How LCD and Plasmas work at the pixel level
Tony Sarno17 August 2007, 11:44 PM
To really understand the unique properties of plasma and LCD TVs, it's worth looking at the fundamental differences between the two at pixel level.
To really understand the unique properties of plasma and LCD TVs, it’s worth looking at the fundamental differences between the two at pixel level.
Plasma at the pixel level
 : How a plasma pixel works |
Each plasma screen has millions of tiny cells containing an inert gas. In each cell there are three sub-cells, with red, blue and green phosphors. When a charge is applied to the gas in each sub-cell, the gas turns into a plasma which causes the phosphors to glow, thus creating the image. A plasma screen is more like an old CRT screen, since the images are created by excited phosphors. As a result, plasma HDTVs can generate more colours (billions vs 16.7 million for LCDs). They can also create darker blacks, simply by not activating the phosphors in the dark part of the image - or, if we use a torch analogy, by switching the torch off.
LCD at the pixel level
An LCD screen essentially shines a backlight through a layer of liquid crystals which – when voltage is applied - twist to let varying amounts of light pass through colour filters, to eventually create an image on the screen . Coupled with the fact that LCD pixels can be made smaller than plasma pixels, this backlighting characteristic makes LCD screens generally brighter and crisper than plasma screens. The downside is that the blacks are not as dark as those generated by plasmas because even when the liquid crystals are polarised to block the light, some still gets through. It’s like turning off a torch by putting your hand in front it.
The faceoff