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What's a scanning backlight?

        Tech | HDTV

A Moving Backlight

Unlike standard backlights, a scanning backlight doesn't stay on all the time. Instead, the light activates when and where it's needed to produce images. By switching on and off very quickly -- hundreds of times per second -- the light can reduce blur and improve contrast at the same time.

Because the light can adjust to the images on the screen, it can shut off when part or all of the screen switches to black. This makes the black images darker and much more distinct versus what you would see on a traditional LCD television. When coupled with an HDTV with a fast refresh rate, you should also notice a reduction in blur.

Scanning backlights have to be ready to turn on and off in an instant. While a traditional backlight may require a couple of seconds to warm up, a scanning backlight doesn't have that luxury. If a scanning backlight can't activate or deactivate within a fraction of a second, the viewer would still see a blurring or fading effect on the screen.

A scanning backlight usually consists of several light sources aimed at specific regions on the back of the television screen. In general, the light sources for a scanning backlight tend to be more expensive than a conventional backlight. As a result, the price of an LCD HDTV with scanning backlight technology may cost more than comparable models that use the traditional backlight.

Not every LCD HDTV uses a scanning backlight. In fact, even in sets that do have one, you may need to adjust your television's settings to activate the feature. Meanwhile, refresh rates continue to climb: Standard-definition television screens refresh 60 times a second, whereas recent HDTV televisions refresh as many as 480 times per second. While television manufacturers claim the higher refresh rates translate into smoother displays of fast action, the individual viewer may have difficulty telling the difference between a high-end model and an ultra-high-end model. Before investing your money in a bleeding-edge television set, you may want to take a careful look to make sure you can actually detect an advantage.

Learn more about HDTVs by following the links on the next page.