Plasma Television

Television has been around since 19th century and for the past 50 years it held a pretty common place in our leaving room. Since the invention of television engineers have been striving to produce slim & flat displays that would deliver as good or even better images than the bulky C.R.T. Scores of research teams all over the world have been working to achieve this. Plasma television has achieved this goal. Technologies inside it are plasma and hi-definition which are just two of the latest technologies to hit stores. The main contenders in the flat race are PDP (Plasma Display Panel) and flat CRT with LCD and FED (Field Emission Display) To get an idea of what makes a plasma display different it needs to understand how a conventional TV set works. Conventional TV’s used CRT to create the images we see on the screen. The cathode is a heated filament, like the one in a light bulb. It is housed inside a vacuum created in a tube of thick glass….that is what makes your TV so big and heavy. The newest entrant in the field of flat panel display systems is Plasma display. Plasma display panels don’t contain cathode ray tubes and pixels are activated differently.

Plasma displays are bright (1000 lux or higher for the module), have a wide color gamut, and can be produced in fairly large sizes, up to 381 cm (150 inches) diagonally. They have a very low-luminance "dark-room" black level compared to the lighter grey of the unilluminated parts of an LCD screen. The display panel is only about 6 cm (2.5 inches) thick, while the total thickness, including electronics, is less than 10 cm (4 inches). Plasma displays use as much power per square meter as a CRT or an AMLCD television. Power consumption varies greatly with picture content, with bright scenes drawing significantly more power than darker ones. Nominal power rating is typically 400 watts for a 50-inch (127 cm) screen. Post-2006 models consume 220 to 310 watts for a 50-inch (127 cm) display when set to cinema mode. Most screens are set to 'shop' mode by default, which draws at least twice the power (around 500-700 watts) of a 'home' setting of less extreme brightness.

The lifetime of the latest generation of plasma displays is estimated at 60,000 hours of actual display time, or 27 years at 6 hours per day. This is the estimated time over which maximum picture brightness degrades to half the original value, not catastrophic failure.

Competing displays include the CRT, OLED, AMLCD, DLP, SED-tv, and field emission flat panel displays. Advantages of plasma display technology are that a large, very thin screen can be produced, and that the image is very bright and has a wide viewing angle.

The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, in front of and behind the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted in front of the cell, along the front glass plate. Control circuitry charges the electrodes that cross paths at a cell, creating a voltage difference between front and back and causing the gas to ionize and form a plasma. As the gas ions rush to the electrodes and collide, photons are emitted.

In a monochrome plasma panel, the ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes – even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.

In color panels, the back of each cell is coated with a phosphor. The ultraviolet photons emitted by the plasma excite these phosphors to give off colored light. The operation of each cell is thus comparable to that of a fluorescent lamp.

Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel, analogous to the "triad" of a shadow-mask CRT. By varying the pulses of current flowing through the different cells thousands of times per second, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce most of the visible colors. Plasma displays use the same phosphors as CRTs, which accounts for the extremely accurate color reproduction.