Posted by: kookkhu | August 6, 2010

LCD TV Technology

An important first step to choosing between LCD and plasma is to understand the technology. LCDs, or “liquid crystal displays”, produce an image using a technology similar to that in digital wristwatches or pocket calculators. The image only becomes visible when given a light source – LCD TVs therefore have either fluorescent tubes (CCFLs) or light-emitting diodes (LEDs) that shine through the image from behind.

Since, traditionally, this “backlight” shines through the picture constantly, blacks are never truly black – some light always leaks through, making the picture look milky. Newer TVs can dim the backlight in different areas of the screen independently (“Local Dimming”) – using either CCFLs or LEDs – to make blacks deeper and increase the picture’s contrast. Other systems dim the backlight as a whole depending on the picture’s contents – dimmer in dark scenes, brighter in bright scenes. This is known as “dynamic backlight adjustment”. Also, since backlights shine even while the liquid crystals are changing from one image to another, LCDs suffer from blurring that isn’t present in TVs that use other technologies – such as plasma.

Switching the backlight off and on between frames (“pulsing”) can decrease blur. Doing this twice for each frame increases the number of images in a second from 50 (or 60 in the USA) to 100 (120), and is the origin of so-called “100 hertz” technology. Newer such systems actually generate new images based on the existing ones, guessing mathematically where moving objects will be between frames. TVs that do this twice as often again are known as “200 hertz” TVs. LCDs are also well known for having narrow viewing angles – the picture quickly loses contrast and color fidelity as you move to the side of the screen.



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