LCD televisions do not ‘create’ light themselves. Rather, this is the work of the backlight, an illumination that produces the image that you see.
This is in contrast (no pun intended) to older televisions, which is apparent in both the fact that pictures now are much sharper and at the same time, the blacks of the screen can at times come across as quite gray.
What Is Local Dimming?
Local dimming is a feature and a way of making visuals on an LCD TV much more realistic. Specifically, it takes the dark grays closer to their true black value. Everything looks much richer, the whole picture is accentuated to perfection, and darker images and scenes come across as much more realistic.
This is achieved by “locally” dimming the backlight wherever the blacks are being displayed. “TV local dimming” makes the contrast ratio better (higher, in other words) so that the parts that don’t need dimming are to remain unaffected.
Of course, this problem does not arise in OLED and MicroLED displays, particularly the best 75-80” ones. This is because OLEDs use self-emitting pixels as opposed to a backlight. These pixels go dark or light themselves up completely individually, meaning the black is truly black and otherwise.
However, even for those who own an LCD TV, local dimming is a dynamic “fix” to the problem.
Full-Array Local Dimming
Something you’ll notice about the best 4K TVs is that they support FALD or Full Array Local Dimming. You’ll also see it called direct backlighting or direct-lit local dimming.
This is generally understood to be the superior type of local dimming, as well as the most expensive and physically hefty, where the LEDs are placed all over the backlight panel.
By understanding FALD, we can also understand the other types as well as local dimming zones very easily. Full array arranges for many small local dimming zones, in the forms of lights – hundreds of them – all individually dimmed. This results in highly accurate, highly well-done dimming where the brightness and darkness both operate at 100%.
Of course, utilizing FALD also means that more space is needed (hence the ‘hefty’ declaration).
The Local Dimming Zones
The zones mentioned earlier are essentially groupings of these LED arrays.
It’s the local dimming zones that determine how effectively or precisely your TV utilizes local dimming. Smaller zones help in reducing any bleeding through of light to portions where it doesn’t need to be, whereas larger zones (which would naturally be fewer), take over bigger portions of the visual, with a lot of light spilling over where it shouldn’t be meaning that local dimming is not completely effective – perhaps to the point of being counterproductive.
However, the responsiveness of the zones also matters. In some cases, you can observe a lag where zones light up and go dim after the “scene” no longer calls for the specific situation, leaving a little bit of a ghost image in your eyes for a split second or longer.
While Full Array Local Dimming utilizes lots of small lights (meaning hundreds of zones), the other forms are not so sharp.
Edge-Lit and Back-Lit Local Dimming
Edge-lit local dimming only uses LEDs across the edges of the screen (say the top and the bottom) and from there administer the lighting for the whole screen.
This is perhaps the most common form of dimming, also very prevalent in smartphones, but of course, while it allows the products to remain “slim” and lightweight, there’s a lot of noticeable glow from the edges from where the LEDs try to illuminate the whole of the screen, both edges needing to reach the center.
Back-lit TV local dimming, while closer to full array in terms of the LEDs being spread across the screen, only uses a limited number of lamps – usually with only four to 12 zones that fluctuate in brightness simultaneously. This results in deeper blacks but also dims areas that might need brighter light.
UHD Dimming VS Local Dimming
Finally, we have a “newer” technology as well. UHD dimming is a form of local dimming, developed and used exclusively by Samsung for their QDOT (quantum dot) television sets.
UHD dimming focuses on the strength of the contrast ratio and utilizes both a wider array of more fine dimming zones with powerful algorithms that create a much more refined level of TV local dimming.
Thanks, Uneeb. You made it quickly clear how these various dimming systems work.