Displays

Does variety of displays give you a headache?

Manufacturers of digital displays and televisions go to many lengths to promote their product and to convince a consumer that their product is the best, the brightest and the fastest. However, carried away in that race, they sometimes forget that the consumer is buying the product and not the fancy terms like.In this article we took time to lay out for you in a descriptive and simple manner most important and decision-making points about displays and TVs. Today we are going to deal with only three major types of digital displays: Plasma, OLED and LCD. Keep in mind that this article is an introduction into the subject. As complex as this subject may appear to be, it consists of simple concepts easy to understand when disected. From our article you’ll learn enough to start making educated decisions about the displays you are looking at.

Plasma

Plasma displays are found mostly on larger TVs and digital signs because of "screen-door effect" - the comparatively large gap between color producing pixels – when displays are viewed the best from the distance because of the large gap between lines of pixels on the screen. The electric voltage directed to produce the "light up" effect has to be high enough to be able to excite the light emitting gas located inside each pixel, therefore pixels are placed in safe distance from each other. High voltage is also the reason why plasma displays are so power hungry. Plasmas are famous for their fast response time, bright whites, dark blacks and excellent angle view: that is why they are so popular in public places, sport bars and digital signs. Their home use, however, has been suffering decline recently due to profound increase in quality and decrease in prices of new LCDs and OLEDs. Plasma digital displays are not likely to have future in portable electronics market.

How does plasma display work?

The plasma effect is produced by the xenon or neon inert gas sealed between two layers of glass coated with clear electro-conducting electrode material. High voltage passed through the clear electrode film causes shortage inside the pixel since inert gases conduct electricity; gas turns into plasma and emits ultraviolet frequencies; ultraviolet light in turn is converted into visible frequency when it passes through the phosphorous coating on its way out (actually phosphor glows when excited by ultraviolet). Each pixel contains green, red and blue subpixels that work like little fluorescent lights. The electric charge is passed through one pixel in a row at a time because electrodes stretch all the way across the screen and it is impossible to send the signal to more than one pixel per line at one time without causing unwanted shortage in next column. The pulses are, however, so fast and well-timed by the processor that unarmed human eye is not able to recognize that whole screen is never lit up at once. If you want to visualize how it works take a picture with digital camera at quick exposure setting and you will see the bright line going across the dark screen.

OLED

OLED is the youngest type of digital displays. Organic Light Emitting Diode (OLED) sometimes is marketed as Active Matrix Organic Light Emitting Diode (AMOLED), however, today just about every LCD screen uses active-matrix addressing - more letters are used to impress the buyer - there’s nothing special about it. An OLED digital monitor operates just like plasma does - the electric impulse produces light emission - only instead of a gas an organic polymer is used, which requires less voltage and produces less heat in process. OLED technology is energy efficient; it directly emits light and does not require a backlight, allows screens to be made very thin and is an excellent fit for portable electronics where every millimeter counts. They do not produce smearing or blur during video playback thanks to fast response time. Visibility at different angles is great without loss of color or distortion. The only disadvantage of OLED digital displays for today is their high cost comparatively to LCDs and plasmas - but the gap has been rapidly shrinking. The first victory of OLEDs is expected on cellphone market. There are advances in works which promise to make OLEDs very price competitive and color balance stable. You are likely to run into Super AMOLED and Super AMOLED Plus descriptions, but keep in mind that the improvement consists of changes in subpixel patterns and is mostly a marketing move.

How it works?

As we mentioned before OLEDs use the same light-generating principle as plasmas: thin layer of organic polymers emits light (electroluminescence) when stimulated by electric charge. Because there is no multiple layers of glass with inert gas in between, they can be made very thin and compact. Plus there is no additional layer of phosphorus to convert ultraviolet into visible light - different polymers emit different visible frequencies and shades as voltage varies - it is much more efficient and simple system!

LCD

The biggest share on the market of digital displays is taken by Liquid Chrystal Digital panels - they make up the dominant majority of High Definition Digital TVs and laptop-tablet-cellphone panels.There is a variety of types and kinds but only three have substantial technological distinction: Twisted Nematic (TN), In-plane Switching (IPS) and Vertical Alignment (VA) - these are the ones we will focus on.

Twisted Nematic LCDs (TN or TN-Film)

Twisted Nematic digital panels are cheap to make and easy to manufacture. They have the best response time - as low as 2ms - amongst most of their LCD siblings, but still, can't compete with plasmas and OLEDs.The biggest downdraft of TN displays is that they produce the lowest image quality because of narrow color gamut; there are only 6 bits of brightness available which leaves makers with 64 shades of green-red-blue to play with. Couple technics allow offsetting this defect but TNs still cannot compete with the rest of flat panel technologies.Also, due to use of polarization technics angle viewing is poor and causes color-brightness shifting and wash out if you tilt the lid.

How do Twisted Nematic displays work?

In order to understand the principle of Twisted Nematic, we need to know that light is a wave and vibrates in two-dimensional, or flat, plane: left-to-the-right or up-and-down. When the wave of light emitted by the source vibrates in the single direction, it becomes polarized. The polarizing filter in TN digital panels allows only the light untwisted by the TN liquid crystal through, since the source emits the waves which filter would block otherwise - any signal which did not get turned 90 degrees is blocked by the polarizing filter and perceived as black by the eye. There are three different light sources used: a light bulb reflected in a mirror for reflective LCDs, cold cathode fluorescent lamp for LCDs, or LED, in the case of LDCs and OLEDs. The LED is the desirable feature because of its energy efficiency, smaller size and modest heat emission. A color filter placed between TN crystal and the filter, tints the light green, blue and red; three colors mixed produce different hues.

In-Plane Switching LCDs (IPS)

IPS digital displays are famous for more levels of brightness and wider viewing angles, therefore they are often favored by photographers, artists and video editors; most monitors made for color-sensitive applications are IPS digital displays. There are 8 bits of brightness are available instead of 6 amounting to total 256 levels of brightness shared between 3 (green, red and blue) subpixels. LG is the leader in this niche, though the technology was introduced to the market by Hitachi in 1996. Fancy names like Super IPS, Advanced Super IPS, and IPS Pro are simply enhanced variants of the same concept. Some of the top mobile products such as the iPad, the iPhone, the Amazon Kindle Fire, and the Asus Eee Pad Transformer use IPS digital displays. IPS technology has its own downsides, though. They aren't as bright as TN panels, and they don’t refresh image as quickly. 120Hz or higher refresh rates necessary for most 3D displays are not yet available for IPS displays, and fast-motion graphics leave a blur; they’re also more expensive in general.

How do they work?

The crystal structure of IPS displays is different, with all the crystals aligned horizontally. Unlike TN panels, where one electrode is beneath the crystal and one is above, in IPS displays both electrodes are located beneath the display, taking up more space. The design permits less light to pass through, making IPS displays dimmer than TNs. When electric current passes through the liquid crystal, the structure rotates to line up with the flat plane of the display, instead of turning vertically. The crystal turns steeper when higher voltage is applied, letting more of the backlight shine through.

Vertically Aligned LCDs (VA)

Vertically aligned displays are right between IPS and TN digital displays. They reproduce sharp colors and can display 8 bits of brightness per subpixel just like IPS displays, but they are not able to show as wide of a color gamut as IPS displays do. Viewing angles are generally are good, but not as wide as on IPS. Response times are also somewhere in between those two. Multi-Domain Vertical Alignment and Patterned Vertical Alignment are two major modifications you will hear about. Today VA displays show excellent blacks and deliver very good contrast ratios.

How VAs work

A Vertically Aligned panels are similar to a TNs; only the crystal structure is different. When no electric current is applied, the crystals remain perpendicular to the display blocking all light from the backlight. When a charge is applied, the crystals realign horizontally, allowing light to pass through.

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