Plasma TVs have long had the best contrast ratio and picture quality in the HDTV market. But with recent advances in LED TV technology, plasma has been losing its advantage.
How Plasma TVs Work
Plasma TVs rely on bubbles of gas and mercury trapped in a grid. Behind that is an array of electrodes that pass electricity into the pockets of gas. When the electricity flows into the bubbles, the mercury is vaporized and the gas becomes plasma that glows at ultraviolet wavelengths. These ultraviolet emissions are not visible to the naked eye, so phosphor is coated on the outside of the bubble. When the ultraviolet light hits the phosphor, it begins to glow. In this way the plasma TV is similar to older tube televisions. Both technologies rely on phosphor to create the image, only the method used to energize it is different. This technique makes extremely crisp images, thanks in part to very high refresh rates.
How LED TVs Work
LED TVs rely on a traditional LCD panel like you would find in your computer monitor. An LED backlight is then used to light up the image. The backlight can either be full panel or edge lit. Edge lit panels distribute the light evenly throughout the TV, relying on the LCD panel to blot out the black parts of the image. This technique is both cheap and thin. A full panel backlight, on the other hand, has much in common with a plasma TV. An array of LEDs is connected to control circuitry that can handle it, in much the same way that the array of electrodes in the plasma TV works. But historically LCD screens have suffered from blurring of the image, due to low refresh rates. But modern LCD panels have largely fixed this problem.
Plasma has always had a few disadvantages over LCD TVs. They are heavy, for one. LCD TVs are thin and light, not needing much material in order to function. Plasma screens need large sheets of glass in which to sandwich the gas and mercury, in addition to any framing and control hardware. They also blurred action in fast paced scenes. Also, if you see the same scene displayed for a long time, it can get burned into your TV. LCD panels don't have this problem.
Full Panel LED Backlights Fix LED TV's Problems
LCD TVs have not had the same contrast ratio of their plasma counterparts, however. Because most were edge lit, the entire screen had a uniform glow which it was up to the LCD panel to blot out. Full panel LED backlights don't need to worry about this. They can selectively choose not to light certain sections of the screen, just like plasma screens can.
Plasma has historically been the leader in image quality. But the technology has been pushed about as far as it can go. LED TVs are still advancing. Right now, if you had to choose a winner in the LED vs Plasma TVs debate, it would be LED by a small margin. But it won't remain small. Soon LED TVs will be far better, and plasma TVs will be extinct.