Originally Posted by js950
When Sony and Samsung went wide viewing angle, they discovered that using very high zone counts were negated by the dispersion layer so decided to not waste the money. You can argue the value of dispersion vs contrast but that's a choice, not a downgrade.
Precisely this! Off angle viewing of high numbers of local zones was the issue. Think about it a bit, you have a TV panel which has a layer which is creating the color, and behind that layer possibly as much as 1/4 - 1/2 and inch you have the backlight which is then being used to send the light that gets filtered by the LCD panel in front of it to produce the color you then see. This works great if you are sitting directly in front of the TV, everything lines up no problem and having more individual backlights to control ever smaller numbers of pixels from the LCD layer is great as it can allow ever more detailed production of lumen information for the image.
Now, shift the viewing position off angle... All of a sudden, the backlight is no longer behind the pixels you thought it was from this angle because if you move off to the left side of the screen, the backlight that comes through the LCD layer is now off to the right side of the LCD layer, and not the one directly behind the layer. You can try to mitigate this by effectively placing the backlights in mini-cone shaped structures to prevent the off angle viewing from seeing that other LED, however, then you start to run into problems with the display simply looking dimmer as you go off angle since the light it effectively polarized and pointing straight forward out of the display, creating even more of a headache with off angle viewing than you had.
So, the best solution is to do some math to determine based on how far back the LED layer is from the LCD layer, and calculate how far away the next LED can be from any given point based on the viewing angles you want to support such that the LED zone that is controlling the lumen of a pixel is mostly always the one seen no matter that angle used to view that pixel. This results in number of control zones based on how large the TV is and the space between the two layers in the manufacturing. You can increase the number of zones by decreasing the space between the layers.
This is why the mini/micro LED based TV tech is doing. Samsung's "The Wall", and "The Window" have eliminated the gap between the layers by removing the LCD layer entirely and using the LEDs to directly produce the color as well as the light intensity/lumen. TCL's vidrian tech (what they are naming mini-LED) removed much of the gap between the LED and LCD layers. This is what will let you have more hardware backlight zones. Without that, more zones results in a worse display since you are in many cases having pixels that are attempting to be bright white, but the LED backlight providing the light through that pixel to the viewing angle you are looking at it from may be off entirely because it is trying to show the black darkness of space while the white pixel next to it might be showing a star, and in the end all you see a dark gray bloom and black, with no stars...
P.S. This is why I have been so pissed that it is taking so long for micro LED TVs to hit the market. I get it that a lot happened in the last 4 years that they have been demo'ing it and probably 7 years that they have been developing it. We went from 1080p to 8k during that time, which meant that the number of LEDs in the TV expanded at a staggering pace meaning the size of the LED needed to decrease dramatically and requiring the manufacturing defects per LED to be reduced drastically as well (since there are now more LEDs required to produce a panel, if the defects per LED did not decrease, the number of defective panels would increase by a proportional value as to the number of additional LEDs in the the case of just going from 1080p to 4k, that would be a 16x change). Again, I get why it is taking so long, but I still just wish we we see a true consumer class TV and not just the commercial class advertising displays that have been produced.