By: John Michael Pierobon
Flat panel displays are becoming more and more popular in the office and in the home. This article explains how flat panel displays work and why they are so popular.
There are several ways of achieving a flat panel display including an alphabet soup of three-letter acronyms, but the leading technologies of today are Liquid Crystal Display (LCD), and gas plasma display panels.
As its name implies, an LCD contains transparent organic polymers which flow like liquids, but maintain a short range crystalline order. The liquid crystal material is sealed between two flat glass plates or quartz substrates, each of which has a polarizer on its outer edge and a matrix of transparent indium tin oxide electrodes on the inner surfaces.
The liquid crystal polymer responds to an applied voltage, which is controlled by the matrix of transparent indium tin oxide electrodes. When no voltage is applied, the polarizers on the front and back of the display are oriented at 90° from one another. With this orientation no light can pass through, unless the polarization of the light is altered.
All LCD have a source of reflected or back lighting. The liquid crystals act as a shutter. When voltage is applied, they rotate to allow light to pass through the front polarizer, thus illuminating the screen.
For color LCD, each pixel must consist of three adjoining cells, each containing a red, green, or blue filter. Red, green, and blue are the primary colors of light.
Passive matrix and active matrix are two kinds of LCD.
Passive matrix LCD are relatively easy to manufacture and have been around since pocket calculators were invented. Passive matrix LCD have a transparent, horizontal metal electrodes on one glass plate and vertical metal electrodes on the other plate. Voltages on the row and column electrodes combine at a cross point to light a given pixel. Passive matrix LCD are slow, and do not have as nice of a display as active matrix LCD.
Active matrix LCD are fabricated similar to an integrated circuit board, with the rear glass containing a matrix of one for monochrome, or three for color, thin film transistors (TFT) per pixel. Virtually every laptop sold today has an active matrix LCD.
Because of manufacturing constraints, very large active matrix LCD is not a serious contender for achieving a flat panel display on very large screens. Enter gas plasma display technology, which acts like as a collection of very small neon bulbs.
Gas plasma display technology is similar to LCD technology. Instead of using liquid crystals, a gas mixture of neon and xenon is squeezed between two sealed glass plates with electrodes deposited on their surfaces. The plates are sealed so that the electrodes form right angles, similar to passive matrix LCD. When voltage is applied at an intersection of two electrodes, the gas breaks down and produces weakly ionized plasma, which emits ultraviolet radiation. The ultraviolet radiation reacts with phosphors in each sub-pixel to produce colored light (red, green, or blue). These phosphors are the same as used in Cathode Ray Tube (CRT) monitors and televisions.
Flat panel displays are becoming popular for many reasons including size, looks, and price.
A CRT needs depth to project an image, and it is what makes computer monitors and televisions so big and bulky. By contrast, a flat panel display is flat. It is only four to six inches deep.
As people begin to demand bigger television and computer screens, the need for flat panel displays increases because people do not want to give up valuable desktop space or living room space. A flat panel display takes up only about one-sixth the depth of a CRT.
Although gas plasma displays consume more power and generate more heat than an LCD, both are still more energy efficient than a CRT.
Studies have shown that LCD displays improve reading speed, because the screen resolution is better. Color display is also sharper. A flat panel display can display up to 16,777,216 different colors.
In addition to crisp, bright images, there are other advantages. Unlike projection screens, which are designed to concentrate reflection to a narrow viewing area for brightness, plasma screens permit an exceptionally broad viewing angle of 160°. Thus, no matter where audience members are in the room, the brightness and clarity come through. Since panels are backlit rather than reflective, they perform exceptionally well in bright environments. And because the panels are absolutely flat, glare is reduced and viewers can see the entire screen from a broader perspective.
Large screen gas plasma displays support both 4:3 and 16:9 aspect ratios, which are compatible with High Definition TeleVision (HDTV). The FCC has mandated that by 2009 all television stations in the United States will broadcast only in HDTV. Analog television is being phased out and prices of flat panel displays are falling. So, the world is becoming flat.