Common Problems for LCD TVs
LCD TVs are quickly gaining momentum in the flat panel HDTV market. Their low power consumption and lightweight design add to the general attractiveness of an LCD panel television. They also boast an ultrabright screen with images that seem to "pop" out on the showroom floor. While LCD TVs are a fantastic solution, the technology is not perfect. When buying a new flat panel HDTV, consider the common problems found in LCD televisions in contrast with competing flat panel technologies.
Older LCD televisions suffered from an imperfection known as "Ghosting." Ghosting is described as a trail following objects in motion on the screen giving a streaked effect. This is caused by a slow response time in the pixels themselves. Response time was formerly known as the amount of time it takes for a pixel on a LCD to switch from white to black. Because a pixel is rarely completely off, LCD manufacturers measure the time it takes a pixel to go from gray to gray to more accurately standardize response time rates. Response time is measured in milliseconds.
Refresh rate is measured in Hertz. This is simply how many times per second an image is refreshed on the display. In the United States, LCD televisions have a refresh rate of 60Hz according to the NTSC standard.
3:2 Pulldown and Higher Refesh Rate
Movies and film are recorded at 24 frames per second. Output devices such as camcorders, DVD and Blu-Ray players send the 24 fps signal to the display, which refreshes the screen at a rate of 60 Hz. To fit 24 fps into 60 Hz, a method known as 3:2 pulldown is used. This displays the first frame two times and the second frame three times and repeats the process for five frames and starts over. This method causes an effect known as "Judder." Fast motion and camera panning look shaky when 3:2 pulldown is implemented. To accommodate, LCD manufacturers have released LCD TVs with a refresh rate of 120 HZ and even 240 Hz, both of which are multiples of 24. Due to the high refresh rates, additional frames are interpolated as to further smooth out the pulldown effects. While higher refresh rates do reduce judder, motion often looks artificial because of the interpolated frames.
LCD panel technology uses backlighting to control the brightness and contrast. Light seepage from the backlighting causes dull picture quality and gray or even blue blacks. Contrast ratio is how many of shades of grey in between white and black on an LCD panel.
The Contrast Ratio Dilema
Contrast ratio, however, is not a standardized measurement, and LCD manufacturer's test contrast ratio according to their own methods. Therefore, judging contrast ratio by the number printed on the HDTV is completely inaccurate.An LCD with a good contrast ratio will display inky blacks while retaining details in dark scenes without seepage from the backlighting. Because the pixels in a plasma screen television are lit individually, the contrast ratios are much better.