Inner Workings: Inside a Plasma Screen

When a plasma TV isn't displaying an image, the stuff behind the name is just an inert gas - usually a mixture of neon and xenon - but it's a big part of what allows these TVs to measure just 3 to 6 inches thick.

Unlike a bulky tube TV, a plasma display uses a combination of thousands or even millions of discrete pixels to form a picture. A plasma with a resolution of 1,024 x 768, for example, has 786,432 (1,024 times 768) pixels. If that sounds like a lot of dots, it's really just a third of the story. Each pixel is actually made up of three separate sub-pixels: one each for red, green, and blue. (Next time you're near a plasma, put your nose up to a white area - you'll be able to see all three sub-pixels, and smell that new-plasma smell.)

The sub-pixels, also known as cells, are basically tiny pockets filled with gas. The inside of each cell is coated with red, green, or blue phosphors, like the ones that line the inside of a traditional picture tube. Using phosphors allows plasma TVs to closely mimic the color palette of tube TVs - but it also makes them vulnerable to burn-in, which is basically uneven phosphor wear.

As you can see from the illustration, each cell has a pair of electrodes associated with it - one in the bottom of the cell and one above - arranged in two layers of glass substrate. The top electrode layer is transparent - you actually look through it to see the picture. When current is run through the electrode layers, the gas inside each cell is excited into an ionized plasma state that releases ultraviolet photons. Those photons react with the phosphors, producing reds, greens, or blues of various intensities. The combination of colors in each complete pixel can produce millions of real-world colors, from white to black and everything in between.

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