How do TN and IPS LCDs produce grays?

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SUMMARY

This discussion focuses on the mechanisms by which TN (Twisted Nematic) and IPS (In-Plane Switching) LCDs produce gray shades through varying liquid crystal orientations. In TN cells, certain sections of the liquid crystals can complete a 90-degree twist while others remain perpendicular, affecting brightness levels. IPS cells utilize a range of angles, such as 30, 60, or 80 degrees, as the crystals transition towards a 90-degree orientation. Additionally, Pulse Width Modulation (PWM) is employed to simulate gray shades by rapidly toggling the display on and off, creating the illusion of varying brightness to the human eye.

PREREQUISITES
  • Understanding of liquid crystal display (LCD) technology
  • Knowledge of TN and IPS panel structures
  • Familiarity with Pulse Width Modulation (PWM) techniques
  • Basic principles of light polarization
NEXT STEPS
  • Research the differences in liquid crystal alignment between TN and IPS displays
  • Explore the effects of PWM on perceived brightness in LCDs
  • Learn about the impact of viewing angles on color accuracy in IPS panels
  • Investigate advanced LCD technologies such as OLED and Mini-LED
USEFUL FOR

Display engineers, electronics enthusiasts, and anyone interested in the technical workings of LCD technologies and their color reproduction methods.

SIM677
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I have the general idea of how these work when they're on or off, but I'm less clear about what's going on when they're only receiving partial voltages on the level of the liquid crystals.

For a TN cell, are some sections completing the 90 degree turn while others have crystals oriented to be perpendicular to the screen? For an IPS cell, are the liquid crystals being angled at say 30, 60 or 80 degrees on their way to 90 degrees? Or is there variation and it all just averages out to a decreased brightness?
 
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I'm not sure about this particular application, but many use PWM control to make it APPEAR gray to the human eye by turning on and off very quickly.

Anyhow, Welcome to PF, and maybe someone else will have specific information :)
 

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