LCD - Liquid Crystal Display
- A liquid crystal display consists of two glass plates each containing a light polarizer. One glass plate contains vertical polarizer and the other plate having horizontal polarizer.
- Horizontal polarizer acts as a filter, allowing only the horizontal component of light to pass through and vertical polarizer allows only the vertical component of light to pass through.
- Rows of horizontal conductors on one glass plate and columns of vertical conductors on the other glass plate are built in to address individual pixels. The intersection of these rows and columns define the pixel grid. The conductors are transparent.
- A liquid crystal layer exists between the two glass plates. The liquid crystal means a compound which has crystalline structure of its molecules, yet it flows like a liquid.
- Ambient light is captured at one glass plate, vertically polarized and then is rotated (phase of the light wave changed) to horizontal polarity during the period it passes through the liquid crystal layer. Then it passes through the horizontal filter. Light is then reflected back through all the layers to the viewer, giving an appearance of lightness.
- However, if the liquid crystal molecules are charged, they become aligned and no longer allow the light to change its polarity when the light passes through them. If this occurs, no light can pass through the horizontal filter, so the screen appears dark. To do this we simply apply voltage between two intersecting conductors residing in two glass plates.
- Crystals can be dyed to provide color.
- Screen is refreshed at a rate of 60 frames per seconds using a refresh buffer. An LCD may be backlit, so as not to be dependent on ambient light. This is known as passive matrix LCD. However, ambient light is rarely used now a days.
- Most of the LCD are manufactured using active matrix LCD. In active matrix LCD, transistors are placed at every pixel location to control voltage and to prevent charge from gradually leaking out from the liquid crystal cells.
- TFT (thin film transistor) is most popular LCD technology today.