Cathode Ray Tube (CRT) monitors are made up of three basic
parts:
Electron guns - In color CRTs, there are three guns. One for red, one
for green, and one for blue. They fire electrons down a vacuum tube to light up phosphors
on the screen (we'll get to that in a minute). Even though the name suggests that the
electron guns are color (red gun, green gun, blue gun), they do not actually fire colored
electrons. What each gun does, is to fire electrons only at its respectively colored
phosphors on the screen.
Steering magnet (focusing coil) - Once an electron has been fired from
the guns, there needs to be a way to steer or focus it onto the phosphor it needs to light
up on the screen. This is done by energizing magnets along the tube to deflect the
electron away from the tube walls and at the target phosphor. This is pretty complicated
in that there are extremely high tolerances involved. After all, an electron is very small
and is moving extremely fast. Without steering, you would have only one bright dot right
in the middle of your screen. The speed at which the steering can manipulate the electrons
determines your refresh rate. The refresh rate is very important, as it directly affects
how fluid and flicker-free your screen will appear. More on refresh rates after I explain
phosphors.
Phosphor coated screen - This is the part of your monitor you see
every day, with exception to the fact that you are looking at it from the outside. On the
inside, the screen is coated with phosphors which glow for a short duration after being
struck with energy. The amount of time it glows after being struck is called persistence).
If you remember, I said there are three electron guns. Because electrons aren't colored,
the phosphors must be. That means for every pixel (picture element) on the screen, there
are three phosphors (red, green and blue), arranged in what is called a triad. The
closeness (density) of these triads determines your monitors dot pitch in millimeters (you
usually see these represented as .28, .26, .25 etc., and I'll get into this in a little
bit.)
