Black Uniformity of TVs

Clouding and Flashlighting

Additional information

VA vs. IPS panels

LED-backlit LCD TVs typically come in one of two sub-types of panels: Vertical Alignment (VA) or In-Plane Switching (IPS). VA panels tend to have much high contrast ratios, and therefore better black uniformity. IPS panels, on the other hand, have worse contrast ratios and suffer from more backlight issues that can affect black uniformity, including 'IPS glow', which is a kind of 'glow' effect that can be seen in the corners of IPS screens.

Learn more about the difference between VA and IPS

LED vs. OLED black uniformity

LED-backlit LCD TVs are prone to black uniformity issues, but OLED TVs can produce virtually perfect blacks because their pixels are self-emitting, and therefore don't have the same limitations caused by improper backlight implementation. That means they don't suffer from clouding or flashlighting as LED TVs do.

Learn more about the difference between OLED and LED TVs

The cause of flashlighting and clouding

Flashlighting and clouding can occur for a few reasons:

• Poorly designed backlight placement. The type of backlight and its position directly affects the uniformity of the screen. The worst uniformity can be found on 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. 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 lighting intensity. 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 the flashlighting is caused by pressure from the TV's frame, you can adjust it by slightly loosening or tightening the screws behind the edge of the screen. Some TVs don't expose the screws, however, so this won't always be possible. 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. While this can fix the issue, we don't recommend it unless you know exactly what you're doing, as it may cause more problems than it solves. 

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, although you should be very careful to avoid damaging your screen.

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 uniformity issues than others because of slight variation in the manufacturing or shipping process. It can be worth trying to exchange it for the same model before going with an entirely different TV. 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.
• Local dimming, if the TV is equipped with it, can also help. You can learn more about local dimming 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 (in the case of a big temperature swing, for instance, 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

Black uniformity refers to how evenly a TV can display black across the screen, especially when displaying a bright object over a dark background. 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 to capture the black uniformity, and then we calculate the color values of the pixels to find the standard deviation of the uniformity. We then do the same with local dimming enabled.

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 the 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. In the end, the safest bet may be to simply return or exchange your TV if you can, since uniformity varies between individual units.