How Does a Cathode Ray Tube Work?


Anyone who owned a computer in the 20th century probably remembers the cathode ray tube monitor, the bulky video display units that came standard with PCs of the time. Essentially, CRTs were televisions with specialized inputs to display digital content. They were the mainstay of computer display technology for decades, until lighter and more efficient LCD monitors began to edge them out of the market.

Cathode Ray Tubes

  • A cathode ray tube monitor has three main components. At the rear of the monitor is a cathode ray gun that fires electrons out in a straight line. Next, a series of magnetic anodes can bend the path of those electrons, directing them toward a specific area. Finally, a screen composed of red, green and blue phosphor dots lies beneath the front glass of the monitor. When the beam of electrons hits these phosphor dots, they glow, and depending on which dots illuminate, the CRT can display various colors in the target area. The electron beam sweeps over the screen many times per second, allowing the monitor to display rapid movement.

Disadvantages of CRTs

  • The biggest disadvantage of cathode ray tube monitors was the size and weight of the hardware. The main body of the monitor consisted of a vacuum-sealed compartment for the components, and the larger the monitor, the further away the gun needed to be from the screen. This meant that larger monitors required proportionately more space behind the screen, and large monitors could become extremely heavy and difficult to move. In addition, CRTs could suffer from "burn-in," where leaving a static image on the screen for too long could damage the phosphor dots, resulting in a ghostly image left on the screen even when turned off.

Liquid Crystal Displays

  • Over time, liquid crystal display technology began to supplant cathode ray tubes. An LCD monitor consists of a flat panel with a static backlight, often a fluorescent panel. A sheet of liquid crystal lies between this light source and colored pixels at the front of the screen, and an electrical charge can make this liquid crystal transparent, opaque or any shade in between. By manipulating the liquid crystal matrix, the monitor can change the color and brightness of the image displayed on the screen.

Advantages of LCDs

  • LCD monitors quickly became popular due to their relatively small size in comparison to CRTs. Where a CRT monitor often had to be almost as deep as it was wide, LCDs could produce a superior picture while only being a few inches thick. This greatly reduced the weight of the units, and made these monitors much easier to install in non-standard setups such as wall mounts.

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