Flat panel displays are thin, flat electronic devices used for displaying alphanumeric information, graphics, and images. The dominant technologies are LCDs, plasma displays and electroluminescent displays. A Liquid Crystal Display (LCD) utilizes two sheets of polarizing material with a liquid crystal solution between them. When an electric current is passed through the liquid it causes the crystals to align so that light cannot pass through them. Each crystal acts as a shutter, either allowing light to pass through or blocking the light. In a plasma display, a gas fills the spaces between two glass sheets that are lined up in parallel separated by a gap just 100 to 200 microns wide. Discharging this gas using electrodes generates UV light. Red, green, and blue fluorescent substances absorb these UV discharges and then re-radiate the energy as visible light to produce the colors that appear on the screen. An ELD works by sandwiching a thin film of phosphorescent substance between two plates. One plate is coated with vertical wires and the other with horizontal wires, forming a grid. When an electrical current is passed through a horizontal and vertical wire, the phosphorescent film at the intersection glows, creating a point of light or pixel. EL Displays, being an emissive technology (rather than shuttering a light source as per LCDs) are most useful in applications where high visibility in all light conditions is essential.
LCDs are the most common type of flat panel displays available on the market. LCDs have specific matrix types associated with them that do not necessarily apply to the other types of flat panel displays. These include PMLDD and AMLCD. Passive matrix LCDs (PMLCDs) are the most common flat panel display. PMLCDs have closely spaced, transparent, horizontal metal electrodes on one-glass plate and vertical electrodes on the other plate. Voltages on these row and column electrodes combine at a cross point to turn on the pixel at that point. Active matrix LCDs (AMLCDs) use metal-insulator-metal (MIM) diodes or thin film transistors (TFT) at each pixel to control the pixel's on / off state. Display technologies include Color Super-Twist Nematic (CSTN), Double Layer Super-Twist Nematic (DSTN), High-Performance Addressing (HPA), and Thin Film Transistor (TFT).
Video standards that apply to all types of flat panel displays include VGA, XGA, SVGA, SXGA, and UXGA. Video Graphics Array (VGA) is a PC video display circuit and adapter that supports text and graphics. Extended Graphics Array (XGA) is a high-resolution graphics standard introduced by IBM in 1990. Super Video Graphics Array (SVGA) is a set of graphics standards designed to offer greater resolution than VGA. Super Extended Graphics Array (SXGA) is a set of graphic standards designed to provide higher resolution than XGA. Ultra Extended Graphics Array (UXGA) is a set of graphic standards designed to provide higher resolution than either XGA or SXGA.
Important display specifications to consider when searching for flat panel displays include effective screen width and height, screen diagonal, luminance, horizontal and vertical viewing angles, the number of pixels both vertically and horizontally, the pixel pitch, the number of colors, the aspect ratio, and the image resolution in pixels. Screen size is usually given in a diagonal, but the width and length of the screen, not the whole display, may be given as well and referred to as effective screen width and effective screen height. Luminance is the luminous intensity per unit area projected in a given direction. May also be incorrectly termed brightness. Aspect ratios are typically 4:3 or 16:9. Image resolutions can be 640 x 480, 800 x 600, 1024 x 768, 1152 x 864, 1280 x 1024, and 1600 x 1200.
Other important specifications that should be taken into consideration when searching for flat panel displays include external connections, mounting options, features, and environmental operating conditions.