Types of displays

CRT Display. Video display can be accomplished by a cathode ray tube (CRT), commonly used in television sets. Display on a CRT screen is accomplished by an electron beam that scans across and down the screen, and then returns to the upper left-hand corner to repeat the process. The technique leaves points of light on the inside phosphor-coated surface of the tube. The beam current is either increased to make a lighter point (pixel) or decreased to make a darker point (pixel) along each of the scan lines.

The display creates a complete image 80 times per second (80 Hz). A drawback to this refresh rate is that in many applications, the screen flickers causing eyestrain and fatigue. This problem can be eliminated by in­creasing the refresh rate (usually to 70 or 80 Hz) to create flicker-free images. Gen­erally, the higher the refresh rate, the higher the cost of the display.

CRTs use three separate elec­tron beams that represent the primary additive colours, red, blue, and green. The beams are focused so that their dot pat­terns slightly overlap on the screen to create the desired colours.

Nowadays CRTs are being ousted by liquid crystal displays (LCDs).

Liquid Crystal Displays (LCDs). The most common type of flat panel is the liquid crystal display (LCD)—a liquid-filled display surface that, when electrically charged, creates images us­ing ambient light. The historical drawback to LCDs has been their lack of clarity. Because early LCDs produced no light of their own but instead relied on reflected light for viewing, they had a very narrow range of viewing angles and could only be seen clearly if you looked at them straight on. To compensate for this deficiency, manufacturers are dealing with the problem in several ways. The first is to backlight the LCD by adding lights that shine through the LCD screen from be­hind, thus providing a clearer image. The second is to build LCDs with supertwist crystals, which refract or twist the light to provide much higher con­trast (e.g., darker characters against a lighter background). Higher contrast also makes a wider viewing angle pos­sible when looking at the display. The third is to place a transistor at each pixel location on the display. This technique, known as active-matrix technology, produces a high-contrast display at the cost of consuming more power.

Active-matrix technology. Active-matrix LCDs depend on thin film transistors (TFT). Basically, TFTs are tiny switching transistors and capacitors. They are arranged in a matrix on a glass substrate. To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle. And if we carefully control the amount of voltage supplied to a crystal, we can make it untwist only enough to allow some light through. By doing this in very exact, very small increments, LCDs can create a gray scale. Most displays today offer 256 levels of brightness per pixel.

Plasma displays Plasma display technology is a new emissive" flat panel technology which gives the rich accurate colour fidelity of conventional Cathode Ray Tube (CRT) monitors in a large plasma display that is thin enough to hang on the wall. It's the best way to achieve flat panel display with excellent image quality and large screen sizes viewable in any environment. This plasma display technology known as “ plasma vision " is an array of cells, known as pixels, which are composed of 3 sub-pixels, corresponding to the colours red, green and blue. Gas in plasma state is to react with phosphors in each sub-pixel to produce coloured light (red, green or blue). These phosphors are the same types used in conventional cathode ray tube (CRT) devices such as televisions and standard computer monitor displays. You get the rich, dynamic colours you expect from plasma display. Each subpixel is individually controlled by advanced electronics to produce over 16 million different colours.

TFT panels Using the latest technology such as PVA (patterned vertical alignment) TFT panels offer fast response time, 170-degree viewing angles, high brightness and enhanced contrast to give the optimum solution.

Coupled with DT's interface solutions (RGB, video, and DVI), single board computer (SBC), and touchscreen options customers can source exactly the solutions they need.

There is a huge replacement market for plasma screens that have suffered from image burn-in, unreliable fans and heat dissipation issues, whereas TFTs offer higher resolution, lower power, reduced weight, no burn-in, as well as excellent viewing angles, higher brightness and contrast.

Although still more expensive than plasma, many companies have now calculated that the TFT LCD still offers a lower-cost long-term option than plasma. TFTs have a 5 year plus lifetime expectancy plus replaceable backlights possible whereas plasma needs often to be replaced after only around 2 years. The lifetime costs are in fact lower for TFT than plasma, plus they offer many advantages. TFTs are ready to oust plasma eventually to a relatively niche application product.