If I had to name one part of computers that were becoming more popular, it would have to be TFT monitors (also referred to by some people as LCD's or even flatscreens).  However, too many people are buying these and then having problems, so I thought I'd write a little guide to warn you about the differences between these, and conventional CRT monitors (which look like TV's).

Firstly, what are the differences between CRT's and TFT's?  The most obvious one is size.  TFT monitors are very thin compared to CRT's which have a huge depth.  However there are other differences, namely;

• Brightness
• Response time
• Broken Pixels
• Contrast Ratio
• Viewing Angles
• Diagonal Size
• Image Quality
• Non-Recommended resolutions

I will now explain what all the above means, so you can be aware of what to look for, and what to expect when you buy a monitor.

Brightness - This is one area where TFT's beat CRT's.  The brightness of a TFT is typically 250cd/m² whereas the brightness of a CRT is typically 120cd/m².  This means that when you view white's on your TFT, they will stand out much better than on a CRT.  However some of you who are used to CRT's may find a TFT too bright and they will need to turn down the brightness of their TFT monitor. 

Response Time - This is one of the biggest faults with TFT's, however this is starting to become less of a problem.  Basically, TFT monitors have a response time, which is a delay before a pixel (dot of colour) on the screen changes from one colour to the next.  This is measured in milliseconds (ms).  For example, a TFT with a response time of 60ms will take around 60ms for a dot on the screen to change colour from white to black.  This is very poor as the following calculation will show;

1000 (1000ms = 1 second) divided by 60 (the response time of the TFT in this example is 60ms) = 16.66

This means that a TFT with a 60ms response time can show around 16 frames per second.  Now considering your TV shows around 25 - 29 frames per second and your computer CRT shows 60 - 120 frames per second you can see that TFT's are very slow.  This also gives rise to a problem known as ghosting, where the eye can see the TFT screen changing from one frame to the next.  This means that if you are watching for example a plane flying along on a TFT with a very poor response time, all you will see is a blur across the screen where the pixels on the screen are trying to change colour to show the plane moving and you can see the pixels in-between colour changes.  This is why gamers for example wouldn't touch a TFT in the past, as on fast action packed games all you'd see is one big mass of blurriness on the screen.  Modern TFT's are getting better at response times, indeed my TFT has a 20ms response time.  However if you are looking to buy a TFT, I would recommend that you buy one with a response time of 25ms or less.  Otherwise you could well have issues with ghosting. 

Broken Pixels - This is another huge fault with TFT's in that you can get a problem known as Dead Pixels, or Lazy Pixels.  A dead pixel is a dot on the screen which is permanently stuck on white or black.  For some people, this is a major problem especially if you have a black dot permanently located in the centre of the screen.  You can also get broken sub-pixels or lazy pixels which gives you dots permanently stuck on other colours such as green.  Indeed, my TFT screen has a green dot which is stuck on, and that got on my nerves for a while.

Unfortunately, this is a problem due to an imperfect manufacturing process, and therefore isn't a fault of the monitor.  Unless if you have a very large number of dead pixels (usually 5 or more) then their presence isn't classified as a fault and therefore you will not be able to return the TFT for this reason - you'll just have to live with the stuck colours. 

Below are two pictures of what a pixel fault looks like.
Both pictures show a sub pixel stuck on green.  The first picture is an extreme close-up photo of my TFT monitor.

You can clearly see the green dot which should be a very dark blue like the dots around it.

The photo above is a very poor blurry one, but it does show you how this dot stuck on green can stand out.  Unfortunately unless if you can find a retailer willing to allow you to return the TFT if there is a dead pixel on it, there's not a lot you can do if your TFT monitor has one as dead pixels aren't classified as faults.  Fortunately these faults are very small as each dot is tiny.  Therefore they usually don't stand out too much, especially if they are on the edge of the screen.

Contrast ratio - Most CRT's have a contrast rate of about 500:1, so you should ideally look for a TFT which is also 500:1 or better.  My TFT for example is 800:1 and is therefore a very good model to own.  The contrast rate basically tells you how big a difference the monitor can show you between white and black.  A TFT with a contrast rate of 250:1 for example will have a very bad quality black whereas a TFT with an 500:1 ratio will be able to show a much darker black.  I would recommend you look for a TFT with a 400:1 or above contrast ratio.

Viewing Angles - One of the problems TFT's suffer from is poor viewing angles.  This means that if you look at a TFT screen from the side, you might notice that colours are wrong.  For example, a friend once brought his holiday photos round to our house to look at on his laptop, so we all gathered round his laptop to view the pictures and my Dad commented on how he couldn't see the pictures properly - instead he could only see negatives.  Indeed, as my dad was to the left of the screen the colours had been shifted so much he saw the photos as negatives.

The maximum viewing angle of a monitor is usually measured as the angle at which the contrast ratio has dropped to 10:1 of the correct colours displayed when you look at the centre of the monitor.

When you buy a TFT, take a look at its specification.  It should tell you both its Horizontal and Vertical viewing angles in degrees.  For example, a TFT may say it has a 60 Degree horizontal and 60 degree vertical viewing angle.  This means that if you move your head to be 30 degrees to the left, right, top or bottom of the centre of the screen then the colours of the screen will have deteriorated.  This is the part of TFT's which annoys me the most which is why I purchased a TFT with perfect viewing angles (178 degrees) which is perfect since any higher than that and you'd be looking at the side of the screen.  There really is nothing more annoying than you moving your head and seeing all the colours on the screen shift.  You can still buy TFT's today with poor viewing angles (for example 60 degrees) so I really do recommend you look for a TFT with viewing angles of at least 140 degrees and preferably higher.

Diagonal Size - One of the areas in which TFT's beat CRT's is their diagonal size.  You see, CRT manufacturers specify the size of the tube, however some of this is hidden behind the casing and you can't actually see it.  This means that a 15" CRT monitor only has about 13.6" of viewable area.  A 15" TFT monitor however has 15" of viewable area.  This means that a 15" TFT monitor has roughly the same viewable area as a 17" CRT monitor, so if you are upgrading for example from a 19" CRT to a TFT, you only need to buy a 17" TFT to get the same viewable area. 

Image quality - One difference between TFT's and CRT's is the fact that CRT's are Analogue devices whereas TFT's are Digital.  This means that if you plug your computer into your TFT through an analogue cable, you could be losing picture quality as the Digital signal your computer generates is converted to analogue, transmitted to the TFT, and then converted back to Digital.  This means you are also losing quality there.  It would be much better to transmit the signal digitally to the monitor so you aren't losing quality.

However, this matter is complicated by the fact that not all computers have Digital outputs on them.  Some computers are analogue only, whereas others have both analogue and digital.  To find out what sockets your computer has, just look round the back and locate the socket where your monitor is plugged in.  Then compare the sockets around that area with the ones in the below picture to see if your computer has just Analogue, or Analogue and Digital.

If your computer has a Digital socket, then I highly suggest you use it as you will not be losing any quality due to digital to analogue then back to digital conversion. You also won't suffer from the problem that some TFT's have when plugged in through an Analogue connection where black colours shimmer.  However, if your computer has an analogue socket only, then you will need to buy a TFT with an Analogue connection.  You must make sure your TFT has the right sockets on the back to enable you to connect it to your computer.  This is because TFT's come in three types - those with Analogue only, those with Digital only and those with both Analogue and Digital connections.  Obviously if you buy a Digital only TFT and your computer only has an Analogue socket on the back you have a problem.

Non Recommended resolutions - One final problem with TFT's is that they have a recommended resolution which you must use otherwise you will get a problem with scaling errors.  With CRT's, the dots on the screen are created by firing electrons into a phosphor coating.  This means you can create a pixel anywhere you like by firing an electron into that location, therefore you can use any resolution you like on a CRT (providing your CRT supports that resolution).

A TFT however has its pixels fixed in place.  This means that if your TFT is designed to use a resolution of 1024 x 768dpi (dots per inch) and you make it display a picture which is 800 x 600dpi, then scaling will have to take place.  This means that some of those 800 dots will have one pixel representing them and others will have 2 pixels representing them.  This gives you scaling errors where the picture doesn't look right - some parts of the picture are fatter than they should be where 2 pixels have been used instead of 1.  Therefore, when you use a TFT, it is highly recommended you make your windows desktop and all your games run at the resolution your TFT is designed to run at to stop these scaling errors from occurring.

Summary

If this document has put you off buying a TFT, then I'm sorry.  I personally use a TFT and will not be going back to a CRT.  Some TFT's are truly excellent and in my opinion beat CRT's any day.  Plus there is also the advantage that TFT's take up much less room than CRT's.  If you are looking for a TFT, then I suggest you buy one that has the following specifications.

• A brightness of at least 200cd/m² with 250cd/m² being preferable.

• Horizontal and Vertical viewing angles of at least 140 degrees or higher.

• A response time of 25ms or less.

• A contrast rate of at least 400:1 or higher (e.g. 500 to 1)

You also need to make sure your computer and the TFT you are buying have the same type of socket, and if you have a Digital socket on your computer I recommend you use it and buy a TFT with a Digital socket.

If you are looking for some recommendations for TFT's then I personally love the Samsung range of TFT's.  They are all nice and slim, and there is a good range of reliable models.  If you are a gamer, then you want the Samsung 172x which has a 12ms response time to minimize ghosting.  If you aren't too worried about ghosting or don't play a lot of games, then other Samsung models will do you such as the Samsung 172v.  I should point out that I don't work for Samsung at all - I merely like their range of TFT monitors and I myself use a Samsung 193p. 

If you have any comments, or queries about this article, then email me by clicking on the envelope picture on the bottom right of this page.