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Displays
by John Anthony


LED Display
LED (Light Emitting Diode) displays have found their way into monitors for desktops, laptops, tablets and smartphones and now are the predominate technology used for computer monitors.

An LED display is an array of light emitting diodes each of which is used a as pixel (picture element) in the display.

LEDs are bright and are very energy efficient compared to competing display technologies.
They can be switched on and off quickly which provides for very good light control.

A 1080 display has a screen width of 1920 pixels and a screen height of 1080 pixels.

1080i vs. 1080p

1080i indicates an interlaced sweep (a holdover from CRTs) which first sweeps of all the odd lines followed by a sweep of all the even lines.
A 1080p display uses the same number of pixels with a progressive sweep which scans all lines in order, 1, 2, 3 etc.

LEDs are also used in flat and curved screen TVs, traffic lights, store signs, billboards, some automobile lights.

LCD Display
LCD (Liquid Crystal Display) were the technology used in laptops for some time, and later on migrated into displays used for desktop PCs.

In the early 2000's they become the predominate technology used for computer monitors helping to push CRTs out of use.

The text and images in an LCD are created by a back light behind the panel, that shines through pixels (picture elements). Each pixel is made up of three chambers red, green and blue. The chambers in each pixel must be opened enough and in the proper proportion to produce the correct brightness and color.

For an LCD to provide a screen resolution 1024 x 768 pixels (SVGA), it must have 786,432 (1024 x 768) pixels. In TFT (Thin Film Transistor) type LCDs, each pixel is controlled by a tiny transistor that opens and closes the chambers in each pixel.

Desk top LCD displays are powered by standard 120Vac wall power.

CRT Monitors
Before LCDs edged them out CRT (Cathode RayTubes) were the only type of displays for use with desktop PCs. They are relatively big (14" to 16" deep) and heavy (over 15 lbs).

They are available in screen sizes from 14" to 21". A 17" display means that it is 17" measured diagonally from one corner of the tube to the other. The actual viewing area is smaller than 17" (about 16") since the electron gun can't sweep completely to the tube edge.

CRTs send a stream of electrons to the back of the screen, which is charged to about 25,000 volts. As they strike the screen they cause green phosphor on the backside of the screen to glow creating light which you see. The electron stream is sweep back and forth and up and down at about 60 sweeps per second and turned off and on at the right time to make text and graphics images appear.

They are powered by standard 120Vac wall power.

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