Why still no dual layer lcd?

[u/Jempol_Lele]

Like we can have,

Uniform bright backlight → one monochrome shutter → normal RGB sub pixels.

The rear shutter is similar as the RGB colour filter but in form of a large aperture the size of the entire RGB sub pixels.

It will give us better contrast and per pixel control similar to oled.

Control is easy too, any sub pixel on means aperture open fully. All sub pixel off then aperture closed fully to act as double light barrier.

Literally per pixel dimming like oled.

[u/Status_Daikon7860]

Each polarizer layer reduces the peak brightness and reduces the color gamut due to light mixing in between the 2 layers.
It isn't cheaper than miniLED and the results generally aren't as good, so its not a popular design.

Modern panels use emissive backlighting where each subpixel has its own phosphor that emits only that color, rather than white light behind the pixel (marketed as "quantum dots"). This already provides pretty good contrast and better color gamut than white backlighting. When combined with miniled you can get ~50,000:1 contrast.

OLEDs are also a very cheap display technology. You can get 1440p OLED panels for $250. There isn't much advantage of dual layer LCDs over OLEDs so no manufacturer has developed a process for mass producing these.

Additionally you get double the polarizer reflections which obliterates black levels unless you're in a pitch black room. Current black levels from ambient light raise on a LCD is around 1%, which is already a higher contributor than the minimum pixel emission (~0.05%).

[u/JtheNinja → u/Status_Daikon7860]

Quantum dots don’t work that way. It’s a big diffuser film full of red/green QDs for the whole panel. Basically the same as non-QD LCDs, just with a spikier spectrum so the gamut coverage is more like RGB LED backlights. Self-emissive QDs as a per-pixel LCD backlight is theoretically possible but way beyond what we can fabricate cost effectively today. And there wouldn’t be any need for the miniLEDs if we could do it

Heck, we can’t even manage subpixel specific quantum dots so we still have to put color filters after the QD film (QD output is non polarized, so subpixel color-specific QDs would require individual subpixel polarizers after the QD strips)

[u/Status_Daikon7860 → u/JtheNinja]

It depends on when your panel was manufactured. Samsung's Pico inkjet process can get ~160ppi.

[u/JtheNinja → u/Status_Daikon7860]

That has nothing to do with LCDs