Television sets use to be bulky, heavy and energy consuming before the advent of the Liquid Crystal Display (LCD) technology. LCD TVs are slim, lightweight and can be hung on walls. TVs are much like laptops now with flat screens.
This is made possible with the adoption of the LCD display technology that has long been used on our digital watches and calculators.
The Uniqueness Of Liquid Crystals
Liquid crystals are substances that fall between a solid and liquid material. It can be described to be an extension of the three states of matter because it is not any of those three. Just like states of matter, it can be in any of the two states it is commonly found with.
The Nematic phase is the state where it is more in the liquid state, where molecules move freely past each other along the same direction. The Smectic phase is when the liquid crystals are cooled. The molecules here form layers that are capable of sliding past each other.
The Working Principle Of LCD
LCD displays are implemented by utilizing the power of liquid crystals and polarized light. The images or pictures displayed on the LCD TV screen results from millions of pixels. Each pixel is a unique red, green or blue light that is switched OFF or ON to produce the picture that is seen in front of the screen.
In addition to plasma screen mode of operation, in LCD screens, the pixels get switched off or on electronically by using liquid crystals which rotates polarized light.
Applying electricity to Nematic liquid crystal straightens it out from its initial twisted-up form. This is the switching on and off process.
Polarised Light And Liquid Crystal And Composition Of The Technique
LCD screens work on a principle where the backlight is required for image display on the screen. At the back of the screen, there is a bright light which shines toward the viewer. At the front of this are the millions of pixels and sub-pixels colored blue, red and green. All pixels have polarizing glass filter at the back and another in front at 90-degrees. This makes the pixels to always appear dark.
In the midst of the two polarizing filters is the minute twisted nematic liquid crystal that untwists and twists (On and Off) through electronic means.
Switching Off And On
When the nematic crystals are switched off, light passing through it is rotated at 90 degrees, giving way for light to flow pass the two polarizing filters. This makes the pixel brighter. On switching on the crystal, it does not rotate the light that is blocked by one of the two polarizers. Here the pixel appears dark.
Each of the pixels is controlled separately by a transistor that is capable of switching it off or on several times per second.
Switching On Procedure
- The backlight of the screen shines
- Apart from vibrating horizontal light waves, all other light waves are blocked by the horizontal polarizing filter in front of the shining light.
- Only horizontally vibrating light waves get through.
- The transistor switches on the pixel when electricity flow in the liquid crystal is switched off. This results in a twisted crystal. The resulting twisted crystal rotates by 90 degrees the light waves as they go past it.
- The horizontally vibrating light waves that pass through the crystal come out vibrating horizontally.
- All light waves are blocked by vertically polarizing filter except the ones vibrating vertically. The vibrating vertical light is now able to pass through vertical filters.
- The pixel brightens up. The blue, red or green filters give the color of the pixel.