High-Death wrote:
I still think there is some confusion, you are only describing the polarization of the sub-pixels/pixels. They are twisted and remain in this polarized form for an unknown reason letting the light pass. That is obviously required for the light to pass and an image be generated. But you are assuming that PWM and the shades gradations all the depends on the twisted design os the pixels, for each voltage a certain twist and a certain amount of light would pass. And in this case the LEDs would have just two configurations, ON and OFF. Do I read you right?
The problem with this design is that the twists are too slow, I believe they usually take at least 2ms to return to the normal state of total blocking of light and the phosphor will take no more than 1ms to be lit and go off. It is also more efficient to modulate the intensity of the phosphor luminosity for temporal dithering then the twists of the pixels. And this brings me to an apparent contradiction in the twists-for-shades theory, since the pixels will have to change their configuration a few times in just one second to generate a proper shading how come a "state memory" would develop leaving the pixel persistently stuck in the same position?
In the first paragraph you correctly summarized: the amount of twist is a function of voltage, so you can achieve different degrees of brightness of a pixel using different voltages applied to the crystals.
In the second paragraph you deviate from this explanation and assume that you have to change the crystal configurations "a few times in just one second to generate a proper shading". I don't know where this came from. All that the display has to do is to supply the appropriate voltage for the desired twist of the crystals to produce the required transmissivity of light, and then the crystal's orientation remains fixed and doesn't change until a new color is to be displayed.
One thing I have glossed over here is that what actually happens is that a certain percentage of the crystals will twist fully at a certain voltage, resulting in an overall transmissivity that is dependent on the voltage. An individual crystal either twists fully or not at all, and the opacity is a function of what percentage of crystals twist at a given voltage (even this is probably a simplification as I can't believe that every single crystal always twists 100% one way or the other, and there is never any stuck in an intermediate state, but in any case the effect is the same: the opacity is a function of the voltage, which produces a steady state orientation of the crystals).
Here is an excerpt from Wikipedia's article on "Twisted Nematic Field Effect":
"The amount of opacity can be controlled by varying the voltage. At voltages near the threshold, only some of the crystals will re-align, and the display will be partially transparent. As the voltage is increased, more of the crystals will re-align until it becomes completely "switched". A voltage of about 1 V is required to make the crystal align itself with the field, and no current passes through the crystal itself. Thus the electrical power required for that action is very low."
High-Death wrote:
Now the way I am considering the LEDs are the the ones submitted to modulation and changes in luminosity while the twists are either on or off only.
To reiterate, the twists for any given crystal are either on or off only; but of course each cell (subpixel) is made up of millions (billions?) of crystals and the overall opacity is a function of how many have twisted one way vs the other. There is no need for temporal modulation to produce an effective opacity. The static orientation of the crystals is enough. And it's a divergence of the static orientation from what it is supposed to be, due to lingering voltages or some other effect that is causing the image retention.