Basic Principle

1. Offline (no voltage is applied)

Molecules movement

• Along the upper plate : Point in direction 'a'



• Along the lower plate : Point in direction 'b‘
  


• Forcing the liquid crystals into a twisted structural arrangement. (Resultant force)

Light movement

• Light travels through the spacing of the molecular arrangement.
  
• The light also "twists" as it passes through the twisted liquid crystals.


• Light bends 90 degrees as it follows the twist of the molecules.


• Polarized light pass through the analyzer (lower polarizer).
  
  

2. Online (voltage is applied)

Molecules movement

• Liquid crystal molecules straighten out of their helix pattern


• Molecules rearrange themselves vertically (Along with the electric field)


• No twisting thoughout the movement


• Forcing the liquid crystals into a straight structural arrangement. (Electric force)

Light movement

• Twisted light passes straight through.


• Light passes straight through along the arrangement of molecules.
• Polarized light cannot pass through the lower analyzer (lower polarizer).


• Screen darkens.

Sequences of offline and online mode

Offline

1. Surrounding light is polarized on the upper plate.


2. Light moves along with liquid crystals and twisted at right angle.


3. Molecules and lights are parallel to the lower analyzer.


4. Light passes through the plate.


5. Screen appear transparent.

Online

1. Surrounding light is polarized on the upper plate.


2. Light moves along with liquid crystals which moves straight along the electric field.


3. Molecules and lights are perpendicular to the lower analyzer.


4. Light cannot pass through the plate.
5. Screen appear dark.

Physical principle

Liquid crystals are neither a pure solid nor a pure liquid, but rather a hybrid of both. One particular variety of interest is the twisted nematic liquid crystal whose molecules have a natural tendency to assume a twisted spiral structure when the material is sandwiched between finely grooved glass substrates with orthogonal orientation. Note that the molecules in contact with the grooved surfaces align themselves in parallel along the grooves. The molecular spiral causes the crystal to behave like a wave polarizer; unpolarized light incident upon the entrance substrate follows the orientation of the spiral, emerging through the exit substrate with its polarization (direction of electric field) parallel to the groove’s direction.