Plasma Display
    For the past 75 years, the vast majority of televisions have been built around the same technology: the cathode ray tube (CRT). Cathode ray tubes produce crisp, vibrant images, but they do have a serious drawback: They are bulky. In order to increase the screen width in a CRT set, you have to increase the length of the tube. Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable chunk of a room. Recently, a new alternative has popped up on store shelves: the plasma flat panel display. These televisions have wide screens, comparable to the largest CRT sets, but they are only about 6 inches (15 cm) thick.
Display Basics
    The basic idea of a plasma display is to illuminate tiny colored fluorescent lights to form an image. Each pixel is made up of three fluorescent lights -- a red light, a green light and a blue light. Just like a CRT television, the plasma display varies the intensities of the different lights to produce a full range of colors.
Tuning In
    Most plasma displays aren't technically televisions, because they don't have a television tuner. The television tuner is the device that takes a television signal (the one coming from a cable wire, for example) and interprets it to create a video image.
    Like LCD monitors, plasma displays are just monitors that display a standard video signal. To watch television on a plasma display, you have to hook it up to a separate unit that has its own television tuner, such as a VCR.
What is Plasma?
    The central element in a fluorescent light is plasma, a gas made up of free-flowing ions (electrically charged atoms) and electrons (negatively charged particles). Under normal conditions, a gas is mainly made up of uncharged particles. That is, the individual gas atoms include equal numbers of protons (positively charged particles in the atom's nucleus) and electrons. The negatively charged electrons perfectly balance the positively charged protons, so the atom has a net charge of zero.
    If you introduce many free electrons into the gas by establishing an electrical voltage across it, the situation changes very quickly. The free electrons collide with the atoms, knocking loose other electrons. With a missing electron, an atom loses its balance. It has a net positive charge, making it an ion.
    In a plasma with an electrical current running through it, negatively charged particles are rushing toward the positively charged area of the plasma, and positively charged particles are rushing toward the negatively charged area.
    In this mad rush, particles are constantly bumping into each other. These collisions excite the gas atoms in the plasma, causing them to release photons of energy. Xenon and neon atoms, the atoms used in plasma screens, release light photons when they are excited. Mostly, these atoms release ultraviolet light photons, which are invisible to the human eye. But ultraviolet photons can be used to excite visible light photons, as we'll see in the next section.
Inside the Display: Gas and Electrodes
    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, on both sides of 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 above the cell, along the front glass plate.
    Both sets of electrodes extend across the entire screen. The display electrodes are arranged in horizontal rows along the screen and the address electrodes are arranged in vertical columns. As you can see in the diagram below, the vertical and horizontal electrodes form a basic grid.
    To ionize the gas in a particular cell, the plasma display's computer charges the electrodes that intersect at that cell. It does this thousands of times in a small fraction of a second, charging each cell in turn.
    When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. As we saw in the last section, the current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.
Inside the Display: Phosphors
    The released ultraviolet photons interact with phosphor material coated on the inside wall of the cell. Phosphors are substances that give off light when they are exposed to other light. When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons jumps to a higher energy level and the atom heats up. When the electron falls back to its normal level, it releases energy in the form of a visible light photon.
    The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate sub-pixel cells, each with different colored phosphors. One sub-pixel has a red light phosphor, one sub-pixel has a green light phosphor and one sub-pixel has a blue light phosphor. These colors blend together to create the overall color of the pixel.
    By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each sub-pixel color to create hundreds of different combinations of red, green and blue. In this way, the control system can produce colors across the entire spectrum.
Pros and Cons
    The main advantage of plasma display technology is that you can produce a very wide screen using extremely thin materials. And because each pixel is lit individually, the image is very bright and looks good from almost every angle. The image quality isn't quite up to the standards of the best cathode ray tube sets, but it certainly meets most people's expectations.
    The biggest drawback of this technology has to be the price. With relatively high prices, these sets aren't exactly flying off the shelves. But as prices fall and technology advances, they may start to edge out the old CRT sets. In the near future, setting up a new TV might be as easy as hanging a picture!