TV Technologies

TV's basically come in six different flavours – Plasma, LCD, LED, OLED, CRT, and Rear Projection. While the differing technologies may sound complex, they don't need to be.

Plasma
Capsules of xenon, neon, or argon gas sandwiched between two planes of glass are chemically excited by an electrical current. When excited enough, the gas changes to a plasma, releasing light. The light strikes a phosphorescent layer which produces the required coloured light in each pixel making up the image.

The key features of plasma's are:

• They're economical to manufacture in large sizes, so really big TV's tend to be plasmas
• The have a bright image relative to other TV technologies
• Fast moving images don't blur (unlike on LCD and LED TV's)
• Their glass screens make them prone to picking up reflections in brightly lit rooms
• They are not very efficient – consuming relatively large amounts of electricity
• They are prone to image burn-in

LCD

White light from a series of cold cathode fluorescent lamps (CCFL's) at the back of the TV panel is blocked or allowed through LCD shutters (liquid crystal display – basically the same technology you find on a digital watch face) into red, blue, or green filtered sub-pixels. Switching the light on or off into the sub-pixels creates the appropriate coloured light in each pixel making up the image.

The key features of LCD's are:

• Reduced electricity consumption compared to Plasma TV's
• They are immune to image burn–in
• While the gap is closing, they tend to be expensive in the largest sizes
• LCD's struggle with fast moving images (e.g. sports) causing blurring
• Their viewing angle generally isn't as good as Plasma TV's

LED

This is a marketing term for a type of LCD TV that uses LED's (light emitting diodes) to supply the white light coming from the back of the TV panel. Despite some recent hype about this being a breakthrough technology, it's been around on some TV's since 2004. LED TV's come in two flavours, edge lit (where the LED's are arranged around the outer rim of the TV panel facing inwards) or back-lit (where the rear of the TV panel is made up of LED's).

The key features of LED's are:

• Reduced electricity consumption compared to CCFL LCD and Plasma TV's
• Edge lit TV's tend to be extremely thin and lightweight
• Depending on the technology used (more about that here) LED TV's may display better contrast ratio's (i.e. a deeper blacks) than CCFL LCD TV's
• They are more expensive to produce than CCFL LCD TV's

OLED

Unlike so called LED TV's, OLED TV's are based on a 'true' LED TV technology. Each pixel on the screen is made up of either a red blue or green organic light emitting diode ('organic' is chemistry speak for saying a material contains carbon), which when stimulated by electricity the pixel fluoresce, producing coloured light. The key difference between is that unlike LCD and LED technology, OLED TV's require no backlight, making them extremely energy efficient.

The key features of OLED's are:

• Being made up of just a single layer the panel can be extremely thin, just a few millimetres in some cases
• The most energy efficient of all the TV technologies
• A very new technology that is only available in a few products
• Very expensive to produce, in the short term you are more likely to see these used in laptop displays rather than TV's.

CRT

This is the old-fashioned tube TV that's been around for sixty years or more. A beam of electrons is steered to hit a phosphorescent layer at the front of the screen, forming an image.

The key features of CRT's are:

• Though you can't buy one new, second-hand models are very cheap
• Heavy, and relatively energy inefficient
• A dated technology that is no longer manufactured

Rear Projection

These project a video image from a LCD, CRT, or DLP projector at the rear of the cabinet onto the screen using a system of mirrors

The key features of rear projection TV's are:

• Cheap to produce for large screen sizes
• The arrangement of mirrors means that the TV cabinet can be shallower than CRT TV's – though still much deeper than flat panel plasma, LCD, LED, and OLED TV's
• Rear projection TV's lack brightness, and can look washed out in well lit rooms
• A dated technology that is rapidly dying out