How does a computer screen work?

How does a computer screen work?

Everyone knows what a computer monitor is. Computers are such an integral part of our life that almost everyone has had some contact with a computer monitor. But how do they work?

The first concept we need to understand is that of the pixel. If you take a magnifying glass and look at the screen of your computer monitor or television set while it’s turned on, you’ll notice that the picture is actually made up of thousands of dots of light.

Each of these dots is a pixel. Pixel incidentally is a shorthand term for “picture element”. Most of us have heard of pixels if only because digital cameras are rated in megapixels. The prefix mega means one million. So now you know that if you have a 2.1-megapixel camera, every picture will have 2.1 million dots in it. Go ahead, count ‘em if you don’t believe me.

We also know that the higher the number of megapixels the better the camera is considered to be. Why? Suppose you had a picture that was one inch by one inch and it had 50 pixels per inch. This is about what you see if your computer monitor is set to a resolution of 640 X 480 pixels. Each pixel is about 1/64 of an inch from its neighbor and to the eye the individual pixels blend together and form a continuous picture.

Now enlarge this picture to 10 X 10 inches. The pixels are now ten times as large and the space between them is over 1/8th inch. Now your eye can easily see each pixel and the picture looks terrible. The greater the number of pixels, the larger you can make the image, and the closer you can look without seeing the individual pixels. This is what is meant by higher resolution.

So the screen of your computer monitor is made up of dots (pixels) and the more dots there are per inch of the screen the higher the resolution and the better the screen images look. Now we have to discuss how the monitor makes those dots light up. There are several different technologies used for monitors but by far the most common is the same as that used for years in television sets.

Early experimenters with electricity found that they were able to produce a stream of sub-microscopic negatively charged particles (electrons) by electrically heating a metal filament in a vacuum. Because these particles were negatively charged, their direction could be changed by sending them between two metal plates one of which was charged positive and one negative. By adjusting the amount of charge on the plates the amount of change in direction could be varied. This device became known as an electron beam gun.

At about the same time, certain compounds were discovered that glowed whenever they were struck by electrons. These were called phosphors. Combining these two elements produced what is known as a cathode ray tube. The picture tube in your TV set is a cathode ray tube. The tube is a vaguely pyramid-shaped affair. The base of the pyramid is the screen. The inside of the screen is coated with phosphors and the electron gun is located at the point of the pyramid.

A very thin beam of electrons is sent towards the screen and electrical circuits between the gun and screen bend the beam so that it swings from side to side and up and down. Each side to side swing creates a line across the screen and when the beam reaches the edge of the screen, it moves down and creates another line just below the first. When the bottom of the screen is reached the beam returns to the top and starts over.

So now we can create a series of lines on the screen but how do we make a picture? If you turn the beam on full strength, the line will be bright white, if you turn the beam off, the line will be black. Anything in between will produce various shades of gray. So we produce a picture by varying the intensity of the beam while it is swinging back and forth. Of course all of this happens so quickly that your eye doesn’t see any of it. Only the overall picture is visible. But, you ask, what about color?

The secret to producing a color picture lies in the fact that any color can be produced by combining varying amounts of red, green and blue. Researchers soon found phosphors that glowed red or green or blue when struck by electrons of certain strengths. They also found ways to create three streams of electrons from one gun.

The last leap was to be able to coat the inside of the screen with phosphors in such a way that each pixel actually contained a dot of a red phosphor, a dot of green phosphor, and a dot of yellow phosphor. So now you had three guns sweeping across the screen each one varying in intensity to create just the right color on each pixel. Now, do you understand why it took so long to produce a reliable color TV set? And aren’t you amazed that they are as cheap and reliable as they are?

This is the technology that is inside most computer monitors. They look like small TV sets because basically that’s what they are. The other type of monitor that is beginning to become common is the flat panel monitor. The most often used technology in these devices is the liquid crystal display. Remember mood rings from the ‘70s? Mood rings were the public’s first introduction to liquid crystals.

These were liquids that changed colors as their temperature varied. You can still buy desk thermometers made with this technology. Other liquid crystals were found to change color when subjected to electricity. These are the kind used for flat panel monitors. Two sheets of glass have rows of very fine almost invisible wire placed on them. One row runs side to side, the other top to bottom. These sheets are put together with a layer of liquid crystal between them.

When electricity is applied to one of the up and down wires and also to one of the side to side wires, the point where they intersect glows with a color that depends on the intensity of the electricity. This creates one pixel of the image. Creating the entire image requires many scans at speeds much faster than your eye can see.

There are some other technologies being developed for use in monitors but these are the two major types in use now. Understanding a little about how these devices work gives you a real appreciation of the science and technology that created them.

Leave a Comment