Summary
LED is a new technology in TVs and Computer Monitors and distinctly different from LCD or TFT. LCD requires a backlight, LED does not. LCD uses silicon-based devices, LED uses organic plastic-based devices. LCD has low contrast, LED has very high contrast. LCD is now very old technology and will be replaced by the new organic LED quite quickly over next few years.
Analysis
Liquid Crystal Display (LCD) technology has been around for many years since it was first commonly used in digital wrist watches. It requires a back-light of some form and operates by blocking that light (generally white light) in some way so as to darken it in colour or turn it black (e.g. block out the back-light entirely). The most common form of LCD today uses TFT technology as the active mechanism and is used in the majority of flat screen TVs and computer monitors from small photograph size to 60+ inches diagonal. Small postage stamp sized LCD units are used in some digital projectors for the presentation and home cinema markets (e.g. Sanyo, Epson, Dell).
In older flat screens, the back light used a flourescent tube to illuminate the panel. However in new laptop screens, white-light LED technology is used to provide the back-light as it consumes less power and therefore prolongs the battery usage time of the laptop.
Whilst LCD technology is mature, it has one drawback in it's principal method of operation – in that it seeks to block an existing light source. It has very good colour reproduction and balance (e.g. good for TV and movies) but because of its mode of operation it has very low contrast (generally 600:1 or less).
Some 15 years ago, some scientists at Cambridge University in the UK began experimenting with high voltages and plastic insulation materials. They discovered that depending on the composition of the plastics, some of them glowed and in different colours. They pursued this research further to create Organic Light Emitting Devices or OLEDs. Initially the technology was used on small devices and for car dashboard displays, but has now sufficiently matured to make screens of usable size for use as TVs or computer monitors. The OLED technology is different from the standard Light Emitting Diode (LED) that is used in very large outdoor display systems (as used in stadia) or devices such as have entered the market in recent years for very low power visible lighting. These use silicon-based compounds in their manufacture whereas OLED use organic-based plastic compounds and consequently the manufacturing processes are quite different.
Unlike an LCD, OLEDs do not block light from the back of the screen, they actually generate the light needed on an individual pixel by pixel basis, and in the right combination of colours. This results in lower power requirement as light is produced only where it is needed, as it is needed. The light level can be controlled from nothing to full brightness, meaning contrast ratios are very high (typically 1000000:1). The colour composition is generally good and having matured as a technology will match that of TFT LCDs. Because there is no need for a backlight, the OLED technology produces a very thin screen (1-2 millimetres as opposed to 8 millimetres or more) and this is being used as a marketing tool particularly by TV screen manufacturers (especially Sony).
However, as LCD technology has been around much longer, there is massive investment in production facilities and the cost per unit is therefore very low. Whilst OLED technology is now scaling up in size for use in the larger devices, it is not produced in huge quantity yet, thus the price per unit is currently at a premium compared to LCD. However, the manufacturing process is understood to be simpler and therefore once manufacturing quantities reach the appropriate level start to produce lower unit costs than is possible using LCD. It is therefore only a matter of time before OLEDs completely replace LCD technology in the marketplace.
