When does a television become HD? 'When it's ready and enabled to display high definition signals' would be the obvious answer, but this is somewhat non-descript and electronically it goes a lot deeper than that.

A television screen or projector lens that is HD enabled has a higher resolution than that of a standard TV. This means that the lines which go across the screen are able to be closer together whilst still projecting the image. Because they are closer together, the pixels between them are smaller and there is space for a lot more detail in the image. The reason that most HD television sets are Plasma or LCD (Liquid Crystal Display) is that they can display the greater amount of information sent to the screen with their lines which are closer together.

Regular television screens have a maximum resolution of 480p (NTSC), or 576 (PAL), which means any HDTV is around double the quality of a standard one. There is also ten times the amount of pixels displayed on an HD screen than a standard screen at any time; thus greatly improving the quality of the picture.

The label 'HD ready' that you see on televisions and projectors means that the screen has a resolution of 1080p, 1080i or 720p and comes with an HDMI or DVI cable. The other two products that are needed to make HD work on your TV are up to you to find and these are an HD set top box and an HD service such as Virgin Media or Sky HD. If you're missing one or more of these components then your HDTV set won't work and the image will appear exactly the same as it would on a standard television.

If you're left wondering what the p's and i's stand for then the explanation is quite simple. P stands for 'progressive' and I stands for 'interlaced'. With a progressive scan mode each line is enabled vertically one after the other, whereas interlaced scans the data onto the screen firstly with all the odd lines and secondly with all the even ones. The differences between the two are that the progressive mode is better suited to movement and interlaced mode delivers the data to the screen very quickly.

To summarise, an HDTV is one which delivers a higher density of pixels to your screen and therefore a better quality picture as you watch. There is a lot more room for intricate detail which results in real life images having more natural lighting, smoother movement and a greater sense of depth. Watching your favourite programmes on an HDTV is, on the whole, a much more realistic feast for the eyes.