Three of the most popular types of high-definition televisions are plasma, LCD and LED. Plasma TVs tend to be the brightest, but LCD and LED TVs are usually more energy efficient and thinner.
The picture in a plasma television is generated when ionized gas (plasma) reacts with electrodes stored between two thin layers of glass. This reaction is self-illuminating, so no backlight is required and the image is bright with high contrast levels. However, plasma TVs are not as energy efficient as LCD or LED TVs, or even some standard definition sets. Plasma TVs also are restricted by size; they cannot be smaller than 42 inches and do not work at altitudes above 6,500 feet.
LCDs also use two panes of glass (or other transparent material), but instead of gas, a thin layer of liquid crystals is stored. The LCD generates the image and color of the display, but the image needs a backlight to be visible. LCD TVs use cold cathode fluorescent lamps to do this. CCFLs are more energy efficient than plasma displays and can be used on TVs of all sizes, but the edges and corners of the display are usually dimmer than the rest, and the contrast and black levels can be lacking when compared to plasma displays.
An LED TV actually is an LCD TV. The difference is that the TV uses LED lights instead of CCFL lights. While CCFLs are long tubes that go across the entire TV screen, LED lights are small, individual lights that are laid out in an array. Only the lights that are required for each picture are used, so contrasts are higher with deeper blacks. Because LED lights are smaller than CCFLs, LED TVs tend to be thinner and more lightweight than LCD TVs.