Hardware Reference
In-Depth Information
about half the energy of standard LCD panels.
Figure 12.24 illustrates how an LED backlit screen works.
Figure 12.24. How an LED backlit display works.
CRT Display Technology
CRT technology is the same used in older television sets. In the past few years, CRTs have vanished
from store shelves, mainly due to the availability of lower-cost LCDs. However, many older systems
still use CRT monitors. CRTs consist of a vacuum tube enclosed in glass. One end of the tube
contains an electron gun assembly that projects three electron beams, one each for the red, green, and
blue phosphors used to create the colors you see onscreen; the other end contains a screen with a
phosphorous coating.
When heated, the electron gun emits a stream of high-speed electrons that are attracted to the other
end of the tube. Along the way, a focus control and deflection coil steer the beam to a specific point
on the phosphorous screen. When struck by the beam, the phosphor glows. This light is what you see
when you watch TV or look at your computer screen. Three layers of phosphors are used: red, green,
and blue. A metal plate called a shadow mask aligns the electron beams; it has slots or holes that
divide the red, green, and blue phosphors into groups of three (one of each color).
Monitors based on Sony Trinitron or Mitsubishi DiamondTron picture tubes used an aperture grille
type mask to separate red, green, and blue phosphors, resulting in strips of square pixels in a linear
arrangement, similar to an LCD. NEC's ChromaClear monitors used a variation on the aperture grille
called the slotted mask , which is brighter than standard shadow-mask monitors and more
mechanically stable than aperture grille-based monitors. This resulted in a staggered pixel
arrangement.
Various types of shadow masks affect picture quality, and the distance between each group of three
(the dot or pixel pitch ) affects picture sharpness.
See “ Pixels , p. 653 .
Figure 12.25 illustrates the interior of a typical CRT.
 
 
 
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