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Black Uniformity of TVs
Clouding and Flashlighting

What it is: Evenness of blacks.
When it matters: Dark scenes viewed in a dark room.
Score components:

Black uniformity refers to a TV’s ability to display solid black all across its screen. Perfect black uniformity would mean shadows, night skies, and other black objects would look equally dark at any given point on the screen, and that the TV’s lighting is perfectly diffused across the screen. Unfortunately, all LED TVs have some imperfections, including flashlighting, which looks like a flashlight is pointed across the corners of the television; and clouding, which looks like brighter patches on parts of the screen. Both are caused by the TV improperly diffusing the backlight across the entire screen, and both are especially obvious when the TV is being viewed in a dark room.

For this test, we take a photo of the TV while it displays a mostly black frame, and we also calculate the standard deviation of the color values of the pixels when they try to display black.

Update 21/04/2017: Renamed  'Black Uniformity' to 'Native black Uniformity'. Also added a 'Black Uniformity with Local Dimming' test to demonstrate the black uniformity performance when the local dimming feature is turned on. We plan to start scoring this at the next scoring update. The analysis of the test picture is the same as the 'Native Black Uniformity'. 

Test results

For older models, see our results for 2013 and 2014 TVs.

When it matters

TV with clouding and flashlighting problems Bad black uniformity (6.352%)
LG UF8500
Good black uniformityGood black uniformity (0.707%)
Samsung J6300

Black uniformity issues like clouding or flashlighting can only be seen during dark scenes, and only when the TV is being watched in a dark room. If you watch TV in a room that gets a bit of light, this isn’t so important.

No LED TV has a perfect uniformity, but in most cases, you won't notice it unless you really look for it. However, some TVs (like on the above, left) have exceptionally bad black uniformity. If you get something that bad, it will make a big difference in how much you enjoy what you are watching.

Our tests

Native Black Uniformity Picture

Our picture test captures the black uniformity imperfections on a TV’s screen, and is meant to show you what the quality of the blacks is in terms of what you actually see. Of our two black uniformity tests, we consider this the most useful for most people.

To evaluate the black uniformity on TVs, we take a photograph of this pattern, in a pitch dark room, with the following camera settings: F4.0, ISO-200, 2 sec shutter time. The backlight of the TV is set so that white emits 100 cd/m2 of light. In order to show the TV’s true uniformity, we don't turn on local dimming for this test (the local dimming feature is scored separately in our reviews).

The camera settings we use were chosen so that what you see in our picture reflects what you see in a dark room.

Black uniformity test patternOur black uniformity test pattern

Native Black Uniformity Std. Dev.

What it is: Average of the squared difference of the blacks.
When it matters: Dark scenes viewed in a dark room.
Good value: < 2%
Noticeable difference: 1%, but keep in mind that it varies a lot by unit, even of the same model; yours likely will not end up exactly like ours.

We also calculate the standard deviation of the color values of the pixels from the picture taken in the test above. This is done so that we can objectively score the TVs for uniformity, rather than needing to rely on our subjective opinions of each TV. This is a bit less useful for people who want an idea of what black uniformity looks like, but is necessary for us to be able to assign a fair score.

To score the TV clouding and flashlighting issues objectively, we process the photograph from above and calculate the standard deviation of the pixels in the picture. The result is a number that corresponds to how uniform the blacks are. A value of 0 means it is perfect. The greater the number, the more the blacks vary.

Black Uniformity with Local Dimming Picture

Similarly to the native black uniformity test, we take a picture with the same room and camera settings, but this time with the local dimming feature turned on and set to maximum.

This is useful to show how the local dimming is effective to get rid of black uniformity issues when displaying a black image when viewed in a dark room.

Black Uniformity with Local Dimming Std. Dev.

What it is: Average of the squared difference of the blacks with Local Dimming enabled
When it matters: Dark scenes viewed in a dark room.
Good value: < 2%
Noticeable difference: 1%, but keep in mind that it varies a lot by unit, even of the same model; yours likely will not end up exactly like ours.

We calculate the black uniformity with local dimming standard deviation the same way we do the native black uniformity standard deviation, but this time base on the black uniformity with local dimming picture. This is not perfect as almost all TVs with local dimming experience some blooming around the white cross.

Additional information

LED vs OLED black uniformity

LED backlit LCD TVs are prone to this issue, but it isn't a problem on OLED TVs, because the pixels are self-emitting, and therefore don't need to worry about improper implementation of a backlight.

The cause of flashlighting and clouding

Flashlighting and clouding can occur for a few reasons:

  • Poorly designed backlight placement. The type of the backlight and the position of it directly affect the uniformity of the screen. The worst uniformity can be found in edge-lit LED TVs, because the LEDs are only on the edge of the screen. Full-array LED TVs have good uniformity because their LEDs are spread out across the whole screen. This is less true today, though. Some edge-lit TVs have great uniformity. You can learn more about different backlights here.
  • Non-uniform frame pressure. Both the LCD screen and the diffuser layers are somewhat flexible. A slight difference in pressure on the frame of the television can change the uniformity of the picture. On some televisions, this can be fixed (see below).
  • Uneven intensity of the lighting. Sometimes, the intensity between two lighting components can vary in a set (for example, one LED could be slightly brighter than an LED next to it). This is less likely to happen with a brand new TV, but can start appearing over time if some components age and degrade faster than others.

How to get the best results

Flashlighting can sometimes be fixed on some televisions. If your flashlighting issue is caused by an issue with the frame’s pressure, you can adjust it by slightly loosening or tightening the screws behind the edge of the screen. Some televisions do not expose the screws, however, so you won’t have that option with those. You should also keep in mind that a small change in the tightness of a screw can have a big impact on the uniformity of the screen, so be careful if ever you do try this step.

For clouding, there's a pretty simple fix that - while not guaranteed - can have good results. Power on the TV and display a black image. This will allow you to see the lighter spots on the screen. Next, take a soft cloth and massage those brighter spots to improve the uniformity. You should only apply very gentle pressure, just barely touching the screen. You can also try a few different stroking patterns. If you are patient enough, this works surprisingly often, especially on edge-lit TVs.

Alternatively, you might consider returning or exchanging your television. Some models are more prone than others to having issues. Even within the same model, some units can have more of this issue, because of a slight variance in the manufacturing or the shipping process. It can be worth trying to exchange it for the same model before going with an entirely different one. Extreme cases of clouding are also covered under a TV's warranty.

Related settings

  • Reducing 'Backlight' can help mask the problem by making the whole screen darker.
  • The local dimming feature, if the TV is equipped with it, can also help. We talk about local dimming in more detail here.

Other notes

  • All LED TVs have black uniformity problems.
  • The bigger the LED TV, the more likely it is to have uniformity issues.
  • Backlight uniformity issues don't increase over time unless a large amount of stress is put upon the panel (like in the case of a big temperature swing, or if the TV is moved).
  • Sometimes, just letting the TV settle for a few days after unpacking it can solve the issue. This is especially true if the TV is laid on the side during shipping/moving.

Conclusion

A TV’s black uniformity refers to how evenly a TV can display black all across the screen. It’s important when watching dark scenes in a dark room, and while most people shouldn’t notice black uniformity issues like flashlighting and clouding, they can become more apparent when the issues are especially bad. You won’t need to worry about these problems in rooms with lights on, though. For each TV, we take a photo of a black frame in order to capture the black uniformity, and then we calculate the color values of the pixels in order to find the standard deviation of the uniformity.

You may be able to remove flashlighting (to some degree) by tightening the screws of the TV’s frame. This can have pretty dramatic effects on picture, though, so you should be very careful when attempting this. For clouding, gently massaging problem areas with a soft cloth often does a good job of fixing bad uniformity.

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Questions & Answers

23 ANSWERED QUESTIONS
44
Does it go away after few weeks of usage, or should I call for a replacement straightaway?
It rarely goes away.
33
I just purchased one of the new Ultra HD 55" TVs from Samsung and have to return it for a second time. Not really for the clouding issues, that is not too much of a bother, but for the edge light coming through the edge of the frame. Have you heard of any issues with this, and is it able to be fixed without having to return the TV? Because it's really annoying when watching movies.
It depends on what it looks like. If there are patches of brightness along the edges, then it's likely that you're just experiencing some uniformity issues brought on by inconsistent lighting from the LEDs. If you've got light actually coming out of the sides of the TV, then you have a defective TV.
If you send us a photo of the problem, we'll be happy to let you know if what you have is within the bounds of what is normal/acceptable, or if it is something that necessitates an exchange.
31
I'm having trouble determining what 'typical' amounts of clouding may be on a new JS8000 Samsung TV. The images in this album show the TV displaying a flat black jpeg at ISO200 and automatic ISO (1800? whatever my iPhone would select) and you can see the stark difference. imgur.com/a/ioSZR This is a relatively foreign phenomenon to me, having come from a plasma tv previously. Does this seem acceptable? I obviously can't notice the clouding with full frame images, but it is subtly noticeable in dark scenes of movies with a black frame on the top and bottom. I'm mostly wondering if a higher quality display (say, the 8500 or sony X850) would carry a similar trait.
The picture we take for our black uniformity test use these camera settings: F4.0 2s exposure time at ISO-200. If you are able to take a picture with the same settings, then you will be able to compare our black uniformity scores/pictures with your own. From your first picture, it doesn't seem that bad.
19
How did you test black uniformity (backlight, contrast ...) of the H7150, and what are the details of published black uniformity pictures (ISO, shutter speed, aperture)? I purchased the H7000 and I want to do the same test, with the same setup and compare with your results. I can notice some minority clouding on my unit - standard, backlight 6, contrast 95, brightness 45. It's in the top right corner, visible only in a completely dark room and during long dark scenes. I am not sure if I should accept it, or if there is any chance of getting a better unit.
The exact picture settings used on the TVs are posted in a sub-page of our reviews. A zip of all our test footage can be found in our 'About Us' page. The camera settings for the black uniformity test are ISO-200, 2" and F4.0, 6500K white balance.
18
My Samsung F7500 also has the same issue. Clouding appeared in the middle of the left side. By pressing the screen it disappeared, to some extent. Shouldn't I press the screen of my TV?
This means the clouding is caused by an uneven pressure across the backlight. Compressing the screen of an LED TV is only an issue when the LCD layer gets compressed (which leaves a temporary print). Some people reported fixing their clouding by gently 'massaging' their screen with a soft cloth. It is worth a try.
15
Do direct-lit LED TVs really have better uniformity than edge-lit TVs?
Yes, direct-lit TVs usually have better uniformity than edge, but even direct-lit TVs are not always perfect.
14
I read somewhere that you can gently rub/massage the clouded areas to remove them. Is this true?
It works sometimes, but not often. It is worth a try. Get a soft cloth and rub gently (with almost no pressure) on the affected areas.
13
In rubbing or massaging the effected area of the screen, is this done while the TV is on so you can see the actual areas, or should it be performed while the TV is off?
You can leave it on, because the pressure shouldn't be high enough to damage it.
11
I didn't understand this. I want to buy an LED TV, but will it have flashlighting? Or dose this happen by chance to this specific TV?
All LCD and LED TVs are subject to this. Edge-lit LEDs are more prone to it. The risk is also higher with bigger TVs. It varies a lot per actual unit, so you might get lucky and get a good one.
11
Where does one view the screen when doing clouding and flash lighting tests? We bought a Samsung 60 inch 7150. Put a black jpg and a grey jpg on the screen and while sitting in a direct line of the screen the picture looks perfect. Start moving to the side and defects such as flash lighting and clouding start to appear. Move to the side and the screen looks almost light grey, with some vertical bands appearing. Should flash lighting and banding not show it face from side viewing or is this normal. Thanks!
This is normal, even though unfortunate. Uniformity issues and colors get worse at an angle for every LED. All of our pictures are directly in axis. You can check out our videos of the viewing angle to also notice the picture becoming white at an angle. If your LED is perfect when in front, this is really good and you got a good one. This is rare by itself! But an LED with perfect uniformity/color at an angle just doesn't exist.
10
Is this flashlighting (or clouding) going to cause more damage over a period of time, or is it only going to impact the black color? I am not able to get how it impacts me in normal day-to-day TV watching.
It won't increase over time. It is only visible in dark scenes in a dark room - not in a bright room.
10
I'm on my 13th TV due to these uniformity issues. I have been changing them for the last three years. Now I'm getting tired of it and was wondering whether these lists of TVs will be updated and carried on, because without you I cannot find out what a TV is really like for uniformity, as people on forums and most reviews say they are fine, when I know hardly any LED TVs have brilliant backlights. I know due to trying all manufacturers top and mid-range TVs with pics to prove how bad the backlight bleed and banding/dse were. They really were absolutely not acceptable, so please carry on your excellent work!
Thanks for the feedback. All LED TVs have this problem, as you mentioned, to various degrees. That is why videophiles and picky customers opt for plasma TVs instead. It is fine for the average customer, but as soon as you start to look for these problems you will find them everywhere.
10
I purchased a Samsung 75" H7150 and while I love the TV, it does have some flashlighting in the corners. I spoke to Samsung and they told me to lower the backlight to 7 and use standard or movie mode and wait 2-3 weeks. It's been a week and the effect is still present in dark scenes, though it is a lot lower than when set to 10. My 30 day return period is almost over and I am wondering if I should try to exchange the set for another one (the same model)? Based on what you said, it looks like waiting three weeks won't help. Samsung said that if the problem does not go away I should respond and have the TV serviced under warranty. Can a service tech do anything for this problem?
It can't really be fixed by a service tech. How bad is the flashlighting? On a 75", you can't really expect perfect uniformity. If it is noticeable with a few lights on with normal footage, then it is a problem and you should exchange it (just don't be too picky, or you will keep exchanging them forever).
8
I just bought a Samsung JU7500 and noticed some pretty severe clouding in the middle of the screen when changing channels and in dark scenes. After gently rubbing the bright areas with a microfiber cloth, the cloudiness is entirely gone. I never would have thought to do that. Thanks!
Glad to hear you got a good result!
7
Is flashlighting normal? It isn't like burn-in, is it?
It is very common. The bigger the TV, the more prone it is to flashlighting. Contrary to burn-in, though, it isn't something that happens over time. If your TV has flashlighting, it will have it since day one and it will stay exactly the same for the rest of its life. It is only affected by physical damage.
3
I have the Sony XBR79X900B, and returned it because of flashlighting/clouding on the top right side of the TV. The TV just looked horrible in a dark room I could even see the blacks it was so bad, so I returned it and got a new set it is a little bit better. But will there always be flashlighting on the model? I was considering paying extra for the Sony XBR75X940C because I heard that full-array backlight has better black uniformity than edge-lit. Is that true?
Every LED TV has some amount of a uniformity issue, but some are worse than others. Full-array TVs are generally better for black uniformity, and the X940C is a higher-end TV, so you would likely have better luck with that.
2
Hi, I bought a Vizio E55", and the bottom right has pretty bad flashlighting. It's annoying with anything that's 2.40:1 because of the black bar that gets lit up right there. Do I return it and try my luck with another TV of the same model? I would just hate to get one that's even worse. Thanks for your time and thoughts on this.
If it's as bad as you say, you might as well. Ours had some clouding, but nothing as bad as that sounds. If you get another bad one, consider buying the Samsung J6200 instead. It should have great black uniformity.
1
I have Sharp Aquos Quattron 60 inch LED smart TV I purchased in 2012 and I just started seeing blinking pixels on the left side, especially on lighter colors. What could the problem mean? I have it under warranty and have a technician coming to look at it. Can the screen be repaired or replaced?
Are the pixels stuck on a single color, or are they actually blinking? If they're stuck, it's possible to fix stuck pixels by putting a very little amount of pressure on the pixel and then turning the TV on and off. This works about 50% of the time. Otherwise, it's likely a board issue, which will mean you'll need a repair.
It's also possible there is an issue with your cable. Be sure that it is securely plugged in at both ends, and try using a different cable to verify that the issue is not that your current one is faulty.
1
Hello, I just got a Vizio M75-C3. I noticed a few brighter spots (4 in center and 1 off to the right) in a totally black image. They are only really noticeable when walking up to the TV and looking down towards it. Head-on, they aren't visible. I am just wondering if it is normal to see worse uniformity at these angles. Obviously, you wouldn't watch anything one foot away looking down at the TV, but I was just curious.
Also, behind one of the spots I have a wall mounted surge protector, is there any way that could cause interference, or is that just a coincidence? Thanks.
Yes, it does make sense. The contrast would weaken at that angle, and so issues with the uniformity would become more apparent.
It's possible that the surge protector could interfere with the TV, but we doubt it's more than coincidence.
If you'd like, you can try gently rubbing the affected areas with a soft cloth to see if you can clear up any of the uniformity issues. This does sometimes help us fix uniformity issues with our TVs.
0
DO LED TVs require a break-in period (e.g. 100 hrs) before achieving an optimal picture? Thank you.
No. They're good to go as soon as you get them.
0
How does the Sharp series UB30U score so high in the black uniformity test when they are edge-lit and not fully backlit?
The UB30U has a direct backlight, and not edge backlighting, so it's not strange that its uniformity is really good. It's also worth noting that edge-lighting has come a long way, and doesn't necessarily mean the uniformity will be bad.
0
How can I get a picture of the white lights in the four corners of my TV? Vizio wants the photos for the warranty. The white spots do not show up on my phone.
If you have an iPhone, try locking the exposure onto a dark object and then taking the picture. If you have an Android phone, increase the exposure from within the camera app's settings. Both of those options should help the phone capture the lighting issues on your TV's screen.
0
I have the same issue of black uniformity, especially when LED LCD TV is been powered, but again I usually discover that the white clouds on the screen clears if the has been in use for more than an hour. Please brother what can you say regarding this? Thanks.
That's unusual. It is possible that when the TV warms up the slightly flexible frame results in better uniformity. You can try to softly massage the problem areas with a microfibre cloth to see if it helps with the issue.
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