From pcmag.com ( http://www.pcmag.com/article2/0,2817,2338779,00.asp
):Analysis: Is 240-Hz TV Tech Fake? Some Is
ARTICLE DATE: 01.12.09
By Robert Heron
LAS VEGASOne of the most popular buzzwords among LCD television manufacturers on the 2009 CES show floor was 240-Hz frame rate technology, which means effectively updating the pixels twice as fast as current 120-Hz LCD screens.
The result is increased picture clarity and detail when processing video depicting motion - think panning shots, or the game "Rock Band"'s side-scrolling lyrics.
However, only two LCD manufacturers are delivering true 240-Hz pixel performance. The rest are augmenting current 120-Hz technology with advanced backlight systems that, while improving picture quality beyond the capabilities of 120-Hz display systems, are not technically operating at 240-Hz pixel speeds. Call it pseudo-240-Hz, if you will. And there's a negative, too: one of the byproducts of pseudo-240Hz pixel tricks is a reduction in the overall brightness of the resulting picture.
Samsung and Sony are the only two LCD manufacturers delivering full 240-Hz performance - Sony's currently shipping 52-inch XBR7 and upcoming XBR9 models as well as the 2009 Samsung B8000- and B750-series televisions are delivering full 240-Hz screen refresh rates. The pseudo-240Hz displays from companies such as LG, Toshiba, and Vizio are all using 120-Hz LCD technology with scanning backlight technology, a technique that synchronizes the display's pixel updates to a cycling pattern of illumination generated by fluorescent tube or LED array backlight modules: basically, the two types of backlight systems featured in today's high-performance LCD televisions.
To its credit, Toshiba was very candid about its 240-Hz technology, referring to it in its CES press conference as an "effect". Moreover, a recent press release plainly states that the company's 240-GHz branded televisions use a scanning backlight system paired with a 120-Hz panel.
The main reason why some manufacturers choose to use pseudo-240-Hz LCD technology is simple: cost. True 240-Hz LCD televisions currently require the use of two motion compensation/motion estimation (MCME) chips that help generate the interpolated frames used to enhance low frame rate video - particularly 24p video used to encode most movies - and the related costs are passed along to the consumer.
Sticking with a 120-Hz panel and utilizing such scanning backlight modules enables those manufacturers to keep prices low while improving picture performance. A significant downside to this method of LCD performance enhancement is a 50 percent decrease in overall picture brightness due to the pulsing nature of scanning backlight technology.
I spoke with a Samsung engineer at CES, and he half-wondered that if company engineers added a scanning backlight system to Samsung's current 240-Hz displays, should the marketing department then describe them as using 480-Hz display technology? Why not - bigger numbers are better, no?
Here's the bottom line: while I'm sure the scanning backlight systems will prove to be enhance detail for LCD TVs, (as was the case with Samsung's impressive 120Hz LN55A950, it remains to be seen how close the picture performance of pseudo-240Hz will compare to the real thing.