Televisions.

Plasma Televisions
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Plasma HDTVs have generally been a more expensive technology than LCD displays, but this gap is shrinking. Plasmas offer benefits like darker blacks and more accurate colors over LCD displays, but are generally not as bright and have their own set of issues.
Plasma displays are made up of many small cells that are filled with gas, typically neon and xenon. High voltage electrical impulses are used to excite this gas, which produces the state called Plasma from which the displays derive their name. As a plasma is produced, it releases electrons that then excite phosphor materials that line the cell, which produce the red, green and blue lights that are used to create an image. Three cells, one for red, green and blue, are grouped together to form a single pixel on the display. By modulating the electrical impulse to produce brighter or dimmer combinations of these three colors Plasma displays can produce any color in the visible spectrum.
Because they lack the backlights that LCD displays use, Plasmas are able to produce much deeper blacks and a higher contrast between the darkest black and brightest white. This also helps them produce more accurate colors. The negative to Plasma displays are that they cannot get as bright as LCD displays, and all of that plasma gas means that the displays can get very hot if they are showing a lot of white. So they don’t melt, most displays turn down the brightness as they show more white (called white falloff). This means that if you are watching TV in a brightly lit room they will be more difficult to view, so if you show a lot of white screens (such as PowerPoint presentations, or documentaries on polar bears), they will look paler than their LCD cousins. Plasma displays are also susceptible to burn-in: if a static image is left on the display for long periods of time, it can result in a “ghost” effect as the burned in image remains visible even after the display has switched to another image. Plasma TVs are much smaller than their rear projection cousins. And because they create the light in the image in the panel itself, they usually have better viewing angles than LCD displays.

LCD Televisions

LCD displays use array of liquid crystal elements to create the image; a backlight creates the light, and the display uses the LCD elements to control how much light passes through tor each the viewer. LCD technology is cheap to manufacture and is relatively energy efficient, making it very popular in HDTVs and other display devices such as computer monitors and cell phone displays. The display passes an electrical signal to each liquid crystal on the LCD display that controls how much light can pass through it, thus controlling the brightness. Each liquid crystal elements can be individually controlled, and color is produced by using filters on the individual liquid crystals. LCD televisions group three elements (for red, green and blue) together to form a singl pixel. By moderating how much light is allowed through each of these three liquid crystals, any one of the pixels can produce any color in the spectrum.
There are various negatives to LCD displays. One of the problems is that it takes a certain amount of time for each individual liquid crystal to change the amount of light that is let through. This can result in ghosting on the display as the crystals lag behind the image, especially in fast action sequences that change quickly. Another problem with LCDs is viewing angle. Each liquid crystal can be thought of as a small pipe that lets light through from the backlight. As the viewer moves off from right in front of the display, less light reaches them. Other technologies, like Plasma, create the light closer to the screen, with the result that the light exits the pipe at a wider angle than an LCD allows.
Another problem is burn-in. If a static image is left on an LCD for an extended period of time, the individual liquid crystal elements may become fatigued and get stuck, ending up with a ghost of that image on the screen. This has become much less of an issue in recent years as manufacturers have used various techniques to address it, such as pixel orbiting. The other problem with LCD displays is the quality of black produced. As the backlight is always on with an LCD display, there will always be some light coming through. Other technologies like Plasma and rear projection displays are able to produce much deeper blacks. LCD’s do have a higher maximum brightness than Plasma displays, however.

1080p Televisions

You probably see the term 1080p thrown around a lot when shopping for HDTVs, along with terms like 1080i and 720p. These refer to the different high defintion signal formats that the display can work with. The quick and easy explanation is that 1080p provides the best quality, so if you’re going to get an HDTV and you want the best picture quality, you’ll want one that supports 1080p. All 1080p displays also support the lower resoltuon 1080i and 720p formats. Most HDTVs of both Plasma and LCD types on sale now are 1080p models, but many rear projection TVs only support 720p or 1080i.
To get a bit more technical 1080p refers to a format for television signals that contains 1080 lines from top to bottom. The “p” indicates that the lines are being dispayed in a progressive manner, meaning that all the lines are being displayed at the same time, 60 times a second. This is in contrast to 1080i displays where there are actually two sets of 540 lines that are alternated very quickly, one set being shown every thirtieth of a second. The result is that 1080i signals look more jittery; imbetween the two sets of frames, the image will have changed, and this produces the odd jagged look of some interlaced TV signals. 720p displays also use progressive scanning, so all the lines are displayed at once, but there are fewer lines to display. Despite the reduced resolution, however, the progressive display can often produce better picture quality than 1080i. For example many sporting events are broadcast in 720p as they contain a lot of motion, and this looks better in 720p.
So once you have a 1080p television you’re golden, right? Not necessarily. The simple truth is that there just isn’t very much 1080p content out there at the moment. Almost all broadcast television is 1080i, and even high definition consumer camcorders only record at 1080i. But there’s still a benefit; a good television will have built in technology to convert a 1080i signal into 1080p by deinterlacing the two sets of lines. You should make sure that your 1080p television is capable of this. Material that is deinterlaced will generally look better than the original 1080i content, but still won’t look as good as a true 1080p signal. In fact about the only place you can get true 1080p content is via a Blu-Ray disc and the now defunct HD-DVD format. Despite the limited availability of content manufacturers are now offering 1080p displays across their entire product range and any potential savings you might have gotten in previous years by going with a 720p or 1080i television are disappearing. We recommend that you do purchase a 1080p television as this will ensure that you get the best picture quality as more and more sources of 1080p content become available.

High Definition Televisions

High Definition (HD) refers to the resolution that a television is able to display. The image on your television is made up of many small dots. Standard Definition, which is the TV that you watched growing up, comes in at a resolution of 480 pixels from top to bottom and 640 pixels from left to right. High definition, as the name suggests, increaess the number of pixels that form the image.
The terms used to describe high definition refer specifically to the number of lines that can be displayed from top to bottom. The different formats of high definition TV signal are known as 720p, 1080i and 1080p. The first refers to content with 720 lines from top to bottom and the latter two to content that has 1080 lines from top to bottom. The “p” and “i” refer to progressive scan and interlaced scan respectively. Progressive scan means that the content is displaying all of the lines at any given moment. Interlaced scan means that content is being alternated between two sets of lines, so a 1080i Tv signal contains the 540 even lines in one frame, and then the 540 odd lines in the next. Progressive scan signals provides higher quality than interlaced scan. In particular the latter can produce a jagged motion and artifacts.
The High Definition standard also defines the aspect ratio of the content. In order to be considered high definition the content must have an aspect ratio of 16:9, which is generally referred to as widescreen content. As such any High Definition content will be widescreen. TV shows filmed in the 4:3 aspect used in standard definition TV can either be stretched to fit the screen, or presented with two black bars on the side to fill out the screen. Currently both content and displays max out at 1080p, however more High Definition standards that have even higher resolutions are being worked on. The next expected resolution of high definition will be 2160p, which has a resolution of 2160 lines from top to bottom and 3840 lines from left to right. The Japanese have also been experimenting with a format called Super Hi-Vision, which has a resolution of 7680 by 4320 pixels. This next iteration of HD is not expected to be commercially available for some years yet.
Another commonly used phrase with HDTVs is Full HD. Although this phrase does not have a formal definition, it usually refers to a display that has enough pixels to represent every pixel of a 1080p signal. The majority of medium and high-end LCD and Plasma HDTVs on the market at the moment are Full HD models, but some rear projection and low-end models claim to be 1080p, but do not have enough pixels to represent every pixel in the signal.

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