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Panasonic TC-55CX850U 4K LED TV Review

55 in.

This TV is both subtle and accurate, but we're not sure who its audience is.

Credit: / Lee Neikirk
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Last year, Panasonic's flagship AX900 blew us away, offering picture quality nearly on par with the company's storied plasma sets. Unfortunately, it was out of reach of most buyers, retailing for around $8,000—assuming you could even find it.

This year, Panasonic aims to make that quality more affordable than ever. The Panasonic TC-55CX850U (MSRP $3,499, online for $2,499) may not be quite as fancy as the AX900, but it still checks off a lot of our favorite boxes: full-array backlighting with local dimming zones, wide color support, apps with 4K streaming, professional tuning controls, a high-quality metal finish, and HDR support.

For the price—$2,500 for the 55-inch or $3,500 for the 65-inch, right now—the CX850 is a little pricy, but is a very rewarding 4K option given the right viewing conditions. While the dimming function likely won't satisfy consumers shopping for a strict home theater, this TV is an excellent choice for viewers who watch with a few more lights on, and are hunting for a TV that treats both 1080p and 4K content with the utmost care and respect.

Series Information

The CX850U series keeps it simple

Panasonic's CX850U 4K TV series is available in a 55-inch and a 65-inch screen size. The exact model names are Panasonic TC-55CX850U and Panasonic TC-65CX850U. Since their release, pricing has dropped for both TVs from the original MSRP: the 55-inch started at $3,499 but is available for $2,499, and the 65-inch started at $4,499 but is available for $3,499.

Both are 4K LED sets with full-array backlighting and local dimming, and compatible with Panasonic's new smart platform based on Firefox OS. The CX850 TVs are also HDR (High Dynamic Range) compatible and cover 98%/90% of the DCI-P3 color gamut for the 65/55-inch respectively. Connectivity options and accessories are identical between models.

Our 55-inch CX850U was received on loan from Panasonic, but was not new out of the box and had a few days under its belt already. We gave it another 24 hours of break-in time and performed a factory reset prior to testing and evaluation.


This is no plastic fantastic

The CX850 might not fetch the same premium price as Panasonic's 2014 flagship, but it's still built to very high standards. Smooth metal bezels run the perimeter of a screen that perches upon a slim metal stand. Like Panasonic's late-great plasmas, the CX850U is quite heavy—but it's durable and clearly built to last.

Credit: / Lee Neikirk

The CX850 sports a clean, minimalist design that boasts a sturdy form-factor thanks to its metallic bezels and stand.

The view from the front is all screen, with connectivity and control buttons hidden away on the rear casing. Around back, you get three HDMI ports (HDMI 2.0/HDCP 2.2 compliant), three USB inputs (one USB 3.0, two USB 2.0), shared component/composite inputs, a coaxial jack for cable/antenna, and digital (optical) audio output. There's also an SD card slot and ethernet (LAN) hookup.

Credit: / Lee Neikirk

The standard remote is durable and generous with buttons, providing ample surface area and lots of useful hotkeys.

Included with this TV is a standard Panasonic infrared remote, dressed in matching silver tones. Like the TV, it's on the hefty side, allowing ample space for large buttons and big navigational keys.

Highlights include a dedicated Netflix button, a full number pad, big channel/volume rockers, and a backlight that bathes each key in a spooky red glow.

There's supposed to be a smaller touchpad remote too, but our unit didn't include one. I've used the remote before, however, and can attest to how much better it is for typing and browsing websites than standard remotes.

When it comes to day-to-day use I still reach for the traditional clicker for most tasks, but the touchpad is superior when it comes to the smart features you'll find in Firefox OS.

Firefox OS

An uncomplicated smart TV experience? Just what the doctor ordered.

I first scoped out Panasonic's new smart platform, "Firefox OS," while reviewing the company's CX800 4K TV earlier this year. I initially had mixed feelings, as the naming led me to believe that it would integrate some of the titular browser's features—like Google TV did once upon a time. Unfortunately, it's "Firefox" in name only.

But even though there's no real parity between Firefox OS and the PC browser, taken simply as a smart TV experience it's comfortably streamlined and easy to use. While not as highly tooled as Samsung's Tizen OS, Firefox OS does manage to successfully ape the clean feel and slick presentation of LG's webOS platform—to an extent.

Credit: / Lee Neikirk

The main gist of Firefox OS includes three sub-menus: LiveTV, Apps, and Devices.

Firefox OS exists in three sub-menus: Live TV, Apps, and Devices. Live TV is exactly what it sounds like, but it's also kind of a strange choice as a primary menu. While the TV can integrate your programming with zip code and provider information, the Live TV widget simply brings you to the coaxial input by default. If you, like most people, hook up your cable box via HDMI, you won't get to it with this option.

The "Apps" section is also exactly what it sounds like. Here, you'll find a few 4K-capable options like Netflix, Amazon Instant, and YouTube, as well as some other popular partners like VUDU. Panasonic has an App Market, too, but the apps that are already installed are the ones you'll want.

Credit: / Lee Neikirk

We imagine most users will jump right into the Apps menu, and get to the best smart options like Netflix and YouTube, both equipped for 4K streaming.

Last but not least, Devices is simply a way to connect to your own media—such as photos, videos, or music files—via USB, DLNA, or one of Panasonic's proprietary mobile apps.

In addition to these options, there's also a built-in browser. As usual, it pales next to traditional non-TV browsing methods, but still works much better than Panasonic's previous iterations. It's not something you'll use often, but pages load quickly enough, and it's easy to star and favorite websites you visit frequently. Navigation and typing with the standard remote isn't ideal, but the touchpad remote makes browsing much easier.

Credit: / Lee Neikirk

The browser works great with the included TouchPad remote, but it's still a far-cry from the smoothness of a PC, tablet, or smartphone.


More picture modes than you can shake a remote at.

Where Firefox OS is minimalist and simple, the TV's actual menu software is anything but. Panasonic tends to pack their consumer displays with oodles of customization options, with an aim to appeal to the most invested videophiles and TV calibration enthusiasts.

To wit, the CX850U features nine different picture modes, each tailored for a slightly different optimal use case. And you thought your iPhone was complicated!

Credit: / Lee Neikirk

The CX850U features a huge variety of picture modes, which is especially appealing to videophiles and enthusiasts who may prefer a different mode/calibration for each source device.

The first three modes—Vivid, Standard, and Home Theater—offer the usual retail store/energy star/living room setup that every TV ships with nowadays. On top of that, you also get THX Cinema, THX Bright Room, Cinema, Custom, Professional1, and Professional2 modes.

This is a direct appeal to the videophile crowd, where a mode for each use-case is much more preferable than a one-size-fits-all scenario. For example, you might want to use THX Cinema to watch 4K footage off of Netflix and THX Bright Room on sunny days, while saving Custom for a PC input and one of the Professional modes for filmic content.

Credit: / Lee Neikirk

The CX850U features a huge variety of picture customization options, including 2/10 point white balance, a full (and functional) CMS, and a 10-point gamma luminance slider.

Viewers should at least considering setting up Professional1 and Professional2 as day/night modes. Those modes give users access to all the basic controls, as well as more advanced options for white balance and color tuning. And, as usual, there's full 10-point gamma control here, enabling you to tighten the CX850U's picture to professional display levels.

And it wouldn't be a high-end TV without a laundry list of software enhancements and automated backlight controls. In the advanced and pro menus, you'll find toggles for things like adaptive backlight, motion enhancement, game mode, vivid (expanded) color, color remastering, video/MPEG noise reduction, and 3D settings.

Credit: / Lee Neikirk

Fans of big audio will want to pair a soundbar or surround sound system with the TV, but the built-in speaker controls should satisfy more casual listeners.

Picture Quality

A kingly picture—without the pomp and circumstance.

Like Panasonic's own AX900U, Sony's X950B, and Vizio's M Series, the CX850U has what's called a full-array backlight with local dimming. This means there are LEDs behind the entire screen rather than along the edges.

These LEDs dim and boost dynamically, making for better black levels and greater screen uniformity. This backlight design also makes it possible for the CX850U to play High Dynamic Range content, though that functionality won't be available until Panasonic releases a firmware update later this year.

Credit: / Lee Neikirk

The CX850—equipped with full-array local dimming—puts emphasis on a subtle, accurate picture over overt flashiness.

But unlike most of the high-end 4K/HDR TVs we've reviewed this year—many of which have heavily emphasized their spectacular brightness and intense color ranges—the CX850 takes a subtle approach, with a focus on consistency over flashy settings. The most striking thing about the CX850 isn't how it looks—it's how it doesn't look.

Viewing Experience

Outside of some cable content and 4K footage on Netflix, I primarily watched Blu-rays during evaluation. I focused specifically on Ridley Scott's Prometheus, a film that's received acclaim for its visual beauty and relatively demanding scenes.

Considering it's a 4K HDR TV that's upscaling most content, interpreting color spaces that are smaller than its native range, and allocating standard dynamic data along an HDR-capable processor, the CX850 looks refreshingly natural, comfortable, and accurate. In fact, I kept forgetting that it was a 4K model at all, as even very small, detailed elements looked neither too soft nor too sharp.

The CX850 looks refreshingly natural, comfortable, and accurate.

To hammer it home, I watched a large chunk of Scott's latest sci-fi epic side-by-side on this TV and our reference plasma. I found that picture elements requiring vital accuracy—such as white balance, low-light colors, and flesh tones—were virtually identical between the two, and this was before the TV had been calibrated.

For example, around 34 minutes into Prometheus, a pitch black screen slowly yields to the presence of bobbing flashlights as the crew explores an alien cave. The CX850 and plasma looked just about identical here, yielding similar low-light color and white balance. On the other hand, I did notice a bit more blue in the CX850's shadows than the plasma (at the 35:59 mark), but it's only noticeable when viewed side-by-side.

One area where the CX850 couldn't keep up with our reference plasma was motion performance. While this Panasonic handles motion as deftly as most LCD TVs these days, things look choppy sometimes, especially when it's upscaling. Fortunately, I found that Panasonic's motion software does wonders to smooth judder, and on the "Low" setting is splendidly subtle.

Local Dimming

While it can produce extremely deep black levels given the proper content, the CX850's dimming function tends to err on the side of detail preservation. So while it doesn't achieve the intense black levels of an OLED TV or even more aggressive FALD LED options, it usually makes up for this lack of completely inky depth by way of well-preserved shadow details.

Credit: / Lee Neikirk

The CX850 only has 12 dimming zones, so more often than not the TV must make a difficult choice between very dark and brighter scenes, resulting in visible luminance shifts in things like letterbox bars.

But as we've seen with many full-array LED options, the CX850's dimming algorithm doesn't always play nice with test patterns. It's sensitive enough that the presence of, say, the menu interface on the screen during content changes the appearance by a small but noticeable degree. So while the TV is calibrated to proper theater room gamma—it allocates luminance to compliment shadowy details—it occasionally behaves oddly during unusual types of content with lots of white or gray on the screen, such as a hockey game.

To put it more simply, the luminance of shadows—and especially letterbox bars—tends to jump around quite a bit depending on the brightness of the scene at hand. The TV is aiming to maximize contrast without blowing out or crushing details, but much of the time this makes for high visibility in terms of the dimming function, which can easily break immersion during a TV show or movie. Naturally, it's less apparent outside of pitch-black environments.


Less difficult scenes, such as bright, full-field shots like this one, look great. The TV's dimming is better at full-on than a mix of on and off.

In fact, it's safe to say that the CX850 falls short of last year's AX900 in terms of dimming performance. Offering but 12 dimming zones in the 55-inch, the function's subtle approach saves face in many instances, but doesn't entirely avoid common dimming problems such as floating letterbox bars and occasionally very notable shifts in scene luminance during transitions.

Essentially, Panasonic's dimming algorithm simply isn't up to snuff with some of the competition, such as Vizio's M Series.

Lab Results

Testing in a controlled lab environment corroborated the viewing experience, to a degree. A full evaluation of the TV's abilities revealed many strengths, but also a few weaknesses. For one, unlike Panasonic's AX900, the CX850 uses a panel type that offers excellent contrast, but which drops off as you move off-center.

That's not to say you can't still watch this TV from an angle, but the viewing cone is limited. From a typical viewing distance of about 10 feet away, you can only sit around 4 feet to the left or right of center viewing before the TV starts to look a bit washed out.

Where color is concerned, testing proved that the CX850 does indeed focus on accuracy over flash. Though while its white balance was extremely accurate out of the box, the TV's color production was just a little off in the picture modes we tested, tending to either overshoot green or render blue with a little too much magenta.


Lab testing revealed that the CX850 is capable of very accurate gray/white tracking and HD color.

Naturally this isn't a deal-breaker for 99% of viewers, but it's unusual. Thanks to the extra color this TV produces via LED phosphor tech, it's very easy for the CX850 to produce the proper HDTV color points by simply reigning in its wider native color space, as we found during calibration. Despite the TV's multiple picture modes, none of them are 100% accurate per HD color, but instead tend to drift between various approximations depending on the mode you select.

The Verdict

A supreme dedication to accuracy deserves praise, but this TV may struggle to find an audience.

In a world where the brightest and flashiest 4K TVs tend to turn the most heads, the CX850's even-keeled presentation and razor-sharp focus on accuracy is practically Promethean. It's strikingly similar to what we saw with last year's incredible $8,000 Panasonic AX900, and the promise of that kind of quality—for half the price—is enough to set tongues wagging.

Unfortunately, while the CX850 wins accolades in many performance areas, the name of the LED game in 2015 is "local dimming," and it doesn't entirely make the grade in that regard. For example, when local dimming was set to low the TV retained shadow detail beautifully, but the letterboxes above and below content remained too bright. If we ramp the dimming up to remove this, the letterboxes improve, but subtler elements are occasionally too dark.


These issues aren't so egregious that you'll notice them often in normal lighting, but things can be less-than-ideal for videophiles looking for dark- or dim-room viewing. That's not entirely a dealbreaker—few people have jet-black home theater setups—but given how good the AX900 is, and how far local dimming has come this year, we were hoping for better.

At the end of the day, the CX850 earns our respect for its careful preservation and accuracy during 1080p and 4K playback, but we're also concerned that it's suffering from a bit of an identity crisis. The color accuracy and adherence to standards will please pickier viewers, but the dimming function may be a turn off, and at this price casual viewers will likely gravitate towards Samsung's JS9000 or Vizio's M Series.

Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.
Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.
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Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.
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