Display devices 000 021 a computers primary output

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Display Devices 0:00-0:21 A computer's primary output device is its display. Videos, photos, emails, web pages, practically everything the computer processes is eventually output on the display device so in this lesson, we're going to take a look at the different display devices that computers can use, and the technology behind them. Liquid Crystal Display (LCD) 0:22-0:41 The first display device we need to look at in this lesson is the liquid crystal display, or LCD. Now LCDs are a type of flat panel display that use liquid crystal technology to display visual information. Let's take a look at the different components that make this possible. The first component we need to talk about is the screen itself. LCD Screen 0:42-2:41 Now LCD screens are composed of several layers. If we were to look at a cross-section of an LCD screen, it would probably look something like this. Starting from the bottom, we have a polarization panel, then a layer of thin film transistors, or TFTs, then a layer of liquid crystals, then color filters,and then another polarization panel. Now LCDs are not capable of illuminating themselves so they have to have a special light added to the display called a backlight that shines through the screen so that we can see it. Now when the light from this backlight passes through this bottom panel, it becomes polarized. This essentially means that it's moving in a specific direction. Now the outer polarization panel here only allows light to pass through in a specific direction, which is perpendicular to the polarized light. This means the polarized light here will be blocked by the outer panel unless its direction is changed. This is where the liquid crystals and the TFTs are used.Each TFT is able to apply a specific voltage to the liquid crystals. When no voltage is applied, the liquid crystals are aligned like this. This orientation twists the light and allows it to pass through the outer panel as red, green, or blue light, depending upon the filter the light went through. But when voltage is applied, the liquid crystals align themselves like this, straight up and down. Now this orientation doesn't affect the light so it's blocked by the outer panel, creating a black pixel.The liquid crystals also react to partial voltage. For example, if half the voltage is applied, then the crystals partially align and only let 50% of the light through. Really, one way to think of this process is to compare it to a window blind. When the blinds are open, they let all the light through the windowbut as you close them, they let less and less light through the window until they block all the light altogether. By controlling the amount of light that passes through each panel, controlling its luminosity, LCDs are able to produce RGB color and display visual content.
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