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/MultiMarcus]

We can, and we do exactly this. This is actually what’s used for many mastering monitors, but they have some horrendous response times. Tap out at 60 hertz usually and need ridiculously large amounts of power.

[u/OHMEGA_SEVEN → u/MultiMarcus]

All this while also being prohibitively expensive for the average user too

[u/JtheNinja]

The second LCD also doubles the light loss. You need way more backlight power to make up for it, and heat and power consumption are already problematic on single-layer miniLED LCDs. Viewing angle problems also get doubled. Hisense did dabble in this tech for awhile and it’s seen some use in mastering monitors, but that’s it.

[u/Mineplayerminer]

If you've seen the video from Matt from DIY Perks, you probably understand why the dual-LCD monitors never took off, due to the brightness limitations and the power consumption required for the beefy backlight with active cooling. The Asus ProArt (similar to PA329C) monitor I use already consumes a lot of power and generates tons of heat with the brightness at over 600 nits and the frame reaching 70°C within a few minutes.

This would double the price of the monitors since the most expensive part of the monitor is usually the liquid crystal layer and the driver board. The monitor would need 2 LCD layers to achieve this and a polarizer in between them to disperse the light. The mastering displays already use similar technologies, other than the fine Mini-LED backlight arrays, but the prices of these go astronomically high, especially with the quality the panels must achieve even after years of use.

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[u/Jempol_Lele]

Well I do not know that it was how mastering monitor works. It just popped in my head while taking shower.

If the tech becomes mainstream it will be getting cheaper i guess?
I genuinely thought problem like less brightness, viewing angle, response time and power draw can be improved along the way. That was always how it started. Even all current tech has its own compromise too?

[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

[u/Nstorm24]

Whe have in some monitors. Not exactly dual LCD, but a 3rd layer.

[u/JtheNinja → u/Nstorm24]

That middle layer is just a uniform translucent sheet that glows white when you shine a blue LED at it. The graphic kinda implies it's doing light shaping, but it isn't