Media Notes / Display Technology

Following

• CRTs shoot an electron beam at phosphors coated on a screen. When an electron beam hits a phosphor, it glows for a moment then fades, typically in microseconds. Because of the way our eyes work, what we see is a whole image rather than a stream of light racing across the screen. This is also the only display type primarily used for analog signals. How this is used depends on the application:
  • Raster scan CRTs creates an image that fills the entire screen at a rate of at least 50 full images per second, topping out at 160 or 180 per second for high-end VGA monitors.
  • Vector scan CRTs directly steer the beam, like an artist drawing the image. However, this is only limited to line graphics with no fill and most times, no color. While it saw limited use for video applications, it remained prominent in oscilloscopes.
  • Digital displays. The only known application of this is the Nimo Tube. The CRT beam isn't focused as tightly and is instead directed towards one of several masks that create the image. For Nimo Tubes, they were meant to be a competitor to the Nixie Tube.
• To produce color, red, green, and blue color producing phosphors are laid out on the screen, typically requiring an electron gun for each. In order to prevent stray electrons from hitting the wrong phosphor, a metallic "mask" is typically used. Later in CRTs life, a method known as Beam Indexing came about, which used two different phosphors to send feedback to a light detector. This feedback meant that the CRT could use one electron gun, using the feedback to switch over to a different color. But since the quality of this wasn't as good as masked CRTs, its applications were limited.
• CRTs do not have discrete pixels. While the masking pattern of a CRT suggests there may be pixels, they're arranged in a way either doesn't make sense, such as in slot masks, can be interpreted in different ways, such as a traditional shadow mask, or the phosphors are just a line from top to bottom, such as with the mask in Sony's Trinitron displays. In addition, the electron beam isn't perfectly focused and is continuously varying, meaning it may be hitting multiple phosphor groups and/or partially hitting a phosphor.
• A common effect when filming a display using CRT is black bands that slowly scroll down. This is because the filming rate (usually 24FPS) only captures some of what the CRT is showing at the time. Human eyes exhibit what's known as persistence of vision, which retains 10s of milliseconds of what they registered.
• There were some applications that took advantage of some of the quirks with CRTs
  • Light Gun Games from the mid 80s to about the mid 2000s figured out where the player was aiming the gun by taking the difference of the start of a frame and when the light gun detected it picked up light. Though a noticeable effect of this was that the screen had to flash white, or at least be of a bright color. When LCDs and other digital displays came to market, this method no longer worked mostly due to input lag (though changing the image all at once hurt it as well). Since then, light guns resorted to using IR LEDs and sensors to determine how the the gun was pointed.
    • NES light gun games worked differently. Rather than using the above method, the screen goes completely black for one frame, then cycles each target with a white box each frame afterwards. This method was supposedly to combat cheating by pointing the gun at a light source, since the gun had to reset itself by seeing a blank screen first.
  • The brief electrical persistence of points drawn on a CRT is also what allowed modified CRTs known as Williams tubes to be used as a primitive type of dynamic memory by several first-generation mainframe computers in the early 1950s.

• Practically no input lag, thus perfect for Video Games.
• Little, if any, motion blur due to pulse-based screen refreshment, as opposed to the sample-and-hold method in LCDs and OLEDs.
• Theoretically infinite contrast ratio since the phosphor isn't activated for black. Practically, the black level depends on the ambient lighting conditions.
• No native resolution, thus no loss of sharpness when switching to most supported resolutions. (And no, the shadow mask does not define a native resolution for a CRT.)

• Most famously, CRT screens are subject to burn-in.
• CRT displays are bulky, heavy, power consuming, and they run hot, especially the tube itself. This stems from the fact that a CRT needs a very high voltage, anywhere from thousands of volts to hundred thousands of volts, in order to fire its electron guns. This causes some issues of its own:
  • CRTs are hazardous to work with or around as the voltage is generated via a bank of capacitors. Without a bleeder resistor, it can take a long time for the capacitors to discharge. The high voltage from the supporting components carries enough punch to knock a careless engineer across the factory floor and can cause cardiac arrest to those already suffering respiratory problems. They're definitely not to be reckoned with if you don't know what you're doing (and sometimes, even if you do - a second's worth of distraction is all it takes to make that tiny mistake and be jolted with thousand of volts of electricity). We think it's worth repeating - do not leave a CRT display running without its back cover screwed on, heck, do not remove the back cover of a CRT TV if you don't have a reason to, and leave the repairs to the professionals. And even then, keep a safe distance from engineers who're repairing a CRT display.
  • The high voltage going through the coils in the flyback transformer more than often results in a distinctive high-pitched whine. While effort has been made to reduce the loudness of the whine over the years, even by the end of the era of CRTs the problem had not yet been completely eliminated.
• Maximum brightness is limited to protect the tube in consumer applications. Running a tube on very high brightness is possible, as seen in CRT-based projectors, but the lifespan of the tube would in turn be relatively short. The tube would also become very hot, necessitating a noisy active cooling system. CRT displays for consumer use were designed to only need passive cooling, and part of the trade-off needed to achieve this requirement is to limit the power of the electron gun, and thus the brightness and contrast levels.
• Subject to flickering if the refresh rate is too low. Interlacing makes this worse, as it effectively halves the refresh rate to double the vertical resolution.
  • This is why most people who claim to get headaches or eye problems from CRTs have them, especially if the room was lit with fluorescent lights, which have a 120hz flicker (in the United States) from the AC power. The CRT's 60 Hz refresh rate could interact with the light's flickering in such a way to exaggerate the flicker of either. Setting the refresh to 72hz or more made the display clear and stable. It's even worse in Europe, Asia and the Pacific, where the AC cycle is 50hz, which makes the flickering more pronounced.
• Image geometry can be distorted as the phosphor screen is curved (even on so called "flat" displays), often in a way that cannot be corrected by the On-Screen Display (OSD) menu.
• Color convergence can be thrown off, resulting in color fringing.
• Since CRTs contain what is essentially a linear particle accelerator, the screen can generate a non-trivial amount of X-rays, especially in color sets. CRT glass is leaded to protect against this, but the lead makes disposal a problem and adds to the already-unwieldy bulk of large tubes. Also, the lead protection can not eliminate it completely, but only reduce it to minuscule amounts.
• Holding a strong magnet against the screen can permanently damage it by twisting or distorting the shadow mask (a piece of metal that keeps the colors separated) behind the screen. Light magnetic distortions are normal due to the Earth's own magnetic field, and are fixable using via degaussing (most CRTs have a built-in degaussing coil, and will automatically use it when powered up). However, if a TV is sent across long distances, chances are it will face gaussing problems too great to be fixed by the built-in coil and will need to be fixed by a trained engineer with a degaussing wand.
  • Old monochrome CRTs don't use a shadow mask, making it safer (though still not a good idea) to use strong magnets on their faces.
• Another issue is that the electron guns can become less effective as contamination builds up over time. One way to fix this is to run the CRT through a rejuvenator, which applies a high voltage on the electron guns to "burn off" the contaminates. While this can restore the image quality of the CRT, CRT rejuvenation can typically only happen once as it also affects the physical integrity of the guns. Basically, the outcome is either the CRT becomes unusable or it works for some undetermined amount of time.

YMMV

• While CRTs don't have native resolutions, they do have maximum resolutions, although this is artificially imposed to protect the tube. Going to higher resolutions than recommended may cause the image to shimmer and appear blurry, the tube runs hotter, and in a long run, shorten the life of the tube. This is why smaller CRTs has a lower resolution limit than the bigger ones (the last CRT displays in the market could handle a maximum of 1024x768 at 15 inches, while tubes that could handle a full 1920x1080 were at least 25 inches in size. Comparatively, the typical modern LCD or OLED panel can handle 2560x1440 at a little over 5 inches). The use of a moving beam also means that there is a limit as to how fast the screen can refresh, with higher resolutions negatively impacting the refresh rate. Old computers and video game consoles that were designed for use with NTSC and/or PAL TV sets or dedicated CRT monitors with similar operating frequencies tended to have fairly strict upper limits on vertical resolution, partly because of video memory constraints but also because the standards specify a total number of lines in each frame and at least some of those lines must be reserved for vertical blanking periods.
• It took CRTs many years to get to the point where they have great color quality with true black. Early CRTs had a silver emulsion on the glass surface and thus black looked silver on those sets under normal lighting conditions and the room has to be darkened to a certain degree, or a sheet of tinted glass has to be placed in front of the screen, to get good black levels. CRTs made with tinted glass was experimented on in the late 50s and went into production in the 60s, but were considered too expensive to be put into consumer television sets and thus were only found on computer equipment. The price of tinted CRTs only fell low enough in the early 80s, which saw the first television sets with tinted CRTs roll off the conveyor belt (and even then the display is not tinted as heavily as CRTs made for computers. A CRT of a TV is still tinted lightly enough that it can be inspected with an inspection microscope without being switched on. A CRT made for computers, can’t). The 80s also saw a switch from silver emulsion to a dark grey one, further improving black levels. Color calibration then came in the late 80s, spearheaded by Apple who advertised their machines as the perfect electronic desktop publication computer.
• The dot pitch of the mask or grille also plays a part in the clarity of the image on screen, especially at high resolutions. The finer the dot pitch, the better as it means the image is sharper.
• The blurriness can be seen advantageously as an antialiasing effect. Combined with the scanlines and phosphor pattern, it can give the illusion of looking at a higher resolution image through a fine fabric or grille of sorts as your brain fills in the gaps. Example here. And because the image is continuous horizontally and discrete vertically, more sharpness is preserved compared to the typical bilinear filter, which blurs the image in both dimensions. Retro gamers hence often claim old pixel art looks better on CRTs.
• Before the advent of the intelligent self-degaussing circuit, CRTs had to be specially degaussed in a “gravity room” or “magnetic booth” in the TV factory where the magnetic characteristics in the booth could be adjusted based on which area the TV would be sent to, and the TV then degaussed to meet the area’s requirements. This is why older CRT based TVs start having gauss problems and had to be degaussed again when they are shipped from one region to another. Thankfully, modern CRTs no longer need this and most sets from the late 90s on will automatically do a degauss pass on power up and let the user trigger another degauss when needed.

• Made of individual plasma cells. Like CRT, the screen is coated with phosphors that glow, but instead of being excited by electrons, they glow from plasma generated in the plasma cell.
• Based on the same principle as the neon light; early plasma screens were monochrome and glowed with the bright red-orange color of neon.

• Usually very bright with the highest contrast available.
• Excellent color quality.
• Flickering is practically non-existent, due to the panels refreshing at a really fast refresh rate of up to 600 Hz in some models
• A relatively thin profile, comparable to most LCDs of the same size at the time.
• Very good black levels (Effectively 0); the Pioneer Kuro line even has its main selling point right in the name!

• Uses discrete pixels.
• While marketers would advertise sets as having a refresh rate of 600 Hz, this only applies to the refresh rate of the plasma cells themselves. The input signal most of the time was limited to 50/60 Hz.
• The front panel is glass (subject to breakage) which makes plasma displays deceptively heavy.
• Plasma displays run hot and consume lots of energy. Modern displays though are approaching similar power consumption as early LCD sets.
• Subject to image burn-in, though modern displays aren't as bad as early ones.
• As of 2014, pixel density appears limited. One needs to buy a 50" TV before reaching 1080p.

• Similar to plasma, but built on vacuum tube technology rather than the neon light. Phosphors painted in patterns on the back of the tube are excited by electrons emitted from a filament just behind the screen. A set of grids between the back and the filaments allow control over various areas of the screen; this allows for LCD/LED-style multiplexing.
• Usually monochrome, specifically a pleasing turquoise color (though Sony has sometimes used a more whitish phosphor on their VFDs).
  • However, since it's based on phosphor technology, it is possible to have a VFD with multiple albeit segmented colors, as seen in various electronics from the 80s (i.e. the spectrum analyzer on some stereos, or the record icon on some VCRs). Read: a VFD can show multiple colors, but the color of a segment on the VFD cannot be changed once it's manufactured.

• Very bright and readable, even in bright light.
• Will run well in cold temperatures, making them popular for automotive use (digital dashboards, radios, and such).

• Uses more power than LCD or LED-matrix displays, but not quite as much as plasma.
• Limited range of colors available; almost all VFDs use the same few shades of turquoise, white, red and orange. Blue VFDs are usually achieved by passing White through a color filter, true blue VFDs are rare and expensive.
• Not as thin as LCD or LED-matrix displays.
• Like all vacuum tubes, they're fragile and the filaments have a limited life. However, since the filaments don't need to be run hot, their lifetimes can be very long (decades).
• Due to limitations of the manufacturing process of VFDs, it's not possible to have a full color dot matrix VFD, let alone one capable of going beyond low-resolution graphics.

• They work just like plasma screens, but instead of individual pixels, fully-formed numbers (Nixie) or seven-segmented digits (Panaplex) are used.
• Very common in older digital equipment from the 1960s and early 1970s.

• Largely the same as modern plasma screens; these were the brightest small displays around until VFDs and LED-matrix screens became popular in the late 1970s.

• Require high voltages to work, making them impractical for battery-powered equipment (though some people have done it anyway).

• Similar to DLP, it uses a microelectromechanical-system (MEMS) chip to reflect light. Unlike DLP, it works just fine in ambient light and doesn't require a color filter, as each MEMS element is designed to reflect a specific wavelength of light (which is where that Techno Babble name comes from). While it was used in a smart watch (Qualcomm's Toq), it appears the technology's demise was due to Executive Meddling. The company and patents were purchased wholesale by Apple who proceeded to sit on the technology and thus killed it.

Pros

• Very good visibility in bright light.
• Can retain state without power, or at least using very little power.
• Small enough that the final major manufacturer of this technology used it for a smart watch.
• Decent refresh rate, at the time the technology was abandoned the displays had a 60Hz refresh rate.

• Poor color reproduction, most press coverage reports that the colors on all the displays looks washed out.
• Extremely power hungry in constant motion applications (ie video, gaming with lots of onscreen action) when compared to alternative technologies like LCD panels and OLED displays.
• Useless without a light source, and due to design, cannot be backlit, meaning low-light applications are constrained to front-edge lighting which has poor brightness uniformity.

• Field Emission Display (FED) and Surface-conduction Electron-emitter Display (SED) both use a miniaturization of the CRT: instead of one or three electron beams hitting a phosphor coating, have every sub-pixel contain its own electron beam.
• Development happened during the 2000s, but by 2009-2010, the writing was on the wall that LCDs were the best bang-for-the-buck, plasma was still viable, and the then-emerging OLED was looking promising. The companies that were working on FED and SED announced they were dropping further development.

Scanning LED

• A scanning LED consists of a single row of LEDs that change rapidly, while either the row of LEDs moves rapidly or something else, like a mirror or a moving object projects the "image" the LEDs are displaying.
• A famous example is the VirtualBoy, using a single row of LEDs and a mirror that moves back and forth to provide the illusion of an image.

• The display has a material called liquid crystal, which twists light into a certain direction depending on the voltage applied to it. By sandwiching the liquid crystal element with polarizers to only allow light of a certain direction to pass, liquid crystal can either block light or let it through.
  • Reflective LCDs use ambient light that's reflected back to the user while the liquid crystal blocks or allows some of that light back. Used in very low power consuming devices but has the problem of requiring a good light source to see well. Front lights can either be embedded or bought separately. The Game Boy and Game Boy Advance used reflective LCDs.
  • Transmissive LCDs use an always-on backlight that shines behind the liquid crystal component. While these tend to be lower power consuming than other display types, it works poorly in bright light. This is the most common type of LCD you'll find in consumer electronics.
  • Transreflective LCDs have a transreflective layer that reflects ambient light coming into it while letting light from a backlight pass through. This lets the display be readable under any lighting conditions, but compromises on image quality.
• Depending on how the polarizers are arranged, "on" can either be black or white. The most common configuration is black is the "on" state, which means that LCDs consume more energy opposite to what one might expect.
• Backlit LCDs used to be lit by cold cathode fluorescent lights. LEDs now provide the backlight for backlit LCDs. These come in two arrangements:
  • The LEDs can be on one or two edges of the display (Edge Lit) and the light is as uniformly distributed as possible across the display. Certain sections of the edge can be turned on or off for cheap zone lighting, but this often results in a distracting column of light when viewing certain scenes.
  • The LEDs are spaced evenly behind the LCD itself (Array). Some array-based LEDs can be individually dimmed to increase contrast between dark and light areas, called local dimming. Thanks to shrinking LED technology, the number of local dimming zones has gone up to around 1,000 for higher end TVs and monitors, to claims of up to 10,000.
  • Confusingly, LED-backlit LCD displays are sometimes sold as "LED displays." It's already enough that LCD and LED are similar acronyms, and that most people who just want a decent TV or monitor might not care to know the meaning of the acronyms. However, this means that someone who doesn't know about LED-backlit LCD panels might be misled into thinking they are buying an LED array, OLED, AMOLED, or other purely LED technology display.

Pros

• Currently the cheapest, most versatile display technology available.
• Thin and light profile. Suitable for portable displays.
• On average, consumes the least amount of energy.
• Excellent refresh rate and still improving. Active 3D is possible on 120Hz or higher panels. The fastest panel as of 2023 has a 500Hz native refresh rate.
• Using a specialized polarizer, it's possible to have Passive 3D^note 3D that polarizes each alternating scanline differently such that viewing only requires glasses with special polarised lens or even Autostereoscopic 3D ^note 3D without the need of any glasses whatsoever.

General Cons

• Uses discrete pixels.
• Pixel response time is higher than most other technologies. Average response time is 8ms-16ms using the ISO standard test of full black to full white, with 2ms-6ms from gray-to-gray. Longer response times cause a smearing effect known as ghosting.
  • This is worse with passive matrix displays. However, encountering a passive matrix display in a modern electronic device is rare and mostly relegated to really low power devices or devices that only need simple outputs like a pocket calculator.
• Some LCD panel types have narrow viewing angles which cause color shifting if not viewed head on. Though if the screen is too large, color shifting can still be perceived regardless of viewing angle.
• Old or cheaply made LCD panels tend to have a problem with image persistence.
• All LCDs use a light polarizer in order to guide the light in a way that makes easy for the LCD to block light. This presents two problems:
  • If a linear polarizer is used, this will cause the screen to look blank with polarized sunglasses unless the display or sunglasses are rotated to a certain angle. Though some people have taken advantage of this by removing one of the polarizers and making glasses out of them as a privacy filter.
  • It may become loose or degrade over time. On reflective LCDs this results in brown spots showing up on the LCD and nothing can appear in the spots, while on backlit LCDs the screen would look normal when not powered, but will have white spots showing up with nothing appearing inside the spots when the screen is in powered state - this is known in the hobbyist circles as "screen burn", as it tends to happen to LCD devices that has been stored in high-humidity, high-temperature areas (for example, a non-air conditioned store room in a house in equatorial climate regions). In extreme scenarios, the degradation may present itself as bubbling and/or cracking on the screen.

Cons specific to backlit LCDs

• It's impossible to show "true black" due to the backlight being always on and the liquid crystal itself being unable to perfectly bend light to be blocked by the front polarizer.
  • Displays with dimming zones can help increase the contrast ratio of high-contrast scenes, but they also have an issue with haloing if the content is much smaller than the zone size.
• The brightness of backlights may be controlled via PWM, or the backlight flickering on and off (or mostly off) at a rapid frequency. This can cause headaches for some people who are sensitive to flickering. However, higher-end displays such as those marketed for gamers may allow the user to enable this to reduce motion blur at the cost of reduced brightness.
• As backlit LCDs use a light diffuser to evenly distribute the light, this may over time become damaged or loosened. This can cause bright spots on the LCD to show up.
• The temperature of LEDs in some edge lit displays can get extremely hot, well above 100C, if ran at maximum brightness. This can cause the light diffuser to crack or melt, creating streaks of light at the bottom of the display. Or worse, burn out the LEDs.

YMMV

• LCDs may come in glossy or matte finish.
  • Glossy finishes offer a clearer picture, but there is bad glare in bright light.
  • Matte finishes have excellent glare reduction in all lighting conditions, but may appear fuzzy.
• LCDs may have a glass covering over it to protect it. Consequently this makes it subject to cracking if the display takes a hard hit. Though glass is normally used in high-end applications. Otherwise plastic is used.
• Color accuracy actually depends on how the panel was built, not by how many different shades of color it supports (though that definitely helps). Color accuracy is determined by how close the panel can hit certain points in a given color space. So even a TN panel, considered the worst of the panel types, can have more accurate colors than a IPS panel, which is considered one of the best.

Panel Types

• Twisted Nematic (TN)
  • Comes in two varieties: Passive Matrix (which is very prone to ghosting and has very poor refresh rates) and Active Matrix (eliminates blurring but costs more).
  • Pros: Offers the best response time and is the cheapest to make
  • Cons: Limited to 18-bit colors (using tricks to fake 24-bit), has the narrowest viewing angles, and contrast ratios are the poorest. It also can't be used as a touchscreen without a hard covering due to distortions at slightly modest pressures.
• Vertical Alignment (VA)
  • Pros: High quality color and offers the best contrast ratios, topping out at 8000:1 in some of the highest-end TVs
  • Cons: Viewing angles are only slightly better than TN, making it unsuitable for viewing it off axis.
• In-Plane Switching (IPS), also known as PLS in Samsung models and AHVA in AUOptronics panels
  • Pros: High quality color and offers the best viewing angles.
  • Cons: Contrast ratio is barely better than TN, with the best models topping out at about 1000:1. It also has the dreaded "IPS Glow" where parts of the screen have a significant amount of backlight bleed when showing dark content (though this is only noticeable in a dark environment).

• A huge array of addressable RGB LEDs arranged in a matrix that, if viewed from a distance, produces an image. These are commonly used for video billboards (both outdoor and indoors) and video scoreboards in stadiums, but Samsung is experimenting with using them as an alternative to projectors in participating movie cinemas. Oftentimes the LEDs would be grouped into panels, and multiple panels in turn grouped to form a display. This technology is actually dates back to the 70s and was a popular fixture on Pinball tables in the late 80s and 90s.

• Very good color reproduction, true blacks and very bright whites.
• Reasonably high refresh rates, fast enough that Active 3D is possible.
• Burn in, while possible, takes a very long time to show up.

• Uses discrete pixels.
• Very expensive as it requires a large amount of addressable RGB LEDs, which itself isn't cheap. A 4K Samsung Cinema panel has about 8.85 million individual aRGB LEDs on them, making them very costly to install or replace compared to conventional projection systems. one source estimates a screen to cost between US$500,000 and US$800,000 depending on features- two to three times the cost of a equivalent digital cinema projector.
• If repairs are performed, the new LEDs may shine brighter than the older ones, resulting in an uneven image. In a cinema application, the entire set of panels have to be replaced to maintain color uniformity.
• Viewing from close up destroys the illusion. The panels has to be seen from at least a minimum distance to produce the illusion of a coherent image. Using a diffuser (a sheet of white mostly opaque plastic) in front of the panel can help alleviate the problem, but not eliminate it completely.
• Size. These panels are built on existing aRGB LED technology and thus are quite huge in relation to their resolution.

• Projectors shoot bright light through a lens to project an image onto something, typically a special screen or a flat wall. This makes them flexible as to where you can put them and as long as the surface is flat and of a neutral color, ideally white.
• The light source commonly used in projectors are either LEDs, lasers, and halide-based lamps for smaller projectors, to arc lamps used in massive theater-sized ones.
• There's several ways projectors create an image:
  • LCD type projectors shine the light through what's essentially a miniature LCD panel.
  • DLP (Digital Light Processor) types have 1 or more chips that have microscopic mirrors that adjust how much light gets put out. In 1-chip types, a color wheel spins around while the chip rapidly changes to effectively create multiple single-color images, and our eyes blend the result together, but this results in the so-called rainbow effect where you may be able to see each individual color image. Multi-chip types shine light through their own color filter.
  • In either LCD or DLP, the light source can either be a bright lamp or lasers. Laser type projectors come in one or three laser varieties. In the single laser variety, a blue laser shines through a yellow phosphor, which creates perceptually white light that can be used. In the three laser variety, red, green, and blue lasers are used to create the primary colors, though this is usually only used in DLP projectors.
  • There are CRT based ones as well, using one tube for each color, with a lens to enlarge it onto the screen. CRT based ones need to show a much brighter image than what was normally shown on a CRT based TV, which led to the tubes not lasting as long. In addition, they were more bulky due to the size of the tube itself, the lens needed to enlarge the image, and the focal distance to make sure the image is clear. They also needed both an onboard active cooling system and air conditioning as opposed to other projector technologies. As a result, CRT based projectors were rarely used outside of small to medium commercial establishments (ie Karaoke bars) and early in-flight entertainment systems.
• Occasionally short-throw projectors (those that work best close to the screen) were built into standalone units, resembling a bulky TV. These are sometimes referred to as rear-projection TVs.
• As a home project, you can turn your cell phone into a projector by enclosing it in a box and putting a magnifying lens at a certain distance away from the phone. It won't be very effective (it'll be much darker than just viewing the phone's screen), but it also is a good way to show how projectors work in general.

Pros

• The screen is anything you want it to be, which means you can project images to say the front of your house if you wanted to.
• The size of the image can be as big as you need it to be.
• Consumer grade projectors are small enough to be carried around to most places. As mentioned, some projectors can be made small enough that phones had them or can be made into something as small as one.

Cons

• Projectors that use lamps run hot enough that they need a fan to prevent the lamp from overheating. This fan can get loud enough to be distracting. LED and laser based ones may not need them. If the projector has a fan for this purpose, it also needs a cool-down period after being turned off. Disconnecting power suddenly may cause the lamp to fail.
• The room used for a front projector must be as dark as possible or the contrast of the projected image will severely suffer. Basically, the "black level" of the projected image is going to be the darkest part of the surface you're using for the screen. Additionally, the area that is to be used for the projection screen must be matte bright white and as smooth as possible, but not reflective, to achieve the best possible image quality.
• Setting up a projector is more hassle than other technologies. The projector's distance, angle and focal point must be carefully adjusted or the picture will be distorted. While the higher-end projectors offer automatic keystone and focus adjustments using various technologies, the measurements tend to be inaccurate still need manual fine-tuning. This compared to the CRT and LCD display's "plug and play" setup. In fact, this is actually the only barrier that puts people off buying a projector as of 2023 - while projectors are now so cheap that they can compete with the price of a LCD TV, not everyone has the patience needed to set one up. In addition, you need a projector screen of some sort, adding to the cost and may limit where it can be setup.
• CRT projectors were bulky, heavy, consumed a lot of power and generated a lot of heat because of the fact that there are three extra-bright tubes- one of each primary color- projecting the image onto the screen. In addition to this, they were also expensive to maintain as the tubes have to be replaced frequently due to the high brightness they were usually run at, they were noisy due to active cooling, and even then they needed a sufficiently air-conditioned room to run optimally, color fringing is a problem if one or more of the lens got misaligned, and to top it all off, they share some of the design issues with CRT TVs (namely, flickering and maximum resolution limit).
• DLP based projectors can cause motion sickness and nausea in some viewers due to the way it works. These viewers will also perceive something called a “rainbow strobing” effect occasionally.
• Laser based projectors require special non-reflective screens to function properly, otherwise the viewers may observe something called laser speckle, where bright scenes would result in shimmering and colored dots on the screen
• Halide-lamp based projectors need a warm up period before the lamp reaches its maximum brightness.
• Arc lamp based projectors aren't consumer friendly at all, requiring high-voltage power supplies, careful handling ^note Touching one with bare hands will cause the lamp to catastrophically fail, due to oils degrading the integrity of the glass when the lamp gets hot. This is similar to a problem with halogen bulbs, and older mercury based arc lamps generating enough UV to burn skin and eyes with brief exposure (most are xenon based now).

• The screen comprises of electromagnetically sensitive ink suspended in a fluid. When given a voltage, the ink moves from one side of the cell to another, which changes how much light is reflected back. The principle is old though, Magna Doodles (a 1974 children's toy) used a similar technique.
• Another name for this technology is electronic ink or e-ink.

• Lowest power consumption. Electronic paper retains its state even without power and it only needs power to change the image.
  • Some models are shipped with a welcome image set from the factory ready to be seen on unboxing, while expected battery life for dedicated readers is measured in days or even weeks.
  • Stores have switched to using e-ink based price tags to not only make updating the price easy, but tags no longer have to be moved around based on the product, since the tag can be updated to show the product's name as well.
• Thin profile. Typically used in portable E-Book readers
• Modern black and white electronic paper screens are easily capable of the equivalent of 300 DPI resolution, which is the standard printing resolution.

• Only useful for showing static images as response time is very poor. Android-powered devices require some vendor-specific customization and apps to sidestep the response time limitation.
• Electronic paper has low contrast ratio, achieving only as high as 15:1. To be fair, consumer ink jet printers are only capable of 50:1 at best on glossy, photographic paper and electronic paper is intended to mimic print media.
• While color electronic paper is possible, color quality is not quite as good as other display types and total resolution of the display suffers since most forms of it use a black-and-white screen with color filters.
• Has issues with image persistence, requiring the display to reset itself by going full black and full white every so often.

• This display consists of organic compounds (which in this instance means the compounds contain a hydrogen-carbon bond somewhere) that can produce bright light when given a voltage. This can then be deposited over a screen in such a way that each pixel or subpixel gets its own light source, rather than relying on using a single light source that's diffused across the panel.

• Very thin profile, down to millimeters. This allows flexible and semi-transparent displays to be built.
• As with CRTs and plasma displays, OLED has theoretically infinite contrast ratio due to black simply being "off". As with the other two technologies, the practical black level depends on viewing conditions and how the display was manufactured.
• The compounds that make up an OLED display can be printed via inkjet technology. This can help reduce the cost of manufacturing.
• Compared to LCDs, it has the best viewing angle and theoretically the best lighting uniformity.
• Faster response times compared to LCD, with reports of around 0.1ms to 1ms. Note this doesn't completely eliminate motion blur due to sample and holding.

• Uses discrete pixels.
• Subject to burn-in
  • Modern OLED displays combat this by either limiting brightness, shifting static elements around, "conditioning" the panel once in a while, and/or adding elements to improve light transmission efficiency.
• Can't sustain the same maximum brightness as LCDs, though there are some methods to address this:
  • Adding an active cooling system to the OLED elements.
  • Using microscopic lenses to help better focus the light
  • Stacking another OLED display on top, known as tandem OLED.
• Energy efficiency isn't as good as LCDs, but it depends on the content being shown. Some OS and apps offer dark mode to take advantage of this.
• Blue OLEDs have an issue with both lifespan (16,000 to half-brightness vs. 60,000 of other technologies) and efficiency at high brightness.
• Will be damaged upon contact with water, including the humidity in the air, thus the display has to be sealed.
• Flexible displays are more fragile than rigid ones, at least in the applications they're currently being used in (i.e., folding cell phones)
• OLED panels require regular maintenance to keep good perceptual image quality for as long as possible. This maintenance comes in two flavors:
  • Pixel refresh, sometimes called RS compensation. This is to fix image persistence issues and usually takes 5-10 minutes. This is normally triggered when the display has been on for more than 4 hours and the display goes to sleep.
  • Panel refresh, sometimes called JB compensation or "Pixel Cleaning" in LG displays. This is to account for uneven wear of the OLED elements themselves. This effectively wears out all of the pixels to achieve perceptual panel uniformity. As such, this should only be ran on the manufacturer's recommendation or if the display tells you it needs it.
  • Note that if the display is constantly on or is immediately unplugged or always has a hard power off after using, it likely never runs either maintenance operation.

• A lot of consumer OLEDs use a PenTile Matrix to arrange the subpixels so that there are more (smaller) green and red subpixels and fewer (but larger) blue subpixels. This may give the display a subtly odd hue compared to other displays. Non-uniform subpixel arrangements are used to make OLED colors that wear out faster (like blue) larger so they wear out more or less evenly in brightness compared to red and green.
• Another sub-pixel arrangement, mostly used by Samsung in their QD-OLED panels, arranges the RGB elements in a triangle pattern. This can lead to color fringing and a decrease in text clarity, but it's mostly a problem with UI-type content.

• A particle called a quantum dot, when exposed to blue light, starts to glow and give off light itself. However, the color of the light depends on the size of the quantum dot. The principle is similar to how neon and fluorescent lamps work, but colors are managed based on the size of the particle, rather than the gas being used.
• Typically a monochrome LCD or OLED panel drives the quantum dot sub-pixels, replacing the color filter if there was one.
• Another application of quantum dots is to directly drive them using a principle similar to electroluminescent displays, called QDEL. QDEL displays as of 2024 are in the prototype stages, but is a competing technology with microLED.

Pros

• If a QD layer replaces the color filter, this allows for more efficient use of the backlight since the QDs emit light themselves. While it's not a 1:1 conversion, a lot more of the original light gets through than a traditional color filter.
• Color accuracy tends to be consistently good, since the QDs are producing a pure shade of the color. This is opposed to using a backlight that actually doesn't produce a uniform white light^note Most white LEDs are blue with yellow phosphors and it only appears white to our eyes. Their light emission peaks at blue and has a hump that isn't as strong around yellow and using color filters that can't block 100% of light that isn't the color of interest.
• Quantum Dots are relatively easy to create with the desired properties, as synthesizing them is mostly a chemical process that can be done with basic lab equipment.

Cons

• QD-OLED displays tend to use a triangular pixel arrangement. Because most software expects square pixels, this causes issues with color fringing on edges of color.
• QD-OLED displays don't use polarizers, unlike QD-LCD ones. Because polarizers can filter out light, this causes QD-OLED displays to reflect more ambient light. In addition, ambient light can activate the QD layer, which can raise the black level of the display even in dimly lit environments.

• Individual LEDs are built on a microscopic scale, each LED being a pixel itself. It's similar to the abovementioned large LED Array- based displays found on video billboards and video scoreboards at stadiums, but in a more practical size.
• Would have very good contrast ratios comparable to OLED and higher brightness than OLED, and darker blacks than plasma.
• Reasonably high refresh rates, fast enough that Active 3D is possible.
• Burn-in, while possible, could take an impractically long time to show up.
• Irreparable. Due to the manufacturing process, if one of the MicroLEDs on the panel develops a fault or defect, the whole panel has to be replaced.
• Uses discrete pixels.
• As with many new miniaturized technology, the launch price is expected to be extremely unaffordable- exponentially higher than the large aRGB LED Array solutions that are available today, although the price will go down in time. Most predict that for the first few years the technology will only be used in commercial applications like smaller video billboards, professional displays and maybe arcade cabinets.