CNET también está disponible en español.

Ir a español

Don't show this again


The truth about Ultra HD 4K TV refresh rates

Today's Ultra HD 4K TVs are all marketed with "motion," "action" and "clear" numbers that start at 240Hz and go up from there. They're all basically made up. Here's the real story.

Even high-end 4K TVs, like this Samsung JS8500, have a true refresh rate of at most 120Hz. Sarah Tew/CNET

There's a simple rule of thumb for companies that market electronics: When it comes to specs, a higher number is usually preferred. Sure, there are exceptions -- you want things like response time, load times and mobile device weight to be low -- but generally, more equals better. It comes down to the "speeds and feeds" aspect that still dominates a lot of tech shopping: When you line up a bunch of similar TVs, phones, laptops or tablets, the ones with the higher numbers get the edge. Think about battery life, display resolution, screen size, processor speed, memory and storage capacity, to name just a few.

Of course, the quoted number is often only half the story. Consider the megapixel myth of digital cameras: a 15-megapixel camera isn't necessarily going to yield a "better" picture than an 8-megapixel shooter. Nor is a 4K Ultra HD TV -- with a resolution of 3,840x2,160 pixels -- going to necessarily outshine a "standard" HDTV with 1,920x1,080 pixels, or just one-fourth of the 4K screen's resolution. Plenty of other factors, including color accuracy and contrast ratio (not to mention the quality of the video source) will affect the picture quality to a normal eye.

Then there's refresh rate. This spec refers to the number of times per second that a video screen is updated, with a higher number yielding a smoother, more natural-looking motion (up to a point). The baseline for this number was set back in the last century, with movie projectors hitting 24 frames per second (expressed as a frequency in Hertz, or Hz), and old standard-definition TVs set at 60Hz in the US or 50Hz in many other countries.

In the HD era, though, TV manufacturers started an arms race of sorts, ramping up refresh rates in increasing multiples to 120Hz, and even eventually 240Hz. There was even a time where some plasma TVs were claiming, somewhat dubiously, a 600Hz refresh rate of sorts: the "more equals better" situation again.

So, now that we're in the post-HD 4K TV era, we're clearly up to 480Hz, right? Or possibly 960Hz?

Not exactly. The fact is that nearly all of these new 4K TVs -- which now make up the increasing majority of all TVs priced over $1,000 in the US -- have, at best, a 120Hz refresh rate. Actually, many of the least expensive 4K sets are 60Hz, and none that we know about are 240Hz.

You may be asking yourself, what's with all the 4K TV marketing that claims numbers of 240 or even higher? Well, they're fluff. Very carefully worded marketing fluff, in most cases.

But does that mean those of you trading in a recent 240Hz 1080p TV for a bigger, sub-240Hz 4K Ultra HD TV are actually downgrading your picture quality?

The answer, as always, isn't so cut and dry.

Now Playing: Watch this: Samsung shows off latest curved screen, ultra-HD TV

What's refresh rate?

To recap: Refresh rate is how often a TV changes the image (also known as a "frame") on screen. With traditional televisions, this was 60 times each second, or "60Hz."

Some modern TVs can refresh at much higher rates, most commonly 120Hz (120 frames per second) and 240Hz. We've covered this before, with 1080p HDTVs, but it's the same idea.

But is this just yet another "more is better!" marketing ploy? Do the bigger numbers matter? Actually, they can: Higher refresh rates on LCDs and OLED TVs -- which, post-plasma, are pretty much the only two mainstream TV technologies left -- can help decrease motion blur.

What's motion blur? Glad you asked...

Your brain on blur

All LCD and current OLED models suffer from "motion blur." This is where anything in motion, either an object moving on screen or the entire image (like when the camera pans), blurs and looks softer than if it was stationary.

Geoffrey Morrison/CNET

Interestingly, this blur is largely created by your brain. Basically, your brain notices the motion, and makes assumptions as to where that object (or overall image) is going to be in the next fraction of a second. The problem with LCD and current OLED TVs is that they hold that image there for the full 60th of a second, so your brain actually smears the motion, thinking it should be moving, when in fact it's just a series of still images.

It's actually quite fascinating, but the details are beyond the scope of this article. I recommend checking out BlurBuster's great article for more info.

The motion blur we're talking about here is caused by the television, on top of whatever blur the camera itself creates. Some people aren't bothered by motion blur. Some don't even notice it. Others, like me, do notice it and are bothered by it.

Refresh rate and beyond

Refresh rate itself is really only part of the solution. Just doubling (or quadrupling) the same frames doesn't actually do much for reducing motion blur. Something else is needed.

There are two main methods. The first is frame interpolation, where the TV itself creates brand new frames that are sort of hybrids of the frame that came before, and the one that comes after. This can fool your brain enough that it doesn't blur the image. Depending how aggressive the interpolation is, however, it can lead to the soap opera effect, which makes movies look like ultra-smooth reality TV. Some viewers like the effect, but it's generally hated by film buffs and others who pay close attention to image quality.

The other is black frame insertion (BFI), or a scanning backlight. This is where all or part of the backlight of the TV turns off (goes black). This effectively means the image doesn't "hold" in place, so your brain doesn't blur it. Do it poorly, however, and many people will see the image flicker. The light output of the TV also drops as it's basically not outputting any light much of the time.

Why 240Hz matters

At a minimum, to do motion interpolation or black frame insertion, you need 120Hz. Trying to do this with a 60Hz TV means with a lot of content, the TV would be throwing away information. Also, the backlight flashing would be visible to most people.

240Hz is better, as you can flash the backlight much faster (so it's less noticeable), and you can have more finesse with how you create the new frames (given that you have three new frames to create, as opposed to just one with 120Hz).

But at the very least, you need 120Hz to really combat motion blur, which is good, because right now, that's the most you can get with a 4K TV. All 4K TVs on the market today (as of this writing), are 60Hz or 120Hz.

If that's surprising to you, and it likely is if you've shopped for a 4K TV, it's because many manufacturers are being, shall we say, "creative" with their refresh rate claims (well, still being creative, this was and is common with 1080p TVs too).

Sarah Tew / CNET

Ah, marketing

Misleading specifications are a fact of life in the tech world, but that doesn't make them OK. Refresh rate is a real, measurable thing. If a company says "120Hz" refresh, there's an expectation in my (and I assume, your) mind that the TV shows 120 different images per second. Or at least, is capable of that. If it doesn't, if it's a 60Hz TV with black frame insertion for example, it may have similar motion resolution to some true 120Hz TVs, but it's not actually 120Hz.

So many (most?) of the refresh claims you see on 4K TVs are likely somewhat misleading. None are more than 120Hz, despite what their numbers claim, and many are just 60Hz.

Here's the best way to read refresh specs: If it uses any sort of modifier ("TruMotion 240Hz"), or doesn't explicitly say it's the panel refresh, it's probably not. The few companies that disclose the actual panel refresh information on their websites are quite clear what the panel is doing, and what the backlight and processing assistance does.

Here's a look at each major TV maker's current motion-related marketing.

Actual refresh rates of 2015 TVs

Brand Model Claimed Actual
LG UF7600 TruMotion 120 60Hz
All other 4K TVs TruMotion 240 120Hz
Panasonic CX600 Image Motion 120Hz 60Hz
CX650/CX800 Image Motion 240Hz 120Hz
CX850 2400 BLS 4K IFC PRO 120Hz
Sharp All models - As listed
Samsung All models - Half listed motion rate
Sony All 4K models - 120Hz
Vizio Most E-series - 60Hz
E65-C3, E70-C3 120Hz
M-series - 60Hz
M-series >/=60in - 120Hz

LG: TruMotion

LG, like several other brands, uses "Hz" but qualifies it with "TruMotion," which it describes as: "TruMotion reflects the benefits of our detailed backlight scanning and enhanced frame rates to reduce blur and yields (sic) crisper details."

So it's all the methods above. It doesn't list just the panel framerate in Hertz anywhere, unfortunately.

So we asked. According to LG, the UF7600 is natively 60Hz, while the UF7700, UF8500, UF9500 are all 120Hz.

Panasonic: Image Motion or Backlight Scanning

Most of Panasonic's models feature some kind of BFI or scanning, but its top 4K models are listed in the specs as actually having 240Hz refresh. Elsewhere, however, it describes it thus: "Image Motion Technology uses high quality frame creation and advanced back light scanning to ensure fast action scenes are always clear."

Panasonic has updated its website to list accurate refresh rates, and confirmed to us the CX600 series has a 60Hz refresh, while the CX650, CX800, CX850 series have 120Hz.

Sharp: AquoMotion

Sharp gets multiple bonus points here for listing the "AquoMotion" rate, and the panel's native refresh and clearly describes how it works: "AquoMotion, Sharp's backlight scanning technology, multiplies the effective refresh rate to hit you with all the power that fast-moving sports and movies can deliver."

Most of its 4K models are 120Hz natively, whereas some of the smaller and less expensive models are 60Hz.

Samsung: Motion Rate

Samsung is more upfront than it used to be about this. Its 4K TVs feature "Motion Rate 240" (notice the lack of "Hz") which it describes thus: "Enjoy our best moving picture resolution at Motion Rate 240 with exceptional refresh rate, processing speed and backlight technology." Here's a diagram:


As it explains, "Clear Motion Rate is a motion clarity standard put forth by Samsung Televisions in order to replace what is commonly known as the 'refresh rate' associated with many televisions." It includes motion processing and backlight scanning into one number that might allow you to compare Samsung models with each other, but is meaningless compared to other TVs.

As far as Motion Rate 240 goes with its current 4K TVs, it's a 120Hz refresh rate panel with some sort of backlight scanning or BFI.

Sony: MotionFlow

According to Sony, all its 4K TVs are natively 120Hz. Its specification sheets mention a high number and "MotionFlow XR" which uses a combination of the techniques above.

Vizio: Clear Action and Effective Refresh Rate

Vizio seems like it's listing the actual refresh rate of its TVs, but at least it labels it as an "Effective" refresh rate. Meaning, it's like that rate, but not. We asked Vizio for an explanation and learned that most of its 2015 E series TVs have 60Hz refresh rate panels, while in the 2015 M series only the 60-inch and larger TVs have 120Hz panels (the smaller ones are 60Hz).

Bottom line (should you care?)

There are two things at play here. The first is simple, and one we've said many times before: don't trust marketing. At least, don't trust it at face value. Marketing is designed to sell you a product, not give you information about a product. That's secondary.

The second is being able to reduce motion blur. When 120Hz 1080p TVs first hit the market, they offered a noticeable improvement in motion resolution. The technology has only gotten better. When 240Hz TVs hit the market, I and many other reviewers felt they offered a slight but not substantial improvement over 120Hz models. So is it a big deal that there are no true 240Hz LCD TVs? No. Would a 240Hz 4K TV look more detailed than a 120Hz model? Maybe. It depends how it did the other processing and backlight manipulation. Will we see 240Hz 4K models? Probably.

So if you're sensitive to motion blur, it's worth checking for a 120Hz model. It would be a shame to let all that extra resolution go to waste. It's also worth checking reviews for subjective takes on how the TV handles motion -- that's more useful than any manufacturer-supplied spec.

Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED, why 4K TVs aren't worth it 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 sci-fi novel and its sequel.