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CompTIA A+ Certification All-in-One Exam Guide

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LCD Monitors

Almost every computing device today uses a liquid crystal display (LCD)

panel as the primary visual output component. LCDs vary a lot, as you might

imagine, considering the amazing variety of computing devices out there.

This section explores how LCDs work in the Historical/Conceptual area, and

then examines features that differentiate them.

Historical/Conceptual

How LCDs Work

The secret to understanding the most common type of LCD panels is to

understand the concept of the polarity of light. Anyone who played with a

prism in sixth grade or has looked at a rainbow knows that light travels in

waves (no quantum mechanics here, please!), and the wavelength of the light

determines the color. What you might not appreciate is the fact that light

waves emanate from a light source in three dimensions. It’s impossible to

draw a clear diagram of three-dimensional waves, so instead, let’s use an

analogy. To visualize this, think of light emanating from a flashlight. Now

think of the light emanating from that flashlight as though someone was

shaking a jump rope. This is not a rhythmic shaking, back and forth or up and

down; it’s more as if a person went crazy and was shaking the jump rope all

over the place—up, down, left, right—constantly changing the speed.

That’s how light really acts. Well, I guess we could take the analogy one

step further by saying the person has an infinite number of arms, each

holding a jump rope shooting out in every direction to show the threedimensionality

of light waves, but (a) I can’t draw that and (b) one jump rope

will suffice to explain the typical LCD panels. The varying speeds create

wavelengths, from very short to very long. When light comes into your eyes

at many different wavelengths, you see white light. If the light came in only

one wavelength, you would see only that color. Light flowing through a

polarized filter (like sunglasses) is like putting a picket fence between you

and the people shaking the ropes. You see all of the wavelengths, but only the

waves of similar orientation. You would still see all of the colors, just fewer

of them because you only see the waves of the same orientation, making the

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