Display Specifications – CompTIA A+ 220-801: 1.10

| October 15, 2012


When you are selecting a display device, there are a number of specifications you should consider. In this video, you’ll learn about refresh rates, native resolution, display filters, and much more.

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A common specification for displays is one called refresh rate. This refers to how often the information on the screen is updated. It’s usually referred to as the number of times in a second. And that’s also referred to as Hertz.

On CRT displays, this refresh rate was one we measured by how long it took the electron beam to paint everything on the display. That beam had to go line by line on the entire screen. And so it had to work very hard when the resolutions and the screens got much larger.

Whenever we saw the refresh rate drop below 72 Hertz or somewhere around there, especially for the really large displays, the human eye started to see flickering. And it got to be very annoying when you are watching the monitor. So one of the things that was important that you had a display that could support the resolution you needed at refresh rates that were somewhere above 72 Hertz and higher.

Obviously today, we aren’t CRTs, but we’re still using the term refresh rate. On an LED display, these flat panels that we currently use, the screen updates immediately for every pixel on the display. And almost all LED, LCD-type displays are updating the screen about 60 times per second. Because we’re not writing information from the top line and all the way down the screen and starting over again, we don’t have that flickering that we would see by the human eye. Instead, we’re simply updating every pixel all at the same time and generally 60 times a second.

Regardless of the type of display you have, one important specification for displays is the resolution of the display. This is usually represented by the width, the number of pixels wide, versus the height, the number of pixels high. This is really referring to a pixel dimensions, regardless of the size of your screen. It’s the total number of pixels in each direction.

If this was an XGA screen for instance, it would be 1024 pixels wide and 768 pixels high. For SXGA, it’s 1240 by 1024 and by UXGA, we mean that is a 1600 by 1200 pixels. This displays a good representation of all of these different types.

And for most purposes, you don’t have to memorize all of these. But it’s important to know how this has changed through the years. For instance, the early CGA displays were 320 pixels wide by 200 pixels high. And these days you can compare it to some of the larger displays like this WQXGA that I use that is 2,560 pixels wide by 1,600 pixels high.

When you’re working with LCD displays, an important specification is the native resolution of the display. When we were using CRTs and we changed resolutions, it could simply change what it was presenting on the tube that was in front of us. But LCD displays can’t change the number of pixels that they have. They will always have a certain number of pixels wide and always have a certain number of pixels high.

But we often like to change the resolutions that we use on our computers. And so our LCD displays have to adjust themselves to try to make it look best for the number of pixels that might be on the screen. And if there is a mismatch of the number of pixels wide and high, you might see something like this, where some of the letters look a little thinner or a little fatter as the display tries to fit in exactly what it should be displaying to you at that particular resolution.

If it is looking like this, you might want to try changing the resolution to something that is either the native resolution of the display or some type of multiple of the native resolution. For instance, if the LCD monitor is one that is 1600 by 1200, you might want to change it to 800 by 600 because it can easily take the pixel density and just divide it by two.

It’s very important that our displays are able to show us a very clear view of what we’re displaying. And so we want to look at display brightness very carefully. One measure to look at is the luminance. This is the candela per square meter. You may see this as CD/M2. The brighter it is, the higher that number will be and generally the better quality screen we’re going to have on our display.

Another measure is the number of lumens. This is used a lot for digital projectors. If it’s one that provides 3,000 lumens, it tends to work very well in a dim room. If you have one that is able to put out 6,000 lumens, it’ll work pretty well even if you aren’t covering up all of the light coming in from outside.

Another important measurement is the contrast ratio. This is the measurement between the blackest black compared to the whitest white. We want the widest range. We want the biggest ratio between those things. The larger that ratio, the higher the quality of the picture.

Our video signals may be sent from our computer to our display a lot of different ways. One way is via an analog signal. Something like a VGA display like this one will send a simple, continuous analog signal from our computer to our monitor.

Sometimes you’ll notice if you have a very, very long VGA display and you plug-in, you’ll notice you’ll get go staying on the picture. And that’s because we’ve lost signal. We’ve lost some of that analogue signal between our computer and the display that we’re plugging into. That’s usually transmitted via this VGA interface, this DE-15 interface that we have on our computers.

Many modern monitors are using a digital signal to provide that video display. Something like a DVI port can provide digital output. That’s a Digital Visual Interface. Or something like the very common HDMI interface that can output to a computer monitor or even to a commercial television screen.

Either one of these display connections can provide you with that digital output. You just want to be sure that if you’re going to extend that signal over a long cable, that it’s able to get that signal all the way from your computer, all the way through the cable, and finally to your display device.

Many people will also add filters to their displays. One very common filter to see, especially if you’re in an environment where security is important, is something like a privacy filter. These are filters that you can put on the outside of your display, whether it’s a desktop display or a laptop display. And this becomes something that you can see very clearly when you’re looking straight on. But as soon as you change this to be an angled view, your screen turns black or gold.

I’ve seen this work in an airplane where the person next to me is working on their computer. But I can’t see anything on their screen. It’s completely blacked to me. So that’s great to use if you’re someone who’s traveling a lot or you’re in those high security environments.

Another common filter to get is an anti-glare filter. Today, our monitors tend to be very glossy. So one of the problems we have is that the ambient light that’s around us will reflect off the screen and make it difficult to see what’s going on. By using these anti-glare screens, we can reduce the glare, and thereby see what’s on the screen a lot easier.

I use multiple displays on my workstation. And it’s a great way to work. You can have information shown on one screen, have a completely different group of things shown on the other screen, and easily move things back and forth between them. It makes it very, very flexible to work. Some people will take that and extend the desktop across like I do, so that you can put different applications in different places on different screens.

Some people will also mirror the desktop. You see this if you’re presenting to a different group of people. You can plug in your mobile device to an existing monitor and they’re seeing exactly what you’re seeing on your screens, that you can then present to a larger group.

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Category: CompTIA A+ 220-801

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