How an LCD TV works

An LCD TV is sometimes referred to as a "transmissive" display. Light isn't created by the liquid crystals themselves; instead, a light source behind the LCD panel shines through the display. A diffusion panel behind the LCD redirects and scatters the light evenly to ensure a uniform image.

The display consists of two polarizing transparent panels and a liquid crystal solution sandwiched in between. The screen's front layer of glass is etched on the inside surface in a grid pattern to form a template for the layer of liquid crystals. Liquid crystals are rod-shaped molecules that twist when an electric current is applied to them. Each crystal acts like a shutter, either allowing light to pass through or blocking the light. The pattern of transparent and dark crystals forms the image.

The multi-layered structure of a typical LCD panel. Because they use red, green and blue color filters in place of phosphor dots, LCD TVs are completely immune to screen burn-in.

LCD TVs use the most advanced type of LCD, known as an "active-matrix" LCD. This design is based on thin film transistors (TFT) — basically, tiny switching transistors and capacitors that are arranged in a matrix on a glass substrate. Their job is to rapidly switch the LCD's pixels on and off. In an HDTV's LCD, each color pixel is created by three sub-pixels with red, green and blue color filters.

An important difference between plasma and LCD technology is that an LCD screen doesn't have a coating of phosphor dots (colors are created through the use of filters). That means you'll never have to worry about screen burn-in, which is great news, especially for anyone planning to connect a PC or video game system.

How a plasma TV works

A plasma TV is sometimes called an "emissive" display — the panel is actually self-lighting. The display consists of two transparent glass panels with a thin layer of pixels sandwiched in between. Each pixel is composed of three gas-filled cells or sub-pixels (one each for red, green and blue). A grid of tiny electrodes applies an electric current to the individual cells, causing the gas (a mix of neon and xenon) in the cells to ionize. This ionized gas (plasma) emits high-frequency UV rays, which stimulate the cells' phosphors, causing them to glow the desired color.

Each individual plasma cell is switched on and off by its own electrode. A plasma HDTV can have up to 6 million cells.

Because a plasma panel is illuminated at the sub-pixel level, light output is very consistent across the entire screen area. Plasmas produce the widest horizontal and vertical viewing angles available — pictures look crisp and bright from virtually anywhere in the room.

Because plasma TV screens use a phosphor coating like CRT-based TVs, the possibility of screen burn-in exists, though it's unlikely to happen with current models. To reduce the chance of burn-in, be sure to follow the manufacturer's recommendations on setup and use.