An Overview of Display Device Types – CompTIA A+ 220-801: 1.10

| October 15, 2012

There are many ways to display the output from your computer. In this video, you’ll learn about CRTs, LCD technology, LED and OLED, plasma displays, and digital projector technology.

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Review Quiz: An Overview of Display Device Types

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The old style CRT is one that used a fluorescent tube and electrons to paint the screen one line at a time. These particular heavy monitors were configured for certain sizes. So you might get a 15-inch, or 19-inch, or 21-inch or different other types of options for these big cathode ray tubes. Obviously, the larger the screen, the larger the tube and the larger the weight for these devices. They usually came with a standard set of resolutions that it would support. It might be things like XGA, which is 1024 by 768; SXGA, which is 1280 by 1024; or UXGA, which is 1600 by 1200 as its resolution.

An important specification for these older-style CRTs was something called refresh rate. This referred to how fast the electron gun in this device can paint an entire screen. The refresh rates of these devices tended to be about 65 to 75, sometimes 85, hertz. That means that we could refresh the screen 85 times in a single second.

What we started to see as the resolutions got larger is the electron beam took longer to be able to update and refresh the entire screen. And as those refresh rates drop down to 65 hertz or lower, our human eye started to pick out flickering. We couldn’t exactly see the updating of the screen, but we can see the results of the screen being updated slower. And that caused fatigue, especially if you were sitting in front of your monitor for long periods of time.

These days a very common display type is LCD. That’s a liquid crystal display. We don’t have tubes. There’s no longer an electron gun. And we don’t have to worry so much about that electron gun painting the screen. Instead, we have a backlight that is always on on a liquid crystal display. And when we provide power to a transistor, it re-polarizes the light so that it can now come through and display a certain color.

This is why the LCD displays generally don’t have the blackest blacks, because you always have a light shining through. And you’ll find if you’re doing a lot of graphics work, or a lot of work that needs to be printed, you need very good color representation on the screen, you want to make sure that you have a very high-quality LCD because of that backlight.

There’s another type of display you’ll see called an LED display. And we call it an LED display because the backlight that normally is a fluorescent light is one that we are using instead an LED to provide that light. This is still an LCD providing the screen information, providing that view. So it’s probably more accurate to call this an LED-backlit LCD display.

This LED technology may be implemented a number of ways. One way is to have the LEDs around the edges of the screen. And there’s a diffuser inside of the display that then evenly distributes that light throughout the entire back.

Another way to implement this technology is with an entire array of LEDs. They’re not just around the edges. They’re throughout the entire back of the display. And that gives the display more control of lightening and darkening certain areas to make those blacks just a little bit blacker when you need them.

One of the newest kinds of LED displays is the organic LED display. This is using organic material that lights up when you provide it with a current. It’s got very low cost. You see it on a lot of mobile devices because it has a very fast response time and a very wide viewing angle. And you’re able to do a lot because the materials inside of it are organic.

Another type of modern display is the plasma display. A plasma display is one that has a tiny, tiny little cells all in the display itself. And those cells have inside of them a noble gas and mercury. When you provide a voltage to that, it creates a plasma that then sends out ultraviolet light. That ultraviolet light hits a phosphor that is on each one of those cells. And the phosphor glows a particular color. And now you can see the display that is being presented to you on the front screen.

Because we’re using these phosphors to provide the colors, we can have very, very deep blacks. If you’re working with something that will be going to a printer, if you’re doing video editing, this will provide very, very good color representation for you. These displays aren’t perfect, of course. They use a lot of power. And you’ll find because of the method they’re using to provide this color in the plasma, that they put off a lot of radio interference. If you live a long way above sea level, you’ll find that plasma displays become less effective as well. So make sure you check the specifications if you’re living in a mountainous area, and make sure that the plasma display will work where you live.

Many organizations have digital projectors like this one so they can take information that’s on one screen and project that on the wall for many people to be able to see at one time. We usually call these LCD projectors. But the reality is there’s a lot of different technologies that are used today to take that video display and put it on to the screen, not just LCDs.

When you’re using these displays, you’ll notice that they get very, very warm. There’s a lot of heat that’s being blown out of these because the bulb that’s inside of it gets very, very hot. It’s a very bright bulb. And you want to be sure that it continues to be cooled the entire time you’re using this projector. You want to be very careful about that when you power off. Normally, when you power off a projector like this, the fan continues to run to make sure that that bulb cools down properly. If it does not cool down properly, there is a chance you could damage the bulb. And the bulbs in these devices are very, very expensive.

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Category: CompTIA A+ 220-801

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