Computer Monitors

      The computer monitor is an output device that is part of your computer's display system. A cable connects the monitor to a video adapter (video card) that is installed in an expansion slot on your computer’s motherboard. This system converts signals into text and pictures and displays them on a TV-like screen (the monitor).

The computer sends a signal to the video adapter, telling it what character, image or graphic to display. The video adapter converts that signal to a set of instructions that tell the display device (monitor) how to draw the image on the screen.

Cathode Ray Tube (CRT)
The CRT, or Cathode Ray Tube, is the "picture tube" of your monitor. Although it is a large vacuum tube, it's shaped more like a bottle. The tube tapers near the back where there's a negatively charged cathode, or "electron gun". The electron gun shoots electrons at the back of the positvely charged screen, which is coated with a phosphorous chemical. This excites the phosphors causing them to glow as individual dots called pixels (picture elements). The image you see on the monitor's screen is made up of thousands of tiny dots (pixels). If you've ever seen a child's LiteBrite toy, then you have a good idea of the concept. The distance between the pixels has a lot to do with the quality of the image. If the distance between pixels on a monitor screen is too great, the picture will appear "fuzzy", or grainy. The closer together the pixels are, the sharper the image on screen. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. (see sidebar). You should try to get a monitor with a dot pitch of .28 mm or less.

Note: From an environmental point of view, the monitor is the most difficult computer peripheral to dispose of because of the lead it contains.

There are a couple of electromagnets (yokes) around the collar of the tube that actually bend the beam of electrons. The beam scans (is bent) across the monitor from left to right and top to bottom to create, or draw the image, line by line. The number of times in one second that the electron gun redraws the entire image is called the refresh rate and is measured in Hertz (Hz).
If the scanning beam hits each and every line of pixels, in succession, on each pass, then the monitor is known as a non-interlaced monitor. A non-interlaced monitor is preferred over an interlaced monitor. The electron beam on an interlaced monitor scans the odd numbered lines on one pass, then scans the even lines on the second pass. This results in an almost imperceivable flicker that can cause eye-strain.

This type of eye-strain can result in blurred vision, sore eyes, headaches and even nausea. Don't buy an interlaced monitor, they can be a real pain in the ... ask your optometrist.

Interlaced computer monitors are getting harder to find (good!), but they are still out there, so keep that in mind when purchasing a monitor and watch out for that "steal of a deal".

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