An Overview of Display Devices – CompTIA A+ 220-901 – 1.10

We rely on display devices as the primary output from our computers. In this video, you’ll learn about LCD displays, plasma technology, digital projectors, OLED displays, and more.

<< Previous: Designing Custom Computer SystemsNext: Display Specifications >>

If you’re watching television, or looking at a computer screen right now, then you’re probably looking at an LCD display. LCD stands for Liquid Crystal Display, where light is shining from a back light through liquid crystals and ultimately a colored filter to be able to show you this information on the screen.

LCD displays work at the molecular level, where the liquid crystals are being twisted so that they will shine light through polarizing filters. It’s something that occurs very quickly, and on the screen we simply see moving images. There’s a lot of activity that’s happening on the inside of your LCD display. To be able to see light through these liquid crystals you need to be able to shine the light from the back side of it. So there’s usually some type of backlight behind the screen itself. And when the liquid crystals are twisted, that light is able to shine through.

Here’s a microscopic view of what this LCD display is doing. We have a backlight on the right side that is shining a light through the LCD monitor, and we’re able to see what’s coming through here on the left side. You’ve got these vertical and horizontal filters. So when you’re twisting this crystal molecule, it allows the light to now pass through these glass plates, and ultimately through a color filter that will finally turn into the image that we’re looking at on the screen.

You’ll generally see two different kinds of LCD technologies out there. One is the TN, or the Twisted Nematic LCD. This is a very common LCD screen that you’ll find on many different LCD displays. If you’re a gamer, you’ll like the TN LCD because you’re able to get very fast response times, down to the one or two millisecond level. This also is not using a lot of power for the TN technology.

Unfortunately, it has a very small viewing angle. If you ever look at the edge, or to the side of a TN LCD, you’ll notice that the color inverts itself. You’re able to see that the shifting of color might have a very narrow range, so you have to be right in front of the TN LCD monitor.

The other kind of LCD monitor you’ll find is the In Plane Switching, or the IPS LCD. These provide a very good representation of color. If you’re someone who’s working with graphics on your screen, this might be the monitor you want to use. These are also good for mobile devices because if you touch the screen, they don’t distort or tail the color as you’re moving your finger. But these are a bit more expensive to produce, so we tend to see more of the TN LCD on the lower end systems, and the IPS LCD’s on the higher end systems.

To be able to view the image that’s coming through the LCD, we need to have some type of light that’s behind the screen. This backlight can be one of two different technologies. One that we don’t see much of any longer, but you may see it on some older monitors, is the CCFL backlight. That stands for Code Cathode Fluorescent Lamp.

This is going to require some additional power over what is used today with an LED backlit display. It also requires a power converter because the backlight for a fluorescent lamp needs AC power, and we’re usually giving the components inside of the monitor DC power. So it has to convert that using the power inverter. This will also add a bit more thickness to the display because the fluorescent lamps need a bit more room. Because of all of these reasons, we tend to use other technologies for backlights today.

The technology we use today is using LED’s instead of fluorescent lamps. You’ll sometimes see these referred to as LED monitors. What it really is is an LED backlight LCD monitor. You’ll sometimes see the LED lights will be put around the edges of the displays, but when you have these larger monitors or televisions, you’ll see ranges like this where the LED lights are separated and put throughout the entire back of the display. This can provide some interesting capabilities, especially if you’re watching a movie that has very dynamic lighting because then the television can light and dim different parts of the screen at the same time.

A legacy display type you may still see in use is the plasma display. This is a series of very tiny cells that contain noble gas and mercury. And when you add voltage to that combination, you get UV light. That light is then sent through a colored phosphor, and so we’re able to watch a movie, or watch a sporting event, by seeing all of these tiny dots of light displayed on the screen. This gives us some very nice black colors, and we also have very fast response times on a plasma display. Because of the improvements in LCD technologies through the years and the improvements in the cost of LCD displays, we don’t tend to see plasma displays produced any longer.

If you’ve ever been in a corporate conference room, or you have your own home theater, you might be using one of these digital projectors to display information. These are often using an LCD– and we sometimes refer to these as LCD projectors– although the technology behind the scenes is not always using LCD. An important part of this technology is the ability to project this video onto a wall. And to do that, you need a very bright, and ultimately, a very hot lamp inside of these devices.

These lamps can be very expensive to replace. They could range anywhere from $35 up to over $350. Because of that, if you’re working with a digital projector, you want to be sure that you let the bulb completely cool off before turning off or unplugging this device. Whenever you turn off the lamp in these digital projectors, you’ll notice there will be a fan that continues to run, so that it can gradually cool down that lamp, and it’ll be available to use next time you turn on that projector.

OLED stands for Organic Light Emitting Diode. There’s very small diodes of organic material inside of these displays that will light up when you provide current. They’re very thin and very light. They have a flexible material that doesn’t require any glass, and you’ll notice there’s no back light with these. When you provide the current, the organic material itself is providing the light source. However, these organic materials can degrade over time, so you’ll find that the overall lifespan of an OLED display will be a bit less than that of a traditional LED display.