How a LCD TV Works

Because the light source is a bulb at the back of the screen, rather than light-emitting phosphors at the front of the screen, this technology is referred to as 'transmissive'.

Liquid crystals are familiar technology. We have used them on wristwatches and calculator screens for decades. The technology was originally adapted for high-quality displays in computers and now it is a commonly used for home entertainment.

If an electrical current is applied to the liquid crystal, it will untwist, effectively blocking out the light. Different strengths of current result in more or less of the light being blocked, so different shades of light become possible.

If this principle is multiplied many times you get a basic LCD screen. Early applications used a 'passive matrix' display, where a grid of conductors lies alongside the LCD pixels. This allows individual pixels to be switched on and off, but also introduced blurring to the image because some electrical current would find its way into neighbouring pixels.

The development of 'active matrix' LCDs, using thin film transistors (TFTs) was critical in bringing LCD displays up to the necessary specification for TV usage.

TFTs are best viewed as very small switching transistors and capacitors. The transistors act as switches, enabling the activation of pixels with no effect on neighbouring pixels in an LCD screen. The capacitors are able to store the charge, maintaining voltage for one frame scan. With each pixel having its own dedicated transistor and capacitor it is possible to target individual pixels with complete accuracy.

Control over the strength of the current applied also brings a workable greyscale into the equation. A weaker current causes the liquid crystals to unbend to a lesser degree, blocking out only part of the light source - in this way it is possible to achieve 256 shades. The addition of a colour filter layer, and the division of each LCD pixel into three sub-pixels (red, green and blue) means that 256 x 256 x 256 combinations are possible, giving the familiar colour palette of 16.7 million colours.

TFT technology also greatly improves the response time of the individual pixels. Where passive matrix configurations are only suitable for basic displays, active matrix displays can handle fast-moving video with minimal blurring, making home cinema applications possible.