High Definition (HD) basically improves the quality of the picture (approx. 4x better) and manufacturers are continuously trying to improve the picture quality. You may say "I'm happy with the image I have already" but wait till you see anything in HD then you will not want to go back to Standard Definition. Films and documentaries come to life when you have your television set up properly.
Reasons to buy an LCD or Plasma:
If you want to watch HD content
If you think they look nice in your living room and want to save space.
Do not buy one if you think that because LCDs and Plasmas are newer technology the picture will automatically look better. In fact, if you are only going to be watching normal TV then in most cases the old fashioned CRT TVs will still be your best choice for picture quality. However, if you want to watch HD then you need an LCD or Plasma.
HD LCDs and Plasmas have a higher number of pixel lines of resolution, hence the name High Definition. Full HD is currently 1920x1080 lines. If you are only going to be watching normal Pal tv (Terrestrial, Freeview, non-HD Sky/Virginmedia) then this resolution is 720x576. Therefore this image resolution has to be 'uprezzed' to fit on the HDTV - i.e. pixel lines will have to be duplicated. Imagine you have a photo that looks fine small but if you want to blow it up to poster size, the quality will reduce. Obviously, good quality TVs such as Sony and Samsung have invested in good 'uprezzing' technology therefore the picture still looks very good but you pay more for this.
Once you've decided that flat screen TVs are for you then which type do you get?
Get an LCD for HD through Sky or Virginmedia on 42" or less.
Get a full HD Plasma TV for Blu-ray or HD-DVD 42" or more, if you can afford it.
There will be exceptions to these rules - the main one being this: Some Plasma TVs that offer smaller resolutions have such a great contrast ratio that the picture quality is still good. But in general my rule sticks - High Definition means higher resolution and if the TV doesn't have it then you're not getting true HD, no matter how good the 'uprezzing' is in the TV.
Size of Screen: If you want a big screen (i.e. 42'' or more) then I would go for Plasmas. Bear in mind though you also need a big room to appreciate that size. Anything less than 42'' then something called bleeding can occur in Plasmas. That is when the image colours start to mix in with adjacent colours. Finally, if you want to enjoy HD don't get a TV less than 32 inches as you are not really enjoying the benefit of HD.
Contrast Ratio: Well Plasmas in general are better for contrast ratios (5,000:1 is a good ratio). This is often thought as being the crucial aspect in picture quality. However, there is another aspect that is of importance.....pixel resolution.
Pixel Resolution: Basically the higher the number of pixels the better picture you get. However, you may be paying unnecessary amounts of money for bigger resolutions when the picture being broadcast is smaller, as mentioned earlier. Out of interest I believe at present Sky and Virgin broadcast HD at 1440 x 1080 (this is to save on bandwidth). Therefore the only way to see full HD at 1920 x 1080 is via a Blu-ray or HD-DVD player or PS3. These all output at 1920 x 1080.
Refresh Rate: This is only important if you like watching fast moving images on your television, like Formula 1 etc. If you do, then get a 100Hz TV. Otherwise I personally wouldn't worry too much about this.
Progressive or Interlace: This describes how a picture is filmed and displayed on your television. Normal home video cameras (i.e. DV cameras etc.) shoot interlace. Old TVs (CRTs or Cathode Ray Tubes) display the image interlaced.
CRTs have 720 lines of vertical pixels and 576 lines of horizontal pixels. In the UK (i.e. Pal) it takes 1/25th of a second to display all 576 lines. It does this by displaying 288 alternate lines in the first 1/50th of a second and the other 288 lines in the second 1/50th of a second, therefore taking 1/25th to display all the lines. LCDs, Plasmas and film are inherently progressive. This means that the image is captured and displayed in one pass. Each line is displayed at the same time. Most people (including the sales advisors in the shops) are unaware that LCDs and Plasmas do not display interlaced images. If something is shot interlaced and is shown on an LCD or Plasma, the TV will de-interlace it and display all the lines in one pass (1/25th of a second).
THEREFORE, PROGRESSIVE OFTEN MEANS BETTER PICTURE QUALITY, as progressive gives a higher resolution at any one moment in time. However, at present all broadcasts are interlaced (to save on bandwidth.) Therefore the only way to benefit from an HD progressive TV is by watching a Blu-ray disc.
1. Get a plasma for large screens (42'' or more) with a good contrast ratio.
2. If you don't have Sky HD, Virginmedia HD or a Blu-ray/HD DVD player then there is little point spending extra money on a television that has full 1920 x 1080 resolution when you will not see the benefits.
3. Don't worry too much about refresh rate if you are not watching many fast moving pictures (i.e. if you mainly watch dramas, I wouldn't spend an extra £100 for a higher refresh rate.