The TCL 6 Series/R646 2021 QLED is a 4k TV with Mini LED backlighting. It's part of the 6 Series lineup that includes the TCL 6 Series/R635 2020 QLED, with one of the differences being that the R646 has Google TV while the R635 uses Roku TV. While the TV is an overall improvement from the R635 thanks in part to its better local dimming feature, it's still not as good as other flagship 4k TVs. The Google TV interface is user-friendly, but we've read reports of issues with apps crashing. The TV has a built-in mic that you can use with Google Assistant, but you also have the option to disable the mic if you're worried about privacy. TCL also includes current-gen gaming features like variable refresh rate (VRR) support and two HDMI 2.1 inputs, meaning you can take full advantage of the Xbox Series X and PS5's capabilities.
The TCL 6 Series/R646 is great for most uses. It's impressive for watching movies because it displays deep blacks, and it has a decent Mini LED local dimming feature, but it doesn't improve the picture quality that much. It's great for watching TV shows or sports because it has fantastic peak brightness and excellent reflection handling, but it has narrow viewing angles. Gamers should appreciate the VRR support, HDMI 2.1 inputs, and low input lag. Lastly, it's impressive for watching HDR content because it displays a wide color gamut and gets bright enough to make highlights pop.
The TCL 6 Series/R646 is impressive for watching movies in dark rooms. It has an outstanding contrast ratio to display deep blacks, and the Mini LED local dimming feature is decent, but it doesn't improve the picture quality that much. It removes 24p judder from any source, and it displays 1080p and 4k content well, so it's great for watching Blu-rays and Ultra HD Blu-rays. However, it can't properly display 480p content, so it's not a good choice for watching DVDs.
The TCL 6 Series 2021 is great for watching TV shows in bright rooms. It gets bright enough to fight glare and has excellent reflection handling, so visibility shouldn't be an issue. The Google TV is great to use and has a ton of apps available to download, and it doesn't have issues upscaling 720p content. Sadly, it has narrow viewing angles, so the image looks washed out from the sides.
The TCL 6 Series TV is great for watching sports in a well-lit environment. Thanks to its excellent reflection handling and fantastic peak brightness, visibility shouldn't be a problem even in the brightest of rooms. It has a great response time, but some motion may still look blurry. Unfortunately, it's not a good choice for watching sports with a large group of friends because it has narrow viewing angles.
The TCL R646 is excellent for gaming. It has a 120Hz panel with HDMI 2.1 inputs, meaning you can take full advantage of the PS5 and Xbox Series X's capabilities. It has VRR support to reduce screen tearing, and the input lag is low. It has a quick overall response time, but there's black smearing with fast-moving objects in dark scenes. It's excellent for dark room gaming because it has high native contrast and decent local dimming.
The TCL 6 Series is impressive for watching HDR movies. It has a VA panel with a high native contrast ratio, and even though it has a decent Mini LED local dimming, it doesn't improve the picture quality in dark scenes that much. It displays a wide color gamut, and it gets bright enough to make highlights pop. It supports Dolby Vision and HDR10+, so you won't have to worry about which format the HDR content is in before watching.
The TCL 6 Series is excellent for HDR gaming. It has a bunch of gaming features like HDMI 2.1 inputs and VRR support to reduce screen tearing. It has low input lag and a quick response time, but you may notice some black smearing. HDR content looks great because it gets bright enough to make highlights pop, displays a wide color gamut, and has high contrast. It has a decent full-array local dimming feature, but it doesn't seem to improve the picture quality all that much in dark scenes.
The TCL 6 Series is great to use as a PC monitor. It has a low input lag for a responsive desktop experience, and it has a quick response time, but you may notice some motion blur. Glare shouldn't be an issue in well-lit rooms because it gets bright enough to combat glare and has excellent reflection handling. It displays proper chroma 4:4:4 with 1080p and 4k signals at 60Hz, but not any other signal. It also has narrow viewing angles, so the image looks inaccurate from the side.
The TCL 6 Series/R646 is a new TV in TCL's 6 Series Mini LED QLED lineup. The TCL 6 Series/R635 2020 QLED is in the same lineup, and the main difference is that the R646 has Google TV, and the R635 uses Roku. There's also the R648, which is an 8k model that uses Roku. This TV mainly competes with the Hisense U8G, but you can also find the Sony X85J and the Vizio P Series Quantum 2021 in the same price range.
The TCL R646 features new metal feet that don't take up as much space as those on the TCL 6 Series/R635 2020 QLED. They support the TV well, and there's minimal wobble. There's 3.5 inches from the table to the bottom of the screen, and even with a soundbar placed in front, we could still use the remote and voice control properly.
Footprint of the 55 inch TV: 40.35" x 12.48"
This is a bulky TV that won't sit flush against a wall because the bottom part near the inputs sticks out.
It has good build quality, and it feels very similar to the TCL 6 Series/R635 2020 QLED. It's well-put-together, and it feels sturdy for the most part. The feet are good, as there's almost no wobble. However, the plastic on the back flexes quite easily, and it's noticeable with both the glossy top and the textured bottom.
It has an outstanding native contrast ratio. It displays deep blacks, and the local dimming feature helps it achieve high contrast with our checkerboard test pattern. Keep in mind that contrast can vary between units.
Note: As explained in the Local Dimming section, the local dimming feature doesn't seem to improve the picture quality too much in real scenes. We're measuring a high contrast with the checkerboard test pattern, but it's not entirely representative of the performance in real content.
The SDR brightness is fantastic, so glare shouldn't be an issue in most bright rooms. It gets brightest with small highlights, as seen in the 10% and 25% windows, and even though brightness varies a bit between scenes, it shouldn't be too distracting.
We tested the SDR brightness after calibration in the 'Movie' Picture Mode with Brightness and Contrast at their max, Local Contrast on 'Low', the Color Temperature set to 'Warm -5', and Gamma on '2.2'.
You can achieve a slightly brighter image by setting Local Contrast to 'High' and Color Temperature to 'Cool 4'. We measured 1,180 cd/m² in the 25% window using these settings, but this comes at the cost of losing image accuracy.
The TCL 6 Series/R646 has a decent full-array local dimming feature. It has Mini LED backlighting like the TCL 6 Series/R635 2020 QLED, but it's an improvement overall. There are 128 zones on the 55 inch model, and the larger sizes may have more. Overall, it helps improve the contrast with our checkerboard pattern, but it doesn't seem as good as other TVs in improving the overall picture quality in dark scenes. There isn't much black crush because it seems that it raises the black level in scenes with bright objects, and it's almost as if the local dimming feature isn't doing enough. However, there's not much blooming around bright objects as the zones average out the black level. Subtitles also look good.
Uniformity is good, and you don't lose many details in scenes like a star field. Fast-moving objects transition between the zones well, and even though you may notice the transitions more with our pattern, it's not as noticeable in real content.
We recommend setting the local dimming, called Local Contrast, to 'Low' because the 'High' setting is more aggressive, resulting in too much black crush and blooming. However, with some real content, the difference is minimal, so you should choose whichever setting you prefer. We also measured the contrast in SDR and HDR with both settings:
However, these measurements are high and don't reflect entirely its performance with real content.
The local dimming in Game Mode is decent, and it performs the same as out of Game Mode. Once again, we recommend setting Local Contrast to 'Low'.
The TCL 6 Series has impressive HDR peak brightness. It doesn't get much brighter than in SDR, but it's still enough to make highlights stand out in HDR. We verified the real scene brightness to make sure the measurement was correct, and it was. The EOTF follows the target PQ curve nearly perfectly until the slow roll off at the peak brightness, so you don't lose too many details in bright scenes.
We measured it using the 'Movie' HDR Picture Mode with the Brightness and Contrast at their max, Local Contrast on 'Low', and Color Temperature on 'Warm -5'. There are two settings called Micro Contrast and Black Stretch that are meant to optimize the contrast and brightness, and we measured our checkerboard pattern with them, and they don't make much of a difference, if any.
If you find the image too dim, use the same settings as above, but with Dynamic Tone Mapping enabled and the Gamma set to '1.8'. This results in a much brighter EOTF, but it doesn't change the peak brightness.
The HDR brightness in Game Mode is excellent. It scores 0.1 better than outside of Game Mode because the real scene highlight is slightly brighter, but the visible difference is minimal. We tested it using the same settings as outside of Game Mode.
The gray uniformity is good. There aren't many visible issues here, except for some darker edges, but it's hard to tell. Uniformity is better in near-dark scenes. Keep in mind that uniformity can vary between units.
The black uniformity is good. Without local dimming, there's backlight bleed in the corners, and the local dimming feature helps eliminate that issue. With local dimming, you can see how it doesn't deliver perfect blacks, but there's less blooming than on the TCL 6 Series/R635 2020 QLED.
The TCL 6 Series 2021 has narrow viewing angles, which is expected from a VA panel. The image looks inaccurate if you're viewing it from the sides.
The reflection handling is excellent, and it's much better than the TCL 6 Series/R635 2020 QLED. It does a much better job at absorbing light, so combined with the high peak brightness, visibility shouldn't be an issue.
The TCL 55R646 has good out-of-the-box accuracy, but this can vary between units. Most colors are only slightly inaccurate, and the color temperature is close to the 6500K target. However, white balance is off, which affects the shades of gray, and gamma doesn't follow the 2.2 target well, so most scenes are darker than they should be.
The accuracy after calibration is fantastic. Color accuracy and the color temperature improved, and the white balance is much better too. Gamma is perfect for most scenes, but some really bright scenes are a bit too dark.
See our recommended settings here.
Unfortunately, the TCL 6 Series 2021 doesn't properly display 480p content. When we try to display an 852x480 resolution with a 16:9 aspect ratio from our PC, it upscales it to an 800x600 resolution with a 4:3 aspect ratio. We tried to change the Aspect Ratio settings on the TV, but everything looked off. The above image is a crop, but you can see the original with the black bars here. You can also see what the 4:3 image looks like here.
Fortunately, there aren't any issues with 720p content, like from cable boxes.
This TV displays native 4k content perfectly as there aren't any issues.
This TV uses a BGR subpixel layout, which can affect how text is displayed when using the TV as a PC monitor. You can read about it here.
This TV has a great color gamut for HDR content. It has fantastic coverage of the commonly-used DCI P3 color space, and tone mapping is good, too, so colors look accurate. Coverage of the wider Rec. 2020 is more limited, but it's still decent.
The color volume is good. Thanks to its high peak brightness, it displays bright colors well, but it can't display extremely dark colors like an OLED because it doesn't have a near-infinite contrast.
Update 10/19/2021: We retook the gradient photo on an uncalibrated HDMI port, as the calibration appears to have caused a few flaws in the original photo. It didn't result in any changes to our results, but the photo is more consistent with our other reviews.
The TCL R646 has good gradient handling, and it's a significant improvement over the TCL 6 Series/R635 2020 QLED. There's obvious banding in the test pattern with the darker shads of each color, but it only seems to be happening at certain steps and not in between. Setting Gradation Clear to 'Low' or 'High' helps improve the banding in the test pattern and real content, but that comes at the cost of losing details.
Unfortunately, there are some signs of temporary image retention after displaying a high-contrast static image, but most of it disappears quickly. However, this can also vary between units, so your experience may be different.
We don't expect VA panels to experience permanent image retention, as the VA panel in our long-term test appears immune.
The TCL R646 has a great overall response time. There's overshoot in most transitions, but the 0-100% transition is slow, resulting in black smearing, which is typical of VA panels.
The TCL R646 uses pulse-width modulation (PWM) to dim its backlight in any picture mode. It flickers at all backlight levels, including at its max. However, the flicker frequency is so high that most people won't notice it.
There's an optional backlight strobing feature, commonly known as black frame insertion. It only flickers at 120Hz and it creates noticeable image duplication, but it doesn't dim the screen much. Our BFI scoring is based on the flicker frequency,
There's a motion interpolation feature to interpolate 30 fps and 60 fps content up to 120 fps. It's not bad overall, but it still creates artifacts in fast-moving scenes. We tried to measure the flicker frequency with the motion interpolation feature, but there's so much noise we couldn't measure it properly.
Due to the quick response time, there's some stutter with lower-frame rate content because each frame holds on for longer. Enabling the motion interpolation feature can help reduce this.
It automatically removes 24p judder from any source, and no extra setting is needed.
It has variable refresh rate support to reduce screen tearing. TCL doesn't specify which formats it supports, but we confirmed with our Radeon PC that it supports FreeSync. VRR also works with the Xbox Series X, but because the Xbox supports both HDMI Forum VRR and FreeSync, there's no way to know which one is working and if it supports HDMI Forum VRR or not. It's also unclear when VRR is working because no prompt pops up on the TV, but we confirmed with the pendulum test video and in games that VRR works.
The TCL 6 Series/R646 has very low input lag in Game Mode. It's an improvement from the TCL 6 Series/R635 2020 QLED, and you shouldn't notice any delay when gaming. We had issues with our VRR input lag testing because the HDMI Forum VRR may have been active, so our results were a bit more inconsistent than normal, which is done with FreeSync. However, the results are still in line with what we expect.
The TCL 6 Series supports any resolution up to 4k @ 120Hz, as long as you set the HDMI Mode to 'HDMI 2.1' to reach the full bandwidth. It displays proper chroma 4:4:4 with 1080p and 4k signals at 60Hz, but it can't do it with any other signal. It accepts a 4k @ 120Hz signal in 10 or 12-bit color depth with chroma 4:4:4, but it doesn't properly display chroma 4:4:4 because text looks a bit fuzzier than what we would expect.
Update 10/19/2021: We've received a few requests to check for resolution halving in certain games. We tried it with Destiny 2 on an Xbox Series X and didn't notice any signs of resolution issues; 4k @ 120Hz is displayed properly.
This TV supports any signal from the Xbox Series X and PS5 up to 4k @ 120Hz. As mentioned in the Variable Refresh Rate section, no VRR signal shows up on the screen when it's working.
The Composite In input needs an adapter, but it doesn't come with one.
This TV supports eARC, allowing you to pass DTS:X and Dolby Atmos audio formats to a compatible receiver using a single HDMI connection. During our testing, our receiver wasn't properly playing the Dolby Atmos audio file, but the Dolby Atmos logo popped up on the TV. This is likely an issue on our end, and we expect it to work for most people. Since TCL advertises the Dolby Atmos support, we list it as 'Yes', but if you experience the same issue, let us know.
The frequency response is decent. It's similar to the TCL 6 Series/R635 2020 QLED, but it gets louder and has a bit higher deviation, but the sound profile is still well-balanced. It has decent bass, but it's still nothing like a dedicated subwoofer.
The distortion performance is great. Even at the max volume, there's hardly any distortion. However, this depends on the content and not everyone may hear it.
Unlike the TCL 6 Series/R635 2020 QLED, the TCL 6 Series/R646 comes with Google TV. TCL uses its own implementation of Google TV, so the settings menu is different than on Sony and Hisense TVs. It may take some time to get used to, but menu navigation feels very smooth.
We read reports of people experience a ton of bugs with the Google TV. We didn't notice any, but if you do let us know.
There are ads on the home page, but we couldn't get a photo of them during testing because they pop in and out, and they're not always there.
The Google Play App store has a massive selection of apps available to download.
The remote is new and is rather simplistic. It has a few shortcut buttons, and the navigation buttons may seem unclear at first as to what they do. There's a built-in mic for voice control, and you can ask it to change inputs, open apps, and search for content, but you can't ask it to change settings.
There's a built-in mic in front of the TV that you can use for the Google Assistant feature, as long as the TV is on.
The power button is on the back of the TV on the right, and you can change inputs with it too. There's the switch to turn the built-in mic on and off above it.
We tested the TCL 55R646, and for the most part, we expect our review to be valid for the 65 inch and 75 inch models. This model is a 4k TV with Google as its smart platform, and it's part of the 6 Series lineup that includes the TCL 6 Series/R648 2021 8k QLED and the 4k R635, both of which include Roku TV. The R635 is a 2020 model that TCL still produces in 2021. Our results aren't valid for those variants.
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If someone comes across a different type of panel or if their TCL R646 doesn't correspond to our review, let us know, and we'll update the review. Note that some tests, like gray uniformity, may vary between units.
The TCL 6 Series QLED is a great 4k TV with quantum dot technology and Mini LED backlighting that doesn't cost as much as Samsung TVs with those features. The inclusion of Google TV is a nice addition for those who aren't a fan of Roku, and it has great gaming features. However, it's just not there yet as a top TV because its local dimming feature isn't as good as the competition.
The Hisense U8G and the TCL 6 Series/R646 2021 QLED are both great TVs. They're fairly similar overall, but there are a few differences between them. Even though the TCL has Mini LED backlighting, the Hisense has a better local dimming feature because it doesn't raise the black level as much when there are bright objects. The TCL has better contrast, but the difference isn't as noticeable with real content. The TCL also gets brighter, but the Hisense has better reflection handling. While the Hisense uses Android TV and the TCL has Google, they're very similar, and the only differences are aesthetic.
The LG C1 OLED and the TCL 6 Series/R646 2021 QLED are different types of TVs. The LG is a premium OLED with a near-infinite contrast, perfect black uniformity, and wide viewing angles. It also has much better motion handling than the TCL because it has a near-instantaneous response time. On the other hand, the TCL uses an LED panel that gets much brighter and doesn't suffer from the risk of permanent burn-in. Although they each have HDMI 2.1 inputs and VRR support, the LG has a wider VRR range that lets it go below 20Hz.
The TCL 6 Series/R646 2021 QLED and the Sony X90J are both great TVs. They each have a VA panel with a high contrast, and even though the Mini LED local dimming feature on the TCL does a better job at improving the contrast on our checkerboard pattern, the local dimming on the Sony performs better overall. The TCL gets brighter and has much better reflection handling, making it a better choice in well-lit rooms. It also has more gaming features like VRR support, but that may come in a future firmware update for the Sony. The Sony has better color accuracy, and it does a much better job at upscaling 480p content, so it's better for watching DVDs.
The TCL 6 Series/R646 2021 QLED and the Hisense U7G are both great TVs. The TCL is a flagship 4k TV, so it's better in a few areas, like its higher HDR peak brightness. The TCL has Mini LED backlighting, but the local dimming feature on each are both decent. The TCL gets brighter in SDR and has better reflection handling, so it's a better choice for well-lit rooms. On the other hand, the Hisense has a wider VRR range, and it doesn't have any issues displays 480p content like the TCL.
The TCL 6 Series/R635 2020 QLED and the TCL 6 Series/R646 2021 QLED sit alongside each other in the TCL 6 Series lineup. The R646 was released a year after the R635, so it improves in a few areas. The main difference is that the R646 has much better local dimming as there's less blooming around bright objects, but it doesn't deliver as deep blacks with local dimming enabled. The R646 also has two HDMI 2.1 inputs, which the R635 doesn't have, meaning you can use it for 4k gaming up to 120 fps. They each have different smart systems, with the R646 using Google TV and the R635 using Roku.
The Samsung QN90A QLED is better overall than the TCL 6 Series/R646 2021 QLED. They each have Mini LED backlighting, but the full-array local dimming feature on the Samsung has more dimming zones, so it produces deeper blacks in real content and has less blooming. It also has wider viewing angles thanks to Samsung's 'Ultra Viewing Angle' technology, but that means the TCL has a better native contrast ratio. The Samsung gets much brighter, especially in HDR, so it makes highlights pop more. TCL has one more HDMI 2.1 input compared to the Samsung, and even though it also has VRR support, its refresh rate range is more narrow than the one on the Samsung.
The Hisense U6G and the TCL 6 Series/R646 2021 QLED are both great TVs. They have similar characteristics, but there are a few differences between them. The TCL has Mini LED backlighting that allows it to get much brighter, especially in HDR, making highlights pop more. They each have decent local dimming features, but the one on the Hisense does a better job at displaying deeper blacks than on the TCL. The Hisense also doesn't have issues upscaling 480p content, which the TCL has issues. The main advantage the TCL has over the Hisense is a 120Hz panel with HDMI 2.1 inputs and VRR support, none of which the Hisense has.
The Sony X95J and the TCL 6 Series/R646 2021 QLED are both great LED TVs. The Sony is a flagship model with Sony's 'X-Wide Angle' technology that allows it to have much better viewing angles than on the TCL. Even though the TCL has Mini LED backlighting, the local dimming is much better on the Sony because it improves the picture quality in dark scenes. Each TV has HDMI 2.1 inputs, but the TCL has more gaming features like VRR support, which the Sony doesn't currently have, and lower input lag.
The TCL 6 Series/R646 2021 QLED is better overall than the Sony X85J. The TCL has more features like Mini LED backlighting to make it brighter and a full-array local dimming feature, which the Sony doesn't have. The TCL also has better reflection handling, so it's a better choice for well-lit environments. They each have HDMI 2.1 inputs, but the TCL has VRR support, which the Sony doesn't have, but it may come in a future firmware update.
The TCL 6 Series/R646 2021 QLED is better than the TCL 5 Series/S535 2020 QLED. The R646 is a higher-end version, so it has more features like HDMI 2.1 inputs, VRR support, and a 120Hz panel for a superior gaming experience. It uses Mini LED backlighting that lets it get much brighter, especially in HDR, so highlights pop more. They each have decent local dimming features that perform similarly to each other because they raise the black levels in dark scenes to reduce blooming, but that comes at the cost of not having deep blacks.
The Sony X950H and the TCL 6 Series/R646 2021 QLED are both great TVs. The TCL has a higher contrast ratio than the Sony because the Sony uses viewing angle technology to improve the viewing angles at the cost of the contrast, so the TCL displays deeper blacks. However, the local dimming feature on the Sony still seems to be more effective at improving the picture quality in dark scenes. The Sony has more accurate colors, and it doesn't have issues displaying 480p content like the TCL. However, the TCL comes with more gaming features out-of-the-box like HDMI 2.1 inputs, VRR support, and lower input lag.
The Samsung QN85A QLED and the TCL 6 Series/R646 2021 QLED are both great TVs with different panel types. The TCL has a VA panel that lets it display deeper blacks, while the Samsung has an IPS-like panel with wide viewing angles instead. The Samsung still displays deep blacks thanks to its decent Mini LED local dimming feature, but there's blooming around bright objects. The Samsung also gets brighter and has improved reflection handling, so it's a better choice for well-lit rooms. It doesn't have any issues upscaling lower-resolution content from DVDs either, which the TCL has problems with.
The Sony X900H and the TCL 6 Series/R646 2021 QLED are two great TVs. The TCL features Mini LED that allows it to get brighter and, combined with the better reflection handling, is a better choice for well-lit rooms. Despite the Mini LED backlighting, the Sony has a better local dimming feature because it doesn't raise the black levels like on the TCL. They both have similar gaming features with HDMI 2.1 inputs, a quick response time, and low input lag. Both TVs have VRR support, but you have to update the Sony to receive it.
The TCL 6 Series/R646 2021 QLED and the Hisense H9G are both great. They each have VA panels that display deep blacks, but the local dimming feature on the Hisense is much better at improving the picture quality in dark scenes with minimal blooming. Motion looks smoother on the Hisense thanks to the quicker response time, but the TCL has more gaming features like two HDMI 2.1 inputs and VRR support, meaning you can use the current-gen gaming consoles to their full capabilities. The Hisense is a better choice for watching DVDs because it doesn't have issues upscaling lower-resolution content the way the TCL has.
The LG CX OLED is better overall than the TCL 6 Series/R646 2021 QLED, but they use different panel technologies, each with advantages and disadvantages. The LG has an OLED panel with a near-infinite contrast, perfect black uniformity, and wide viewing angles. On the other hand, the TCL uses an LED panel that gets much brighter and doesn't suffer from the risk of permanent burn-in. Even though they each have HDMI 2.1 inputs and VRR support, the LG has a wider VRR range that allows it to go below 20Hz. The LG also has a much quicker response time for smoother motion.
The TCL 6 Series/R646 2021 QLED sits higher up in the lineup than the TCL 5 Series/S546 2021 QLED, so it has more features and better performance. The main differences are that the R646 has Mini LED backlighting and has HDMI 2.1 inputs, allowing you to play higher frame rate games than the S546. The local dimming features perform similarly as they raise the black level in real content, but there's less blooming on the R646. The R646 also gets brighter and has much better reflection handling, so it's a better choice for well-lit rooms. The built-in speakers are also much better on the R646, but that won't make a difference if you get a soundbar or receiver anyways.
The Samsung Q80/Q80T QLED and the TCL 6 Series/R646 2021 QLED are both great. They have similar panel types, but the TCL has a better native contrast because the Samsung uses the 'Ultra Viewing Angle' technology to improve the viewing angles at the cost of the contrast. Still, they each have decent local dimming features and very good gray uniformity, making them great for watching movies. They have similar gaming features with HDMI 2.1 inputs and VRR support, but the VRR range is wider on the Samsung because it can drop below 20Hz.
The TCL 6 Series/R648 2021 8k QLED and the TCL 6 Series/R646 2021 QLED are part of the same 6 Series lineup, but they're different TVs. The R648 is an 8k model with Roku TV, while the R646 is a 4k TV with Google built-in. They each have VA panels with high contrast, and even though their local dimming features are both decent, they perform differently. The one on the R648 crushes blacks with minimal blooming and the one on the R646 helps brighten highlights, but it doesn't improve the contrast with real content much. They both don't upscale 480p well, but that's because the R646 can't display the proper aspect ratio, and the R648 is just bad at it.