How CRT and LCD monitors work

Written by Wil Harris

March 20, 2006 | 11:53

Tags: #backlight #crt #diode #lcd #led #monitor #oled #sed #technology

We all spend an awful lot of time sat in front of computers. Whether we're gaming or working, we are at the mercy of what many would argue is the most important element of any system - the monitor.

A well-defined monitor can make using a system a pleasure. Likewise, being forced to squint at a 15" CRT at 60Hz can make us weep in pain and long for a nice LCD to while away our hours at. A good display makes all the difference.

Monitors are widely used and rarely understood. Sure, you know that the difference between LCD and CRT is that one is flat and one is massive and heavy. But do you really understand the technology that goes into these things?

In this article, we're going to investigate how CRTs and LCDs work, and also examine some of the issues pertaining to monitors, such as Refresh Rate and Vsync as well as looking into our crystal ball to see the future of displays.

For a primer on resolutions, you might like to check out our previous article here.

How CRT and LCD monitors work Introduction How CRT and LCD monitors work Introduction

The Basics

So let's start with the easy stuff. The picture that appears on your monitor comes from the graphics card in your computer, and the job of the graphics card is to render the picture suitable for the monitor. A wired output runs from the graphics card to the monitor.

But you knew that already.

Both the graphics card and monitor adhere to the same set of specifications, so that they can happily talk to each other. The standards are set out by VESA, which defines things like how monitors identify themselves to the computer.


CRT stands for Cathode Ray Tube, and is descriptive of the technology inside that chunky monitor you might have on your desk.

CRTs receive their picture through an analogue cable, and that signal is decoded by the display controller, which handles the internal components of the monitor - think of it as the mini-CPU for the monitor.

CRTs have a distinctive funnel shape. At the very back of a monitor is an electron gun. The electron gun fires electrons towards the front through a vacuum which exists in the tube of the monitor. The gun can also be referred to as a cathode - hence the electrons fired foward are called Cathode Rays.

These rays correspond to to the red, green and blue channels of the display and video card.

At the neck of the funnel-shaped monitor is an anode, which is magnetised according to instructions from the display controller. As electrons pass the anode, they are shunted or pulled in one direction or the other depending on how magnetic the anode is at that time. This moves the electrons towards the correct part of the screen.

How CRT and LCD monitors work Introduction
The electrons pass through a mesh, and this mesh defines the individual pixels and resolution on the screen. Electrons that pass through the mesh then hit the phosphor coating which is on the inside of the glass screen. When the particles hit the phosphor, they immediately light up - causing the light to shine through the front of the monitor, thus making up the picture on the screen. There are three differently coloured phosphours for each pixel (known as phosphor triads), and depending on which phosphor the electron hits, that's which colour the pixel will light up.
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