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The Pros and Cons of LCD TVs
Written by Michael Levy
I remember the first time I saw 2001: A Space Odyssey. Of all of the wonders predicted in Stanley Kubricks 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.