What Your TV’s Refresh Rate Means

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? Not necessarily.  One of the latest techniques is using different technology to approximate the effect of a higher refresh rate, without actually driving the TV at the higher rate.

Confused?  Read on

Refresh Rate
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 highe and include “higher refresh” in lower-priced TVs, the manufacturers have gotten a bit…creative… But rightfully so.

Unlike contrast ratio, fake refresh numbers aren’t complete fabrications. There’s often a fairly simple 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 LCD use backlight or edgelight 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” which will create the dreaded “Soap Opera Effect”.

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.

LG TruMotion

LG isn’t exactly transparent with its TruMotion tech. The description reads: “TruMotion increases the standard 60Hz refresh rate — how often the image is rendered on the TV screen — which drastically reduces blur and yields crisper details. It’s a boon to all fast-action video, but most especially sports, so you won’t miss a thing. LG TruMotion 120Hz, 240Hz, or 480Hz is available on select-model LCD TVs.” Only one TV seems to have TruMotion 480Hz. The rest are TruMotion 240 or TruMotion 120. Their tech specs typically just say “Refresh rate: TruMotion 240Hz.”

Panasonic
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.

Samsung CMR
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, but it doesn’t list the actual refresh of its TVs in the specs section for TVs (only the Clear Motion Rate is listed).

Sharp AquoMotion
“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 honest in its tech specs section:

Refresh panel rate: 240Hz
Refresh scanning rate: AquoMotion 960

and

Refresh panel rate: 240Hz
Refresh scanning rate: AquoMotion 480

the problem is that you can’t turn on the backlight scanning without turning on the frame interpolation circuitry.

Sony MotionFlow
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.”

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.

just like Panasonic and LG, you can choose to use the frame interpolation or the backlight blanking, or both.

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.”

Although Toshiba never actually admit it, based on my talks with toshiba engineers at CES, they use backlight blinking to achieve those numbers.  Kudos to Toshiba, however, for being the inly company that uses the proper way of reducing motion blur by only using blinking instead of frame interpolation.

Bottom line?
Backlight blinking and/or scanning = good, frame interpolation… Not so much!