The proliferation and deliberate confusion of terms and technologies has created an almost indecipherable landscape of HDTV of wildly varying qualities and price points. The aim here is to bring some perspective and grounding to the discussion.
When high-definition televisions first became available to consumers, a paradigm shift in viewing quality, and thus television quality, took place. There are a few major factors that govern how good an image looks to the observer of a television, so breaking them down will provide the correct basis for evaluation and comparison.
Simply put, the resolution of the screen is how much virtual space is available on the screen. This is wholly distinct from the physical dimensions of the screen, and has to do only with the digital real-estate in front of you. There are a multitude of different resolutions available on HDTVs and monitors, but there are two main levels to be aware of: 720p and 1080p. The number represents the amount of horizontal digital lines of resolution there are on the screen from top to bottom, and the letter 'p' meaning these lines are displayed parallel to one another. The other letter seen often is the 'i,' as in 1080i. This stands for interlaced, in which the horizontal lines of resolution are displayed overlapping or interlaced with one another. This is generally viewed as an inferior resolution standard and can be subtly noticeable at the 1080 level of resolution. Most people, however, will be hard pressed to see a huge difference between 1080i and 1080p.
This number, represented in cycles per second or Hz, is the number of times the image on the screen can be changed. For LCD TVs, this also represents the speed with which the individual pixels can be switched on or off or have their color changed. The high refresh rate can be best demonstrated when watching live sports or some other quick action, as the motion can frequently look blurry or pixelated at low refresh rates. There's no refresh rate too high, but anything past 60 Hz is testing the human ability to detect, so upwards of 120 Hz or 240 Hz may seem awesome, but most likely will not be actively experienced by the user.
Contrast Ratio / Color Production
Large contrast ratios are bandied about as if seeing only deep blacks and bright whites would be enough for a good viewing experience. The truth is that the color reproduction of a TV set and the contrast ratio need to work together to create a beautiful image. That being said, it is extremely important for the movie-theater feeling that the dark shades be as dark as possible, so a high contrast ratio is a good thing. Anything more that 100,000:1 is good, because it means the brightest white is 100,000 times more luminescent that the darkest dark. Less than that, and the blacks tend to be more dark grey.
As for color production or reproduction (depending on perspective), this has mainly become the purview of the computer chip. Micro-processors handle the complex calculations necessary for displaying the coordinated millions of colors called for by high-definition content.
LED, LCD and Plasma TVs
The best place to start here is to just define everything. LED stands for light emitting diode, which just basically means tiny flashlight. LCD stands for liquid crystal display, which essentially is a very precise fluid version of the lite-brite toys everyone played with ... just a big matrix of color, but one that doesn't produce light on its own. Traditionally, plasma TVs are two thin sheets of perforated glass where the perforations are aligned to create tiny pockets. In these pockets are rare gases, which shine luminously when an electric force is applied to them, thus creating the image.
LCD TVs have used cold-cathode florescent lamps as their back-lighting, and these are the things that made older technology LCD TVs have such poor contrast ratios and burn out so quickly. Today, LCD TVs are starting to use LEDs as their back-lighting, dramatically increasing their lifespan, efficiency, contrast ratios, color reproduction and even refresh rates. Essentially, the LED back-lit LCD TVs are the next generation of flat-panel, but they are not be be-all-end-all. There will come a day soon when fully LED televisions are available; that is, there will be a TV whose light-producing matrix and image and color-producing matrices are all combined into one very flat panel. Theoretically speaking, the display could be no wider than a coin, a dime even!
As for plasma television technology, it's just about the end of the road. Although they enjoyed many years of visual superiority over LCD TVs in terms of color richness and contrast ratio, there's just nowhere for the development of plasma displays to go. Their resolution is fundamentally limited by the size of their gas pockets in the glass, and they will always require back-lighting that will be prone to burning out. Now would be a great time to go pick one up if you're a fan of the technology, so there's always a bright spot.
Hopefully, this guide help put into perspective something that is so simultaneously exciting and frustratingly complicated for the general public to fully grasp. Remember, if it looks good to you, that's the most important determining factor.
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Can I use a monitor as an HDTV? Yes, but you will need to make a few adjustments.