Two of the most confusing letters thrown around in reference to LCD and TVs these days are "H" and "z." The confusion will just continue to mount this year, as numerous manufacturers announced 240Hz displays at CES, doubling the 120Hz spec in an attempt to lure buyers. But is it twice as nice?
Until proven otherwise, I'm saying no, 240Hz is not worth waiting for.
Before I get into why, it's probably worth writing a few sentences to sketch out what all these numbers mean. Standard LCD and plasma TVs refresh the screen 60 times per second, or 60Hz, which is plenty fast enough to eliminate flicker and create the illusion of motion from a series of still images. In fact, most sources sent to your display arrive at the nominal rate of 30 frames per second, and each frame is repeated once by the television to achieve 60 total fps.
The problem is that with LCD, some viewers can perceive motion blur in fast-moving objects on standard 60Hz models (motion blur like this isn't an issue with plasma or other display types, whether 60Hz or otherwise, because they use different methods to create the illusion of motion). To reduce blurring, most 120Hz LCD displays use interpolation--called MEMC for "motion estimation-motion compensation"--to create a new frame between each of the original frames, so there's one interpolated frame for every true frame. An interpolated frame is composed of the processor's best guess as to what should be there, based on the contents of each of the true frames.
At CES, LCD TV makers announced new models with 240Hz refresh rates, which are designed to reduce motion blur even further. There are two distinct methods used by different manufacturers to arrive at that number. I've reviewed one 240Hz display, the Sony KDL-52XBR7, which uses MEMC again to basically double the 120Hz process described above--so for each "true" frame there are three interpolated frames. Samsung also uses MEMC to get to 240Hz.
LG, Toshiba, and Vizio, on the other hand, use what's called "scanning backlight" technology. Instead of interpolating a second time, it uses MEMC once to get to 120Hz, in combination with a backlight that flashes on and off very quickly, to claim a 240Hz refresh rate. Notably, Toshiba used the careful phrase "240Hz effect" at its press conference to describe the scanning backlight method, although we doubt the distinction will filter down to the product packaging. I haven't reviewed any displays that use this method yet, so I can't speak to whether one method is better than the other.
Despite having reviewed only one HDTV with 240Hz, however, I'm fairly confident that the feature, regardless of how it's implemented, is not worth waiting for on its own, unless you're the kind of highly sensitive viewer who already perceives motion blur in 120Hz models.
Personally, I have a difficult time perceiving motion blur in standard 60Hz LCDs, even in side-by-side comparisons with 120Hz LCDs or plasmas, unless I'm using specialized test material. (I'm talking about motion blur only here, not "smooth" dejudder processing, which is separate from refresh rate and quite easy to perceive.)
According to that test material, the 240Hz Sony XBR7 did in fact reduce motion blur significantly compared with 120Hz displays, so I'm willing to believe claims that 240Hz is less-blurry than 120Hz. In case you're wondering, the XBR7 delivered between 900 and 1,000 lines of motion resolution, which matches the result of a typical plasma.
That compares with 500-600 lines for a standard 120Hz model like the Sony KDL-52XBR6 and 300-400 lines for a 60Hz LCD. But those results were with test patterns. The real question is whether you actually tell the difference in everyday viewing? For most viewers, the answer is "no."
Hey, maybe I'll be surprised when I do get my hands on more 240Hz TVs and they turn out to be the cat's meow. Anything can happen, but until then I'm not telling anyone to hold out for 240Hz tomorrow when you can get 120Hz (or less!) today.