Buying a Monitor

The first choice to make CRT or LCD

The first choice you will have to make when you have decided to purchase a new monitor is what type of monitor you are looking for. The two main choices are CRT (Cathode Ray Tube) and the LCD (Liquid Crystal Display) some LCD monitors may be referred to as TFT (Thin Film Transistor), these are higher quality LCD displays that use an active matrix, more on this later.

The CRT monitors are a cheaper solution and can be purchased in much larger sizes and with higher resolutions than their LCD counterparts.  The advantages of the LCD screens is that they are flat screens and require no tube. This means that they have a very thin casing and don't take up much space on the desktop, they are also favoured for there sharp picture quality and lower power consumption. This is why they used to be only found in notebooks and laptop computers. Now the price has come down many people are choosing to go with LCD/TFT screen on there desktop machines.

How does a CRT monitor work?

Cathode Ray Tube monitors work by firing charged electrons at a phosphorus film. When electron hit the phosphor it glows creating the light you see.

The electron gun or cathode is used to create a stream of electrons called a ray. This thin beam of electron is directed at the phosphor screen and controlled by deflection plates. In order to steer these electrons to hit the correct place on the screen a magnetic field is created at certain strengths. Copper wire wound tightly is used to create this effect. There will be two sets of wires inside the CRT, one to control the horizontal and one for the vertical deflection of the electron beam. This high speed deflection will light up each pixel on screen in turn.

That was the basics of a simple CRT. This however will only create a black and white picture. To add colour we need to add two more electron beams. We can call these the Red, green and blue beams. In order to make colour we also need 3 sets of phosphor. Again a green, red and blue sheet is required. The phosphor is arranged in stripes of each colour and a single beam is aimed at its own colour when required. A single pixel will have all three colours behind it and so the mixture of the coloured glows from the phosphor will create the colour you see on screen.

How does an LCD monitor work?

Liquid Crystal Displays are a completely different kettle of fish. A liquid crystal you may think is an impossible state to be in, however the liquid crystal exists in the form between a solid (crystalline) state an a liquid. It is this that is the key to LCD monitors as you will find out soon. The big difference between a CRT and a LCD monitor is the way that they create the light on the screen. A CRT monitor has phosphor to create a glow, LCD technology on the other hand is always lit up, it uses liquid crystals to block the light rather tan create it.

The basics here are that a liquid crystal is twisted in such a way that only a certain light source can pass through it. An electric current can untwist the crystal and therefore blocking the light source. To learn a lot more on LCD technology we recommend looking at this article from how stuff works which will tell you all you need to know about LCD's

There are two types of LCD screen, passive and active matrix. The passive matrix screen is very simple. A grid of thousands of transistors with liquid crystals is set up and a charge is sent down to each pixel individually to get the desired effect.  Problems with this include a slow response time, being you may get ghosting patterns on your screen as well as subsequent liquid crystals getting a partial charge and making slight blurring effects.

The most commonly used and best form of LCD screen is the TFT (Thin Film Transistor) The TFT screen is a form of active matrix. Active matrix screens have a transistor and capacitor for each pixel. The capacitor is able to hard the correct charge until the next refresh also only the exact pixel will receive the charge and so the effects are much better on screen. By sending an exact charge most LCD screens today will have a 256-greyscale just by altering the voltage to each liquid crystal in very small increments.

In order to get colour into the screen, each pixel must have 3 sub-pixels. Again these are red, green and blue. By being able to get 256 shades of each of these colours we get 256x256x256 which is nearly 16.8 Million colours.

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