LCDs vs Plasmas (vs CRTS)

The last line in HD/SD what's it all about was really a throw-away joke, but it seems that it might be useful for another basic differentiation guide*.

First off some background info. Televisions display their pictures using pixels, if you've read my previous entry linked above you'll recall me talking about lines 720 or 1080; each of these lines are made up of pixels. So for a 1920x1080 television they'll be 2, 073,600 pixels that's the same number for a 32" screen or a 40" or a 72" or... well you get the point. Hopefully you'll see that a pixel has no size by itself; if televisions of different sizes have the same number of pixels then each pixel will be a different size. It's important to note this as they might even have a different aspect ratio to the telly.

Each pixel is made up of three sub-pixels Red, Green, and Blue controlling how these sub-pixels are lit determines the colour you see. What makes the types different is how those sub-pixels are controlled.

Refresh rate gets banded about so here we go cinema movies are normally filmed at 24 frames per second (fps), UK TV programmes at 25fps, and US TV programmes at 30fps. Most modern televisions can run at 50 or 60Hz so each frame is drawn twice for a progressive scan or half the frame followed by the other half for interlaced; in HD terms 1080p/50 1080p/60 or 1080i/25 1080i/30. Sometimes you'll see 100Hz televisions advertised these can seem smoother to some people, but remember the input source is still 24/25/30 fps so you're not really getting any additional frames.

CRTs or Cathode Ray Tubes are the old big bulky televisions, they have a tube (hence the name) shaped a little like a cone. At one end is an electron gun and at the other the pixel/sub-pixels made up of phosphor. The gun scans along each line of pixels firing off an electron at some of their sub-pixels; when the electron hits the phosphor it glows.

Plasmas work in a similar way, but instead of an electron gun there's a small fluorescent light behind each sub-pixel, the light flicks on and stimulates the phosphor to glow.

LCDs have one large light shining behind all the pixels all the time and have the equivalent of semaphore gates behind each sub-pixel opening or closing that allows the light to shine through the coloured filter.


Enough tech talk onto what you need to know.

They're getting better but LCDs still have a smaller contrast ratio then plasmas, blacks can appear grey in a darkened room. They tend to have a smaller colour range then plasmas, but again are getting better, and they used to have problems with fast moving images when the pixels couldn't refresh at the speed of the picture. The angle of viewing can be a problem, if you've ever tried looking at a phone or camera display from the side you'll know what I mean. They're also limited size-wise plasmas are much easier to make with larger dimensions so the price per inch can be more expensive.

Plasmas on the other can still suffer from burn-in when displaying a constant image that will leave a ghost image on the screen when you change channels, though they're getting better. They're also heavier then LCDs, not as bright, and use more power. Plasma screens also have a fixed resolution meaning whatever input source you're using will be altered to fit the screen so any 4:3 will be stretched out to 16:9.

So saying all that which is best? Um depends what you want to do with it.

if you want to hook it up to your computer, not after something in the 50" range, are going to be watching it in a reasonably well-lit room, aren't trying to watch it from wide-angles, might be moving it about a bit, or putting it somewhere with poor ventilation -then go for an LCD.

If you're in the dark, putting it in a fixed position with the necessary clearance, want the largest display possible with the largest angle to watch it at, and don't mind that presenters on 4:3 broadcasts appear to have gained weight - then go for a plasma.

Why haven't I discussed CRTs - because despite having the best qualities of both LCDs and plasmas (and some of the faults too) you simply can't buy them any more.

However you may want to wait for the next exciting installment - "Digital tuners in an HD world"

*Basic being the word, don't shoot me if I miss out some technical bits or simplify things.