Video Hardware - Upgrading and Repairing PCs - page 819

or less in standby mode. LCD monitors comply with the far more stringent Energy 2000
(E2000) standard developed in Switzerland. E2000 requires that monitors use less than 5
watts when in standby mode. Note that LCD displays generally use one-third less power
than CRTs in either operating or standby mode.
LCD Technology
Because of their light weight, smaller overall size, and much greater clarity, LCD panels
havereplacedCRTdisplaysinvirtuallyallnewcomputerinstallations.DesktopLCDpan-
els use the same technology that first appeared in laptop computers. Compared to CRTs,
LCDs have completely flat, thin screens and low power requirements (30 watts versus up
to 100 watts or more for CRT monitors). The color quality of a good active-matrix LCD
panel can exceed that of many CRT displays, particularly when viewed from head on.
How LCD Displays Work
In an LCD, polarizing filters allow only light waves that are aligned with the filter to pass
through. After passing through one polarizing filter, all the light waves are aligned in the
same direction.
A second polarizing filter aligned at a right angle to the first blocks all those waves. By
changing the angle of the second polarizing filter, you can change the amount of light al-
lowedtopassaccordingly.Itistheroleoftheliquidcrystalcelltoactasapolarizingfilter
that can change the angle of polarization and control the amount of light that passes. The
liquid crystals are tiny rod-shaped molecules that flow like a liquid. They enable light to
pass straight through, but an electrical charge alters their orientation, which subsequently
alters the orientation of light passing through them. In a color LCD, there are three cells
for each pixel—one each for displaying red, green, and blue—with a corresponding tran-
sistor for each cell. The red, green, and blue cells that make up a pixel are sometimes re-
ferred to as subpixels . See Figure 12.21 .
Figure 12.21 A diagram illustrating a typical color LCD display.