How a Plasma TV works

A current, applied between the two electrodes at a given intersection, introduces a stream of free electrons into a gas chamber, which collides with gas atoms and knocks free more electrons. The gas becomes plasma, particles collide and energy is given off in the form of photons.

It is these photons (most of them ultraviolet and therefore invisible to the human eye) that in turn excite the phosphors and make them generate energy as light - but this time the light is visible.

Depending on the characteristics of the original electrical charge the photons will emit more or less intense light, and along with the combinations of red, green and blue cells there is enough material to create a TV picture with millions of colours.

Although this all sounds rather cumbersome, the transitions from gas to plasma and back to gas take place so rapidly that the pixels can easily be manipulated quickly enough to produce a smooth, highly watchable image, but there is a problem with the process...

Poor contrast has been an Achilles heel for plasma screens that is, thankfully, being addressed. The problem stems from the need to keep the gas chambers 'primed', that is, to keep a low current running through them constantly.

Without this priming, the process of activating the cell would take too long. The time it takes for a cell to go from inactive to active and back to inactive is known as the 'response time' and a response time that is too slow will impact on picture quality by introducing blurring. Consider how long it takes a fluorescent light to illuminate when switched on and you will have an idea of the potential effect of a poor response time.

Priming increases the responsiveness of the gas chambers - in effect it keeps them in a state of readiness - but it also results in them emitting a low level of light even when they should be inactive. This impacts on contrast. Early plasma screens had contrast ratios as poor as 70:1, while some manufacturers now claim ratios of 3000:1, with corresponding improvements in image quality.

Eventually it is expected that plasma response times will reach the optimal level of 15 milliseconds, which is the sort of level a CRT set is capable of.