In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, and William Crookes showed they could be deflected by magnetic fields. Hittorf observed that some unknown rays were emitted from the cathode (negative electrode) which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. History Discoveries Braun's original cold-cathode CRT, 1897Ĭathode rays were discovered by Julius Plücker and Johann Wilhelm Hittorf. The electrons are steered by deflection coils or plates, and an anode accelerates them towards the phosphor-coated screen, which generates light when hit by the electrons. Ī CRT works by electrically heating a tungsten coil which in turn heats a cathode in the rear of the CRT, causing it to emit electrons which are modulated and focused by electrodes. Flat-panel displays can also be made in very large sizes whereas 40–45 inches (100–110 cm) was about the largest size of a CRT. Since the mid–late 2000's, CRTs have been superseded by flat-panel display technologies such as LCD, plasma display, and OLED displays which are cheaper to manufacture and run, as well as significantly lighter and thinner. This tube makes up most of the weight of CRT TVs and computer monitors. The face is typically made of thick lead glass or special barium- strontium glass to be shatter-resistant and to block most X-ray emissions. As such, handling a CRT carries the risk of violent implosion that can hurl glass at great velocity. Thus, the interior is evacuated to less than a millionth of atmospheric pressure. Its interior must be close to a vacuum to prevent the emitted electrons from colliding with air molecules and scattering before they hit the tube's face.

The tube is a glass envelope which is heavy, fragile, and long from front screen face to rear end. The rear of an LG.Philips Displays 14-inch color cathode-ray tube showing its deflection coils and electron guns Typical 1950s United States monochrome CRT TV Snapshot of a CRT TV showing the line of light being drawn from left to right in a raster pattern Animation of image construction using the interlacing method Color computer monitor electron gun Electrostatic deflection is commonly used in oscilloscopes. In modern CRT monitors and TVs the beams are bent by magnetic deflection, using a deflection yoke. In color devices, an image is produced by controlling the intensity of each of three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference. In CRT TVs and computer monitors, the entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called a raster. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. A CRT in a TV is commonly called a picture tube.

The images may represent electrical waveforms on an oscilloscope, a frame of video on an analog television set (TV), digital raster graphics on a computer monitor, or other phenomena like radar targets. The only visible differences are the single electron gun, the uniform white phosphor coating, and the lack of a shadow mask.Ī cathode-ray tube ( CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen.

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