What is "cathode ray tube"

n. (context electronics English) A vacuum tube that displays still or moving images (such as for a television), by controlling the direction of a cathode ray emitted towards the front of the tube. The front is coated by a layer of fluorescent material, so that it emits light when struck by the beam.

The cathode ray tube (CRT) is a vacuum tube containing one or more electron guns, and a phosphorescent screen used to view images. It has a means to accelerate and deflect the electron beam(s) onto the screen to create the images. The images may represent electrical waveforms ( oscilloscope), pictures ( television, computer monitor), radar targets or others. CRTs have also been used as memory devices, in which case the visible light emitted from the fluorescent material (if any) is not intended to have significant meaning to a visual observer (though the visible pattern on the tube face may cryptically represent the stored data).

The CRT uses an evacuated glass envelope which is large, deep (i.e. long from front screen face to rear end), fairly heavy, and relatively fragile. As a matter of safety, the face is typically made of thick lead glass so as to be highly shatter-resistant and to block most X-ray emissions, particularly if the CRT is used in a consumer product. Since the early 2000s (decade), CRTs have largely been superseded by newer display technologies such as LCD, plasma display, and OLED screens, which have lower manufacturing costs and power consumption, and significantly less weight and bulk. Newer display technologies can also be made in larger sizes; whereas 38" to 40" was about the largest size of a CRT TV, new display technologies are available in 50" to 60" and even larger sizes. The vacuum level inside the tube is high vacuum on the order of to

In television sets and computer monitors, the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. An image is produced by controlling the intensity of each of the three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference. In all modern CRT monitors and televisions, the beams are bent by magnetic deflection, a varying magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although electrostatic deflection is commonly used in oscilloscopes, a type of diagnostic instrument.