The display technology employed in plasma TVs and LCD TVs is called "flat panel display (FPD) technology," and its operating principle and structure are completely different from those of conventional CRT TVs.

The following briefly explains the image display mechanism and features of FPDs, such as plasma display panels (PDPs) and liquid crystal displays (LCDs), by comparing it with the image display mechanism of CRT TVs.

CRT stands for "Cathode Ray Tube." In this system, electron beams from electron guns in a flask-shaped, glass vacuum tube collide with phosphor on the screen, causing light to be emitted. The deflection coil controls the paths of the electron beams, forcing them to scan (draw lines) horizontally from top to bottom across the screen at high speed in order to display the image (Fig. 2).

In contrast, the flat panels used in PDPs and LCDs have numerous imaging pixels. Instead of the scanning method used by CRT TVs for the display of images, individual imaging pixels serve as "dots," and together form a dot matrix system. Although PDPs and LCDs are both FPDs, the mechanisms of their imaging pixels are quite different.

In a PDP, the layer of phosphors sealed between two glass plates, which constitutes a discharge space, is filled with a gas, as shown in Fig. 3. A voltage is applied to the gas, inducing plasma discharges that, in turn, produce ultraviolet rays. When these ultraviolet rays strike the phosphors of the three primary colors (RGB: red, green and blue), the phosphors emit lights of corresponding colors. In other words, there are numerous tiny "fluorescent lamps" of three colors (RGB) arranged on a screen, and they turn ON and OFF at high speed to display the image.

In an LCD, on the other hand, a liquid crystal layer (a material consisting of liquid crystal molecules in an intermediate state between solid and liquid) is sandwiched between two glass plates, as shown in Fig. 4. A light source (backlight) installed behind the rear glass plate provides light. The polarizing characteristic (allowing only light oscillating in a certain direction to pass) of the liquid crystals changes when a voltage is applied. By utilizing this unique characteristic of the liquid crystals to block light and allow light to pass through, the LCD screen displays images.

Put simply, PDPs are light-emitting displays, while LCDs are light-receiving (non-light emitting) displays.