see the following videos below on electronic ink displays: • “Have You Ever Seen an E Ink Display Update This Quickly?” – https:// youtu.be/KdrMjnYAap4 Figs.44 & 45: a water screen nozzle sold at https://fountains-decor.ie/product/water-screen-nozzle/ The nozzle measures 930 × 528 × 802 mm and provides a semi-circular screen from a water supply of 4000L/min at 12 bar. The water film thickness is 6mm. The manufacturer did not specify the screen size that it can produce, but an example is shown. We think the semi-circle has a radius of about 10m. 24 Silicon Chip Australia's electronics magazine siliconchip.com.au • “Badger 2040 – A Raspberry Pi Pico with a Built-in e-Ink Display” – https://youtu.be/kI-_ksiYw40 • “Top 5 reasons to buy an e-ink tablet” – https://youtu.be/YKjXvjhe-Ss • “Bigme Max+ Color EINK 10.3” Note Taking Review” – https://youtu. be/RAhFzefT5DI Water screen displays A water screen is a large scale outdoor nighttime display technology where an image is projected onto a screen made of water droplets by a laser or a video projector. Water is sprayed into the air to make a waterfall or is pumped at high pressure to create a screen or a cloud of mist – see Fig.43. The Australian company Laservision (www.laservision.com.au) is a leader in this field. Unfortunately, they did not return our phone call before publication, so we can’t give any further details beyond what’s on their website. We published an article on Laservision a long time ago, in August 1990 (siliconchip.au/Article/7208). They also have the following videos available: • “Laservision Corporate Showreel” – https://youtu.be/cv04MrAJnLM • https://vimeo.com/271808280 For related products from other companies, see Figs.44 & 45. The following videos on the topic cover both home-made and commercial water projections screens: • “Homemade Water Projection Screen” – https://youtu.be/ Z7XHaKAUquA • “10’ Water Screen Projection Test” – https://youtu.be/3TPMwv2SmS8 • “Water curtains | Water Screen Projection” by Water Screen – https:// youtu.be/27YYmowUFno • “Preview 1 | Water Screen Projection” – https://youtu.be/tkCNHMvlQBk High Dynamic Range (HDR) displays High Dynamic Range (HDR) is not a type of display, but it is a set of standards designed to reflect the capabilities of new display technologies. Until HDR, video signals were designed for CRTs and could not convey video information that fully utilises the capabilities of modern displays. HDR-capable displays can show a greater range of colours, contrast, brightness, whiteness and blackness, more vivid colours, a higher frame rate of up to 120 frames per second etc. One of the critical aspects of HDR, though, is the contrast ratio of the content, ie, the ratio of the lightest areas of the picture to the darkest. Standard content has a maximum contrast ratio up to about 1000:1, while HDR content can exceed 5000:1. This better matches the human eye’s capabilities in resolving light and dark areas in the same picture. One of the key advances for HDR displays was replacing the older edge backlighting technology with LED matrix backlighting. Instead of having LEDs arrayed around the edges of the screen, there is a matrix of white LEDs behind it, and their brightnesses can be individually adjusted. This allows some parts of the screen to be very bright while others are dim, without the ‘bleed through’ associated with high brightness backlighting. The fact that the backlighting is not even is compensated for by the way the display controller drives the LCD panel itself. Typically, the more LEDs are used in the backlight matrix, the better the display’s HDR capabilities. Displays with many LEDs in the backlight are sometimes known as “mini LEDs”. Displaying HDR content HDTV and standard Blu-ray discs use 24-bit colour, which gives 16.7 million colours, but HDR content uses 30 bits for over a billion colours. This requires more data, which can be contained on an Ultra HD Blu-ray disc, although such discs will not play on standard players. HDR content can also be streamed, but you need a fast enough internet connection. If it can handle 4K video, it should be fast enough for HDR. HDR has several competing formats: Dolby Vision (Dolby), HDR10 (UHD Alliance), HDR10+ (Samsung), Hybrid Log-Gamma/HLG (BBC and Japan’s NHK), Technicolor Advanced HDR and IMAX Enhanced. Your HDR TV will need to support the particular flavour of HDR to watch HDR content. A media streaming device might be able to convert one HDR flavour into another your HDR TV can utilise. HDR10 and Dolby Vision are the most popular schemes. Note that not all 4K TVs are HDR-capable. There are also different HDR standards, with HDR10 being the most basic, but other standards may be more demanding. Still photographers can also use their cameras and software to create HDR photographs; see siliconchip.au/link/abfe among many other articles. Conclusion While LCD screens are a significant advance over plasma and CRT displays, improvements are still coming over the next few years. It seems likely that eventually, OLEDs and MicroLEDs will replace LCDs, but at the moment, they are all competitive in their own ways. That competition will drive the advancement of all these technologies over the next couple of decades unless something entirely new comes along. SC siliconchip.com.au Samsung have a 14m-wide LED cinema screen in Sydney capable of HDR content. Source: https://news.samsung.com/global/samsung-unveils-the-firstonyx-cinema-led-screen-in-australia Australia's electronics magazine October 2022  25