A TFT screen works on a completely different principle then CRT's. In TFT display, there is a fluorescent back light which shines light through a layer of liquid crystals. TFT screens work on the same principles of light, there are still 3 separate sub pixels which each display one primary colour. An image is formed by the liquids ability to block light when it is charged with a current. Every TFT flat panel screen screen is made through a process called photolithography. This process will engrave small transistors on the sheet of glass, and each one can be ditigally controlled. Behind this transistor sheet is a powerful flourescent light. In front of this sheet of transistors is a thin film of liquid that is less than 1/100th of a millimeter thick. In front of that is a protective sheet of glass which is the screen. How it works is the liquid's crystal molecules will align differently under electrical current. When no electrical current is applied, all of the back light is allowed to pass through the liquid layer. When the transistor has a charge, the liquid molecules begin to align in such a way that they will block all light from passing through. Depending on the charge of the transistor, different light intensities can be made.

The benifits of a TFT flat panel are that they consume less energy, have lower radiation, and have a brighter picture than CRT's. Also TFT's are lighter, thin, and do not suffer any geometric distortion because they are perfectly flat. The downside to flat panels are that they have a fixed native resolution. This means that all other resolutions have to be scaled up to be displayed, which can result in some jazzed distortion due to interpolation. Another downside to them is that they have a limited colour range. Some really bright whites, and really dark darks are almost impossible to display because of the liquid's sensitivity. This means that anything over 16-bit colour will not be displayed. They can also suffer from broken transistors, meaning that some pixels may not work. This will only be noticeable in some situations, but finding a perfect display may take a little effort. Because TFT's are inherently digitally operated, it is unnecessary to convert to an analog picture like for a CRT. The better TFT displays have a digital video connection, which can be plugged into some video cards, called a DVI. This is to prevent image quality loss through the analog to digital to analog conversion that the signal goes through.

Current TFT displays have poorer quality than CRT's, and so they have only being used in situations where size is more important than quality. Laptops and hand held devices use TFT screens rather than CRT, because they screens can be manufactured to be almost completely flat, while CRT will always require a large foot print. As manufacturing techniques improve, LCD image quality is starting to improve and is getting very competitive to CRT's. The advantages of flat panels over CRT's are that they can be smaller, lighter in weight, have a brighter picture, and consume less energy. The current down sides are poorer image quality, fixed resolution, smaller screen size, slower refresh rate, limited colour range and cost. The materials to produce TFT's are less expensive than CRT's, but manufactures are still refining the manufacturing process, and are still having difficulty in production, meaning higher prices.

CRTs | Masking | TFT Flat Panels