The CRT, or cathode ray tube, is the oldest technology currently available.
Yet its operation is relatively easy and straight forward.
The cathode ray tube is an evacuated glass bottle, with a heating element on one
end and a phosphor-coated screen on the other. The heating element, called a
filament, creates free electrons. These electrons are accelerated and funneled
away from the filament by the strong positive charge of the focusing anode
cylinders and accelerating anodes (sometimes called an electron gun), ultimately
creating an electron beam.
This beam can be directed vertically and horizontally to a pair of weekly charged
deflection plates (also called deflection yokes). The deflection plates have
opposite charges - one negative and one positive, to attract and repel the
electron beam.
The electrons are sent speeding out of the yolk of the tube toward the
phosphor-coated screen on the opposite end, which in turn causes the phosphor
to glow. See Figure 1.
Figure 1
Color televisions will have three electron guns, one each to excite the red,
green, and blue phosphors coating the opposite side of the cathode ray tube.
All of the colors that we see are made up of a combination of the three primary
colors: red, green and blue.
The inside of the CRT tube is covered by arrays of these three colored
phosphors as shown in Figure 2.
Figure 2
If an area of the screen needs to be white, the red, green and blue dots
grouped together in that area will be excited simultaneously.
If green is the only color needed, then only the green is excited, and so
forth. In this way, any area of the CRT can be a different color, with all
of the areas working together to paint an image on the screen.
We hope that this straight forward explanation is helpful to you. If you have
further questions, please email us at
info@theprojectorpros.com
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