How It Works: CRT

Standard glass-tube televisions and your CRT monitor work quite similarly. A glass cathode-ray tube (1), which contains a vacuum, has three electron guns (2) at its narrow end, each containing an anode and cathode assembly. As you may recall from high-school science, the cathodes emit electrons; the anodes draw the electrons away from the cathodes, focusing and accelerating them into electron beams (3). The deflection yoke (4), around the tube base, precisely manipulates the three beams via electromagnetic force, working with the CRT's circuitry to sweep them across the screen in precise, horizontal lines. Where a beam hits the screen, it causes a red, green, or blue (RGB) phosphor dot (5) to glow; the screen's inner surface is coated with these colored phosphors. (The beams, though colorized in the illustration, are actually invisible.)
CRTs come in two main varieties: shadow mask and aperture grill. In shadow-mask models, the RGB phosphors on the inside of the screen are arranged as a staggered pattern of dots (see the inset); in the latter, they're not dots but repeating vertical RGB stripes. In a shadow-mask CRT, when the monitor receives commands from your PC's graphics adapter, the electron guns fire their three beams, in concert, through tiny holes in the shadow mask (6), a metal screen just behind the phosphor-coated display glass. (Aperture-grill monitors, popularly known as Trinitrons or Diamondtrons, work similarly, but vertical wires, not a mask, funnel the beams.) Their channeled beams illuminate a trio of phosphor dots (a triad (7)) lining the inside of the glass. A pixel (8)—the smallest image element you can see—comprises one or more triads; how many depends on the resolution you specify. The lower the resolution, the more triads that are assigned to each pixel.
The electron guns blaze across the screen, row by row, illuminating phosphors in their wake. Varying the beams' intensity strengthens or weakens the glow from a given phosphor dot; by careful manipulation of every one, the triads and pixels, seen by the eye as single units, create the illusion of different-color dots.
Phosphors don't glow for long, though. Once the guns have scanned the whole screen, they repeat the process—typically, 60 to 80 times a second. (This number is what is known as the refresh rate.) To comprehend the staggering scale of the task: A CRT running at 1,280x1,024 at a 75Hz refresh rate illuminates and re-illuminates nearly 100 million pixels per second.

How to Work CRT Watch This Video