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Beware fake 120Hz refresh rates on 4K TVs

Many budget 4K Ultra HD TVs claim to have a 120Hz refresh rates. Most are fake. Here’s what you need to know.

23-tcl-6-series-65r617-roku-tv

The TCL 6 series claims a 120 Clear Motion Index. That's not the same as 120Hz.

Sarah Tew/CNET

Think you're getting a 120Hz TV? Hold up just a second. You might not be. 

Many TVs today are 60Hz, despite having "motion rates" and "effective refresh rates" claiming much higher numbers, including 120, 240 and more. TV companies are deliberately hiding the actual refresh rate from you, and it's been going on for years.

In some cases some 60Hz TVs have performance that might be slightly better than a basic 60Hz TV, but lacking the hardware of a true 120Hz TV, they can't offer nearly the same motion performance.

A true 120Hz refresh rate can improve the picture quality a bit by reducing motion blur. It's not a massive factor for most viewers, however, which is why 60Hz TVs like the TCL 6 series and Vizio M series can still rate excellent image quality in CNET reviews. 

On the other hand, true 120Hz makes a TV more expensive to manufacture, so it's rarely found in budget or even midrange TVs. And even higher-end TVs, like Samsung's QLEDs and Vizio's P series, use numbers higher than 120Hz to seem even better with motion.

The weird part is, the way manufacturers are coming up with these fake numbers isn't always total bantha guano. Allow me to explain.

In the US, our electricity is 60Hz, and our TV system is based around that rate. In other areas, it's 50Hz. If you live in Australia or the UK, just read "100Hz" and "50Hz" when you read 120 or 60.

What the hzeck is a Hz?

TV is a series of still images shown fast enough that your brain thinks there's motion. How fast those image are shown -- their frequency -- is measured in hertz (Hz). Matching the 60Hz of our electricity, TVs historically had a 60Hz refresh rate. For this discussion, you can think of 60Hz as 60 frames of video per second.

Nearly all current TV content is 60 frames per second, or far less. Some TV shows are 60 half-frames per second, or essentially 30 frames per second, while nearly all movies are 24 frames per second. Getting different framerates to fit into 60 is a whole other topic, which you can conveniently read about here: 1080i and 1080p are the same resolution

For now the important part to take away is that the stuff you watch matches, or is less than, the 60Hz of a normal TV. Unless you have a computer or an Xbox One, nothing you have will put out more than 60Hz. There are no 120fps movies or TV shows available. Yet.

So if 60 is enough for nearly all modern content, where does 120Hz come from? A 120Hz model creates it, converting the incoming signal to that 120Hz. The main reason is to reduce motion blur. You can read more about the what and why in What is refresh rate?. The short version is that by increasing the number of frames (or another method we'll talk about below), there's a reduction in the apparent blurring of moving objects. You might not have noticed this issue, but many do. It's inherent in all LCD TVs, and LG's version of OLED TVs. 

samsung-motion-rate-240

A typical marketing blurb for refresh rate. Samsung, unlike most other top TV brands, does not list their TV's actual refresh rate, only their "Motion Rate," which is a Samsung-specific term. 

Samsung

Companies use terms like TruMotion (LG), MotionFlow (Sony), Motion Rate (Samsung), Clear Action (Vizio) and Clear Motion Index (TCL) to hint at this aspect of the TVs' performance, but they don't always tell you the actual refresh rate. And that's the problem.

Black frame insertion

One of the most common ways for a manufacturer to bump the refresh rate is using a feature called black frame insertion (BFI). This rapidly turns off an LCD TV's backlight. Or in the case of OLED, turns off the pixels. This means your eye/brain sees an image, then nothing, then an image, then nothing, and so on. 

In theory, this is done fast enough that you can't see it. More advanced versions might "scan" the backlight so only a portion of the screen is dark at a time, though functionally this is the same.

BFI can be quite useful. It's a way to decrease motion blur without resorting to processing tricks like the despised/beloved Soap Opera Effect. If you've ever been to a movie theater that projects film (a rare breed these days), they used this exact technique. A shutter placed between the film and the projection lens, synced to the 24 frames per second of the film, would blank the image on screen while the next film frame slid into position. 

bfi-and-refresh-rate

An illustration of black frame insertion. The original video would have 60 images per second of the friendly fish. A TV with BFI would "insert" 60 black images in between the real images. How long this black image is shown varies depending on the refresh rate of the TV and other factors determined by the TV's designers to create the image they want you to see.

Geoffrey Morrison/CNET

However, BFI is not without its negatives. As you can imagine, "adding" black means the whole image is darker. That in itself isn't a huge deal in today's age of super-bright TVs. Of more concern is the potential for flicker. The TV is now flashing on and off very rapidly, and even if that kind of thing doesn't literally give you seizures, it can be noticeable at best and annoying or fatiguing at worst. It largely depends how a TV implements the BFI, and the TV technology itself. You'll probably be more likely to notice it on a 60Hz TV than on a true 120. That said, at what rate someone sees flicker depends hugely on their brain and the overall light of the room and TV. 

In CNET's TV reviews, for example, reviewer David Katzmaier notices flicker when engaging the BFI modes on many TVs, and he often turns it off -- in effect sacrificing motion resolution to get less flicker and a brighter image. 

And while true 120Hz TV using BFI would perhaps have less flicker, but would probably be called "240Hz" by the company. It isn't, anymore than a 60Hz with BFI is 120. It could be less fatiguing to watch since its flashing would be far beyond most people's flicker fusion threshold.

You can read more about BFI in Black frame insertion: Busting blur from Oculus to LCD TVs.

Processing tricks

Another way to bump up the "motion rate," or whatever a manufacturer is calling their inflated refresh rate number, is by including whatever processing is also going on at the same time. Instead of BFI, a TV can look at two video frames and create an entirely new frame to go in between. This artificial frame has the effect of smoothing out the motion, causing the aforementioned Soap Opera Effect.

So a company with a 120Hz TV might use BFI and claim the TV has a 240Hz "motion rate." On another TV of theirs that is also 120Hz and uses BFI, and also has the fancy Soap Opera Effect motion smoothing, they might claim the TV has a motion rate of 480 or 960? Sound ridiculous? It is. These numbers are largely meaningless.

Sony's MotionFlow XR 1440, for example, has a 120Hz refresh rate. I call them out because the number is huge, but it's worth noting that on their TV's tech spec page, they do list the actual refresh rate. So does LG on its Super UHD TVs. Not all manufactures do.

Since this processing requires a 120Hz TV to begin with (to insert the new frames between the real ones), this is really just an issue about the marketing, not the TV itself. You can nearly always turn off the Soap Opera Effect, if you hate it, or at least dial it down to something you don't mind as much. 

Careful shopping

As with any TV spec, it's buyer beware. When a high-end TV has a popular feature, every company would like their budget TVs to seem like they have the same feature, by any means necessary. If refresh rate is something important to you, and if you hate motion blur, don't take a company's numbers at face value. 

Annoyingly, one company's "240" could be a 120Hz TV, while another company's "240" could be a 60Hz TV. Some companies will loudly promote their artificial TruMotion/MotionFlow/MotionBlahBlah number, but in the spec chart will list the actual refresh rate. Others will only list their "fake" number, requiring you to read TV reviews to determine what's going on.

CNET's TV reviews always list the actual refresh rate, and call out the manufacturer's inflated number as well.

In sum:

  • There are only 60Hz and 120Hz TVs. 
  • There are no 240Hz TVs anymore. 
  • Anything higher than 120 is a fake number. 
  • Since it takes more expensive hardware to increase a TV's true refresh rate, it's rare a budget TV will actually be 120Hz. 

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the sameTV resolutions explainedLED LCD vs. OLED and more. Still have a question? Tweet at him @TechWriterGeoff, then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel and its sequel