The subpixels in an LCD screen use liquid crystal molecules that act as light pathways and also as dimmer switches to let the backlight through, partially through or not at all to reach red, green and blue filters. For more on the red, green and blue concept, see RGB
When unenergized, the liquid crystals start out looking like twisted ladders because they orient themselves to microscopic grooves, called "rubbings," in top and bottom glass panels, and the rubbings are at right angles to each other. When energized by electrodes at the top and bottom, they re-orient themselves away from the orientation of the front polarizer panel, and the more they twist away, the less light reaches the color filters, which create the red, green and blue lights.
Up to 240 Changes Per Second
In an LCD HDTV set, the subpixels can change their state up to 60 times per second. In a 3D TV or computer monitor, it can be up to 120 times per second, and in a 240 Hz TV, up to 240 times per second. See LCD
and LCD example
Unenergized, the liquid crystal rods orient themselves to the rubbings in front and rear glass panels, which is why they look like twisted ladders. In this state, they allow light to pass from the backlight to the color filters, and red, green and blue at full and equal intensities create white (see RGB
). In a 4K TV, there are eight million of these three-segment pixels (24 million crystal paths).
When energized by transparent electrodes (not shown) at the top and bottom, the crystals orient themselves away from the front polarizer, allowing less light to pass through the color filters. In this example, gray is produced when the red, green and blue light is at equal but lower intensities.
TN Vs. IPS
The liquid crystals in the ubiquitous twisted nematic (TN) display become more perpendicular to the top panels when energized. In an "in-plane switching" (IPS) display, they remain on the same plane as the panels. See IPS panel