The screen in liquid crystal display TVs typically has two sheets of polarizing material with the liquid crystals squeezed between them. To create a television, a current passes through the crystals, controlling which ones let light through. Some LCD televisions use fluorescent light, but LED sets use light-emitting diodes instead. LCD TVs can't go completely black, and don't catch all the details of fast motion on screen. It's the most common TV technology, though, so you have a wide range of options when you go shopping.
Plasma screens use tiny gas cells to illuminate the pixels in an image. Plasma technology renders fast motion smoothly, and offer deeper contrasts than LCD sets. You can also watch at a wider angle than an LCD television without losing picture quality. Plasma sets are, however, heavier and thicker than LCD sets. As of 2014, only a couple of manufacturers make them, so your choice of models is limited.
OLED televisions use organic light-emitting diodes to illuminate each picture element individually, rather than backlighting the screen. This creates a more colorful, brighter picture than any competing technology available at time of writing. Like most new tech, it's expensive: a 55-inch set runs $9,000. It's also possible that some images may "burn in," staying on the screen instead of fading.
Ultra high-definition sets, also known as "4K," don't offer a new technology. What they do offer is many more pixels on the screen, giving them up to four times the resolution of a regular high-definition TV. However, nobody at time of writing is broadcasting in UHD, and the superior resolution isn't as noticeable with a regular HD broadcast image.
Three-dimensional TV works under the same technology as 3D movies. The TV displays two separate images simultaneously; you put on glasses which merge the image into one combined picture. There are no purely 3D sets, but high-end 2D televisions have offered 3D as an option since 2010. The glasses come with the TV. There aren't a lot of 3D viewing options, though; Blu-ray DVDs in 3D are currently the primary source of material.