High dynamic range, or HDR, is one of the biggest TV buzzwords you’ll come across this year. While 4K (the other big buzzword right now) is about adding more pixels, HDR is about creating better, more dynamic-looking pixels. It does that by boosting contrast and brightness, and providing a wider range of colors than you can get with current 1080p content and displays.

This is the first year that we've seen a large number of TVs with HDR capability. And now that we've had a chance to test dozens of them, it's clear that's there are big differences in HDR performance. That will make it difficult for shoppers to know which TVs can show HDR images in all their natural-looking glory, and which offer only marginal improvements in picture quality.

If you're in the market for a TV with HDR this year, here’s what you need to know.

What Is HDR?

The concept of high dynamic range isn't new. We’ve been talking about it in audio for decades, where it refers to the difference between the softest and loudest sounds in a musical passage. In still cameras, HDR combines the best elements of several photos of the same scene, shot with different exposures. But with TVs, it’s all about improving the contrast between the darker and brighter parts of a scene.

To enjoy an HDR experience, you need content—movies and TV shows—that have been mastered with HDR, plus a display that can reproduce it. Most of the HDR-enabled content right now comes from streaming services such as Amazon and Netflix, as well as from new Ultra HD Blu-ray players and discs. For streaming 4K videos with HDR, you need a relatively fast broadband connection, of at least 18 to 20Mbps. (You can check your broadband speeds at speedtest.net) Ultra HD Blu-ray discs, which have a consistent 100Mbps data rate, provide the best 4K picture quality currently available.

When presented with HDR content, TVs with HDR can display a wider range from black to white, so you can see more details in the very darkest and brightest areas of the picture. You’ll also see “specular highlights,” which are the momentary glints of brightness that appear on illuminated objects, such as the reflections off a car's chrome bumper or a Roman gladiator's armored breast plate. Without HDR, those highlights wouldn't be any brighter than other bright objects in the scene.

To achieve these effects, top-performing TVs with HDR are brighter than regular sets, though HDR isn't just about increasing a TV's overall brightness. Instead, it's about being able to provide the necessary higher levels of peak brightness when the scene calls for it.

Check out the fireworks scene in the photo at the top of the page, for example, which was provided by Dolby to show the difference between high and standard dynamic range. In the standard dynamic range part of the image, on the right, the image seems overwhelmed, with indistinctive masses of brightness and indistinct clouds of smoke. But on the left you can see clearly defined sparks from the fireworks, different colors and intensities in the clouds of smoke, and details in the dark background.

One other thing: Technically it's not part of HDR, but most TVs with HDR also have wider color gamuts, meaning they can display a wider range of colors than regular sets. HDR can give this extended range of colors greater intensity. When done well, TVs with HDR and wider color gamuts offer brighter, more dynamic-looking images with greater contrast, more gradations of colors, and lighting that appears more lifelike. 

Big Differences in HDR Performance

Unfortunately, though, what we've found so far in our labs is that while some HDR-capable TVs produce super-bright, colorful HDR images, others don’t. How can this be? Well, some televisions have the hardware to really take full advantage of HDR. Others can only read the HDR metadata, which is the information embedded in the digital signal that tells the TV how the image should be displayed. These sets, which are being called "HDR-capable" or "HDR-compatible," then try to accommodate the instructions as best they can, based on the TV's capabilities.

Brightness, for example, is a big challenge. Top-performing TVs with HDR can hit anywhere from 500 to 1,000 nits, the unit used to measure brightness. But some so-called "HDR-compatible" TVs can only produce 100 to 300 nits, so they don't have the headroom to produce the peak levels of brightness required for HDR. As a result, we have some TVs in our labs that use the acronym HDR in their packaging, but that don’t look much different from standard dynamic range sets.

There's one other wrinkle: There are actually two types of HDR technology. Fortunately, one of them—called HDR10—has been adopted as a baseline standard, so it’s included in every TV with HDR we’ve seen so far, with the exception of Vizio sets. It's also the only format currently supported by Ultra HD Blu-ray players. The other type is called Dolby Vision, which is positioned as an enhanced version of HDR10. So TVs that support both formats, like those from LG, can use Dolby Vision HDR when that content is available, or HDR10 when the content is in that format. (Vizio has said it will offer a firmware update later this year that will let current models play HDR10 shows.)

Which Models Have Great HDR?

So how can you tell if the TV you’re considering is able to deliver the full HDR experience? It's not going to be easy. To help reduce confusion, the UHD Alliance—a diverse group of TV makers, Hollywood studios, distributors (such as DirecTV and Netflix), and technology companies—has created performance specifications for "Ultra HD Premium" TVs. Sets that pass a certification process can use a new Ultra HD Premium logo on packaging, so you'll know they can deliver top-level UHD (aka 4K) performance in various areas, including HDR.

The problem is that while some brands, including LG and Samsung, have adopted the logo, others, including Sony and Vizio, aren’t submitting their TVs for certification. The same is true for many 4K sets from lesser-known brands that aren't going through the certification process. Until we test them, there's no way to know how well these sets will perform.

That’s why we’re developing more HDR test patterns and utilizing real-world HDR clips that can help demonstrate the differences in performance for those considering one of these sets this year. Right now every TV with HDR capability in our TV Ratings (available to subscribers) has some statement about its HDR performance as part of the set's Detailed Test Results. We're hoping later this year to be able to add some type of HDR score to the TV's evaluations.

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