Cutaway rendering of a color CRT:
Three electron emitters (for red, green, and blue phosphor dots)
Connection for second anode (referred to as the "ultor" in some receiving tube manuals)
Mask for separating beams for red, green, and blue part of displayed image
Phosphor layer (screen)with red, green, and blue zones
Close-up of the phosphor-coated inner side of the screen
The cathode ray tube (CRT) is a
vacuum tube that contains one or more
electron guns and a
phosphorescent screen, and is used to display images.
 It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. The images may represent electrical
oscilloscope), pictures (television,
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).
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
electronic test instrument.
A 14-inch cathode ray tube showing its deflection coils and electron guns
Typical 1950s United States
A CRT is constructed from a glass envelope which is large, deep (i.e., long from front screen face to rear end), fairly heavy, and relatively fragile. The interior of a CRT is
evacuated to approximately 0.01 Pa
 to 133 nPa.,
 evacuation being necessary to facilitate the free flight of electrons from the gun(s) to the tube's face. That it is evacuated makes handling an intact CRT potentially dangerous due to the risk of breaking the tube and causing a violent
implosion that can hurl shards of glass at great velocity. 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Since the late 2000s, CRTs have been largely superseded by newer "
flat panel" display technologies such as
plasma display, and
OLED displays, which in the case of LCD and OLED displays have lower manufacturing costs and power consumption, as well as significantly less weight and bulk. Flat panel displays can also be made in very large sizes; whereas 38" to 40" was about the largest size of a CRT television, flat panels are available in 60" and larger sizes.