en.wikipedia.org/wiki/Cathode_ray_tube#Ionizing_radiation
fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen.
electrostatic deflection is used, rather than the magnetic deflection commonly used with television and other large CRTs. The beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below.
edit Phosphor persistence Various phosphors are available depending upon the needs of the measurement or display application. The brightness, color, and persistence of the illumination depends upon the type of phosphor used on the CRT screen.
graticule as part of the visual display, to facilitate measurements. The graticule may be permanently marked inside the face of the CRT, or it may be a transparent external plate.
edit Color CRTs Spectra of constituent blue, green and red phosphors in a common CRT Color tubes use three different phosphors which emit red, green, and blue light respectively.
Color CRTs have three electron guns, one for each primary color, arranged either in a straight line or in a triangular configuration (the guns are usually constructed as a single unit).
Magic eye tube In better quality tube radio sets a tuning guide consisting of a phosphor tube was used to aid the tuning adjustment. Tuning would be adjusted until the width of a radial shadow was minimized.
stencil), which shapes a wide electron beam to form a character on the screen. The system selects a character on the mask using one set of deflection circuits, but that causes the extruded beam to be aimed off-axis, so a second set of deflection plates has to re-aim the beam so it is headed toward the center of the screen. A third set of plates places the character wherever required. The beam is unblanked (turned on) briefly to draw the character at that position. Graphics could be drawn by selecting the position on the mask corresponding to the code for a space (in practice, they were simply not drawn), which had a small round hole in the center; this effectively disabled the character mask, and the system reverted to regular vector behavior.
These had 10 electron guns which produced electron beams in the form of digits in a manner similar to that of the charactron. The tubes were either simple single-digit displays or more complex 4- or 6- digit displays produced by means of a suitable magnetic deflection system.
edit Demise Although a mainstay of display technology for decades, CRT-based computer monitors and televisions constitute a dead technology. The demand for CRT screens has dropped precipitously since 2000, and this falloff has been accelerating in the latter half of that decade.
In Canada and the United States, the sale and production of high-end CRT TVs (30-inch screens) in these markets has all but ended by 2007; just a couple years later inexpensive combo CRT TVs (20-inch screens with an integrated VHS or DVD player) have disappeared from discount stores. It has been common to replace CRT-based televisions and monitors in as little as 5-6 years, although they generally are capable of satisfactory performance for a much longer time. Electronics retailers such as Best Buy have been steadily reducing store spaces for CRTs. In 2005, Sony announced that they would stop the production of CRT computer displays.
The demise of CRT, however, has been happening more slowly in the developing world. According to iSupply, production in units of CRTs was not surpassed by LCDs production until 4Q 2007, owing largely to CRT production at factories in China.
DSG (Dixons), the largest retailer of domestic electronic equipment, reported that CRT models made up 80-90% of the volume of televisions sold at Christmas 2004 and 15-20% a year later, and that they were expected to be less than 5% at the end of 2006.
edit Causes CRTs, despite recent advances, have remained relatively heavy and bulky and take up a lot of space in comparison to other display technologies. CRT screens have much deeper cabinets compared to flat panels and rear-projection displays for a given screen size, and so it becomes impractical to have CRTs larger than 40 inches (102 cm).
LCD and plasma flat-panels which allow them to easily surpass 40 inches (102 cm) as well as being thin and wall-mountable, two key features that were increasingly being demanded by consumers. By 2006, although the price points of CRTs are generally much lower than LCD and plasma flat panels, large screen CRTs (30-inches or more) are as expensive as a similar-sized LCD.
X-ray radiation as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered unharmful.
By the time personal computers were produced, glass in the front panel (the viewable portion of the CRT) used barium rather than lead, though the rear of the CRT was still produced from leaded glass. Monochrome CRTs typically do not contain enough leaded glass to fail EPA tests.
vacuum exists within all cathode ray tubes, putting the envelope under relatively high stress. If the outer glass envelope is damaged, the glass will break and pieces will fly out at high speed.
but considers CRTs that have been set aside for testing to be commodities if they are not discarded, speculatively accumulated, or left unprotected from weather and other damage.
Maximum practical size is around 24 inches for computer monitors; most direct view CRT televisions are 36 inches or smaller, with regular-production models limited to about 40 inches.
"Occupational Risks Associated with Electronics Demanufacturing and CRT Glass Processing Operations and the Impact of Mitigation Activities on Employee Safety and Health" (PDF).
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