The Pros and Cons of LCD TVs 
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Written by Mike Levy   
Wednesday, 01 September 2004


AV Education on RHT

The Pros and Cons of LCD TVs

Written by Michael Levy

Introduction
I remember the first time I saw “2001: A Space Odyssey.” Of all of the wonders predicted in Stanley Kubrick’s masterpiece, I was most taken by the flat screen TV displays. In one scene, the displays are like pads on the table. The LCD monitors that now come with most computers come closest to looking like them. LCD displays have quickly become the reference for personal computing, but they have not expanded in size enough to compete with plasma for home entertainment. While plasma is well ahead in this race, many think LCD displays will be first across the finish line when one format dominates. As the technology advances and LCD conquers its limitations its strengths give it greater viability.


Although both formats are digital, involving direct access of pixels on a flat screen, the similarity ends there. Plasma screens are high voltage devices that create light in three colors (red, green, and blue) in varying shades at each pixel to create an image on the screen. LCD screens filter or block light in three primary colors at each pixel in order to create an image. They need only low voltage to operate, creating much less heat and using much less electricity.

LCD has not grown in size as easily as plasma. At the last CES the largest plasma screen available was 86 inches, while the largest LCD available was 50 inches. The 50-inch LCD had no price on it yet, but promised to be several times the price of a 50-inch plasma. LCD manufacturing costs will have to lower significantly before it will compete with plasma. The questions are, what are the advantages of LCD and what makes it better than plasma?

Large LCD displays were shown at many displays at the last CES, but the display at VOOM, a new HD satellite service, was the most impressive. They seemed to have plastered the walls with them, each playing a different VOOM High Definition channel. In the well-lit environment of the show, the strengths of LCD stood out. The displays were bright, with excellent color definition, and the non-reflective front surface helped picture clarity in the show floor light.

How an LCD Set Works
Like plasma displays, LCD displays replace the cathode ray picture tube in a television with individual pixels that are addressed digitally. Where plasma is a light creator, LCD displays create an image by blocking light. At each pixel, an LCD display has a light source behind two polarized layers. A polarized element allows the light of only one phase through a medium. A liquid crystal is embedded between the two polarized layers. The layers are polarized at right angles to each other, completely blocking light. The liquid crystals between the filters also act as a polarization filter when aligned. The alignment of the liquid crystals is individually controlled at each pixel by transistors. When the transistors are on, they align the liquid crystals to act as a polarizing filter at an angle to the phase of the incoming light. Through a process governed by quantum mechanics, the light is twisted, allowing it to pass through the second polarizing filter. The voltage varies the level of the alignment, and the more the light is twisted, the more light passes through.

The Pros of LCD Displays
Most LCD displays have a non-reflective face. By comparison, the glass surface of plasma screens often reflects the lights in the room, degrading picture quality. Like plasma displays, you can put them almost anywhere. You can hide the connections for power and signal inside the wall, and they use very little space. Like the couple in the famous Phillips ad, you could even put one on the ceiling. Their advantages are that they weigh much less, are far less fragile, and use much less power than plasma displays.

Like plasma displays, if you can put a picture or painting on a specific wall in your home, you can usually put an LCD display there. If you want them to hide away, there are slick new mechanisms from companies like Tech Art that will cover them with high-end artistic reproductions that roll away when you want to watch TV. Other companies like Vantage Point have created hardware called the UFO that allows you to creatively position the thin sets in ways that also allow you to move the set out of the way in a number of innovative configurations. The low power usage and heat generated by an LCD display lowers the need for fans for ventilation and the lower weight allows for a lighter mechanism.

While the plasmas light output degrades with time due to phosphor wear, the LCD does not suffer from the same malady. Like plasma displays, they work in a variety of lighting. They usually have a variety of inputs and accept everything from standard NTSC TV to HD.
Many have DVI inputs as well as composite video, S-video, analog component and RGB. The newest sets even have HDMI digital video connections, the MPAA-approved standard for digitally transmitting encrypted HDTV. The larger sizes are usually true 16x9 HD displays. Many now include upscaling chip sets from Faroudja or Silicon graphics. They process lower-resolution signals like standard DVD or TiVo and convert them to the native resolution of the display. They sense when the incoming source is from a movie or video and process it accordingly, creating cleaner and smoother motion, fewer digital artifacts and better detail.

The Cons of LCD Displays
The black level of an LCD display, while quite good, is not as deep as those from plasma displays or CRT displays because it blocks light rather than creating it. The LCD has a response delay that causes fast motion to blur. Larger sizes are much more expensive than their plasma counterparts and they are not presently available in the largest sizes. Viewing from an angle can be a problem, because the light is coming from behind the pixel through a tunnel. Newer LCD displays are much better at an angle, because the length of the tunnel has been shortened greatly.

How to decide if LCD is right for you?
Consider your usage and the advantages and disadvantages of LCD displays. In choosing consider room lighting, type of viewing, and viewing distance. The viewing distance should be between three and five times the width of the screen for television usage, and no closer than 1.5 times the width for the highest quality sources. Using specifications to choose an LCD display qualitatively is problematic because, as usual, the most important specifications, black level and gray scale definition, are usually left out. The most important factor in moving image quality is not a specification, but the quality of the digital processing, and that can only be judged by viewing a variety of moving images on the screen. Processing quality is very important. Poor processing creates digital artifacts such as blurred images and/or strange dots and lines flashing across the screen.

Remember that the pixel count, maximum brightness and contrast ratio are of secondary importance. If you want the resolution of high definition, it is defined as a minimum pixel count of 720 by 1280. Most units with high definition resolution will look great playing an HD source. The problem occurs when you play a DVD, standard satellite or regular TV source, which is when the quality of the processing becomes most important. Good processing cannot clean up a bad source, but bad processing can create many problems with a clean moving image when scaling up to the panel’s native resolution.
As with plasmas, I would recommend buying a display that has good fundamental parameters and matching it with an external processor. Interlaced film-based material is the hardest to process and benefits the most from a processor. I recommend the processors from Faroudja, Runco, or DVDO. The difference is amazing.

Conclusion
While it seems technology is ever moving forward and quality goes up while the price goes down, it is no reason to deprive your home of the beauty, quality and ease of use of today’s flat panel technologies. You may hear of nanotube technology as the next imaging solution, and it may be the next great flat panel technology, but what you can put in your house right now is a level of image quality previously available to professionals or hobbyists. You will find yourself frequently looking at the picture quality now on your wall in amazement.





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