LED TVs are a member of the LCD TV family from the technical viewpoint. The screen of a LED TV is a liquid crystal display similar other LCD TVs. The main difference between the two is the different backlighting techniques which change the picture quality characteristics dramatically.
While normal LCD TVs use so called cold cathode fluorescent lamps (CCFL) for the backlights, LED TVs use light-emitting diodes instead. The result of using LEDs is a bigger dynamic contrast, which means darker blacks and whiter whites. Especially black very often appears as a dark grey on regular LCD TVs. Since LEDs are very slim this leads, in most cases, to a slimmer TV as well. They are also saving a lot of energy compared to CCFLs and often stay below the Energy Star seal requirements, which positively influences your electricity bill as well. There is less pollution when recycling them, too.
LEDs have small disadvantages as well, depending on the dimming method. While top of the line televisions tend to use the new precision dimming feature often referred to as local dimming, older models are edge-lit only. Still better than the CCFLs, but the illumination created this way isn’t perfectly homogeneous.
Always keep in mind that the quality of the display, no matter if LCD or LCD with LED backlight varies alot, depending on size and manufacturer. It’s always recommended to check an electronics store close to you, even if you are planning on buying your new television on the internet. Leading brands often offer superior service compared to unknown foreign manufacturers, so the price and image quality are the only factors to think about.