Just because your TV says it has a refresh rate of 120Hz or 240Hz, does that mean it's actually refreshing at 120Hz or 240Hz? Nope, not necessarily. One of the latest marketing techniques, shall we say "gifts for fiction," is using different technology to approximate the effect of a higher refresh rate, without actually driving the TV at the higher rate.
Confused? Yep, that's the point. Hopefully I can deconfusify you.
OK, first the basics. Refresh rate is how often a TV "refreshes" or changes the image on screen. In a way, this is like the TV's "frame rate," though functionally the two are bit different. A TV with a 60Hz refresh rate creates 60 individual images on screen each second. With the current HDTV system, this is the maximum you can get from any source.
The problem is, all LCDs suffer from motion blur, where the image blurs or "smears" with any motion. One way to combat this is with a higher refresh rate.
The problem is, it's more expensive to make an LCD that refreshes at a higher rate, and "120Hz" and "240Hz" have been marketing gold for the TV manufacturers. So in an effort to drive the numbers ever higher (my 960 is better than your 480!) and include "higher refresh" in lower-priced TVs, the manufacturers have gotten a bit...creative.
Unlike contrast ratio, fake refresh numbers aren't complete fabrications. There's often a fairly simple (if logically dubious) method for determining each company's refresh rate claims. There are two primary methods for boosting the numbers, beyond actually using a faster refresh panel.
The first is a scanning or flashing backlight. All LCDs have a backlight to create the light used by the liquid crystal to create an image. Typically this is always on, or at least cycling at the same 60Hz the rest of the TV runs at. If the TV instead flashes this backlight rapidly, your eye would see the image, a moment of black, then the image again. It does this so fast, you don't see the flicker. Technically, you're seeing each frame of the image twice per second. This is a common practice, and can reduce motion blur. The issue is calling it "120Hz" when it's really just a 60Hz TV with a scanning backlight causing you to see the same frame twice in a row.
Another method for potentially reducing motion blur slightly, but increasing the claimed refresh rate a lot, is video processing. Often this is "motion smoothing."
Because so many TVs are marketed with a combination of the above either in addition to, or instead of, actually increasing the refresh rate, manufacturers don't want you to know what the actual refresh is. So here's what a few of them call their higher refresh tech, and what it really means. (It's worth pointing out that every TV we review here at CNET lists the actual refresh rate in the Features section of the written review).
The one LG LED LCD we've reviewed so far this year, the 60LA8600, is listed by LG as "TruMotion (frame rate): 240Hz," and we found out from LG that it is a 240Hz refresh panel. On the other hand, last year's 55LM6700 had a claimed "240Hz effect" but actually had worse motion resolution than some 120Hz TVs. So don't assume their numbers describe the panel refresh.
Panasonic is upfront about its backlight scanning: "120Hz, 1,200 Backlight Scanning Technology. Our advanced 1,200 Backlight Scanning technology employs fine light-emission control to minimize flicker and ensure smooth images without afterimage effects, even during high-speed action scenes in movies or sports programming." There's even an image to show what's going on:
There's also "120Hz, 240 Backlight Blinking Technology. Panasonic's 120Hz/240 Backlight Blinking Technology delivers optimal sharpness, clarity, and contrast with virtually no image blur."
There are a few other variations like this. The gray bar in the illustration is a darkened row of LEDs that scans vertically.
Though Samsung is fantastic at creative marketing ("LED" TV was its thing), it at least doesn't outright call the TVs with the aforementioned tricks "480Hz" refresh. Instead, it has "CMR" or Clear Motion Rate. "Samsung's more comprehensive Clear Motion Rate takes into account all three factors that contribute to motion clarity: panel refresh rate, image processor speed, and backlight technology." In other words, a TV with a CMR of 240 could be a 120Hz panel, with an average processor, and a scanning backlight, or a 60Hz panel, a fancy processor, and a scanning backlight. It's unlikely a TV with a CMR of 240 would be a 240Hz panel, as such an expensive panel would almost certainly come with one or both the other features. Here's an illustration showing how it gets the numbers.
Samsung links to this article to explain CMR, which is great (there's this one, too), but it doesn't list the actual refresh of its TVs in the specs section for TVs (only the Clear Motion Rate is listed).
"AquoMotion 960, Sharp's backlight scanning technology, quadruples the effective refresh rate to hit you with all the power that fast-moving sports and movies can deliver." Even I can do that math 960/4=purple. No wait, 240. That's for its 8 series. For the 7 series: "AquoMotion 480, Sharp's backlight scanning technology, doubles the effective refresh rate..."
The company is also, ahem, refreshingly honest in its tech specs section:
Refresh panel rate: 240Hz
Refresh scanning rate: AquoMotion 960
Refresh panel rate: 240Hz
Refresh scanning rate: AquoMotion 480
Sony gets a bit of an eyeroll for this one: "Motionflow XR 960 helps you see each end-over-end rotation [of the ball] by taking motion clarity beyond refresh rates, which are only measured in Hz, to quadruple the motion effect so you see everything as if you were there."
Emphasis, mine. However, it does list in the product description "240Hz refresh rate" separate from the MotionFlow rating.
Here are two images pulled from Sony's Asia site. These TVs are for 50Hz electricity (the U.S. is 60), so the versions of TVs it gets are multiples of 50, whereas ours are multiples of 60. Same concept, though. Here's MotionFlow 800 (our 960):
And 200 (our 240):
The text is a little hard to read, but the gist of it is MotionFlow is a combination of frame interpolation and backlight scanning.
Toshiba ClearScan and ClearFrame
Toshiba, like some of the other companies here, doesn't go into detail about its ClearScan and ClearFrame tech. "Toshiba ClearFrame 120Hz doubles normal 60Hz performance to reduce blurring caused by fast-action video. And our ClearScan 240Hz goes a step beyond, quadrupling the 60Hz rate to create a 240Hz effect. They both improve picture clarity dramatically, without impacting brightness or adding flicker. And for those who prefer a more film-like picture, ClearScan 240Hz also offers a 5:5 pull-down option."
Since the one ClearScan 120Hz TV we've reviewed of Toshiba's this year was most definitely a 60Hz LCD, it's, ahem, clear the company is taking liberties in what "120Hz" actually means.
"SPS (Scenes Per Second) combines advanced 120Hz technology with scanning backlight for enhanced detail." In other words, a "240Hz SPS" is a 120Hz TV with a scanning backlight. On the Web site, the company says things like "240Hz Effective Refresh Rate," "120Hz Effective Refresh Rate," and "Enhanced with smooth motion and backlight scanning for amazing sharpness," so it's being fairly upfront about what's going on...sort of. Here's what David found out with this year's E420i-A1: "Vizio actually uses the term '120Hz effective refresh rate' on this and other TVs, including the E601i-A3. But while that set has the smoothing and motion resolution we expect from a 120Hz TV, the E0i-A1 series has neither. That's why we're sticking with the '60Hz' specification on the table above, despite what Vizio says." In other words, Vizio has two TVs, both labeled with "120Hz effective refresh rate," but one is a 60Hz panel with backlight scanning and the other is a true 120Hz panel.
Plasma TVs don't have higher refresh rates in the same sense that LCDs do. Instead, you'll often see claims of "600Hz" and more. This isn't directly comparable 120Hz or 240Hz. For more on that, check out "What is 600Hz?"
For the TVs CNET reviews, we'll list the actual refresh rate. For other TVs (sorry, even we can't review them all), some manufacturers at least list what the panel refresh actually is.
Just because a TV claims a certain refresh rate, don't assume it's actually that refresh. True, the methods typically used to justify inflated refresh rate claims can help motion blur, it isn't the same as actually increasing the refresh rate.
As a last resort, if you can't find the info anywhere, if a TV lists a higher-than-60 refresh rate AND has motion smoothing/motion interpolation, chances are it's a 120Hz panel or higher. If it doesn't have that extra processing, it's likely a 60Hz panel, with black frame insertion (if that).
Got a question for Geoff? First, check out all the other articles he's written on topics like HDMI cables, LED LCD vs. plasma, active vs. passive 3D, and more. Still have a question? Send him an e-mail! He won't tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter @TechWriterGeoff or Google+.