If you are buying a new TV, you may find terms like “dimming zones” or “full range local dimming” in marketing materials. Understanding what this means and how it relates to image quality can help you make a better purchasing decision.
Backlight and dimming zones
There are two types of displays that are dominating the market at the moment, LCD displays with LED lighting and self-emitting OLED displays. Since OLED equipment does not have a backlight, local dimming only applies to LED-illuminated LCD equipment. Full-matrix local dimming means that zones can be adjusted independently on screen instead of edge-lit dimming that can only be dimmed in horizontal bands.
Dimming zones reduce the intensity of the backlight in specific areas of the screen to improve the contrast ratio. This is necessary because LCD televisions rely on a backlight to shine through the stack of screens to create an image on the screen. To display black, this backlight must be effectively blocked, which can make black appear gray.
Since contrast ratio is one of the most important factors determining image quality, reducing backlight can improve contrast ratio by making blacks blacker. More areas mean more control over the image displayed on the screen.
Manufacturers refer to dimming zones differently in their marketing materials. Look for words like “local zones” or “contrast control zones” and keep in mind that larger screen sizes may have more zones than smaller ones, even on the same TV model.
Full-array local dimming is no longer primarily reserved for high-end LED arrays, and inexpensive manufacturers offer the function as standard on cheaper models such as the TCL 5 Series.
Economical with local dimming
Understanding the limitations of local dimming
The attenuation zones are not perfect and there is a limit to how effective they are. For example, in a scene with both light and dark elements, you may be able to see the edge of a dimming area due to “ghosting,” where the backlight raises dark areas of the screen in a distracting way.
At the same time, in a predominantly dark scene, you may experience a black crush, where the dimming causes a loss in shadow detail or subtle reflections. A good example of this is a star field test, where the stars disappear because the dimming algorithm does not consider them bright enough to activate the backlight.
Since the attenuation is dependent on the processor inside the TV, the feature can introduce latency. This is not a problem when watching movies or television, but it can be a problem when playing games. For this reason, some televisions disable or degrade their dimming capabilities while in gaming mode.
This can result in a worse contrast ratio, where blacks appear high. It won’t be as noticeable in a bright room, but if you’re gaming in the dark, you might want to go for an OLED screen instead.
Local dimming does not apply to OLED
If you are thinking of buying an OLED TV, you don’t have to worry about local dimming zones. Since OLED is self-emitting, each pixel is capable of generating its own light output. There is no need to dim the backlight because there is no backlight.
Learn more about the difference between OLED and LCD with LED lighting in our guide to buying a TV.