LED is an acronym for light-emitting diode, an electronic device that allows current to flow freely in one direction and emits light as it does so. In the case of an LED TV, LED simply describes the technology used to illuminate the screen. An LED TV is, in fact, a liquid crystal display (LCD) TV with LED backlights, rather than conventional cold cathode fluorescent lamp (CCFL) backlights.
LED Versus CCFL
LEDs can be arranged across the entire back of an LED TV display, known as "full-array,'' or just around the perimeter to create what is known as an "edge-lit" display. In either case, replacing bulky CCFL backlights with smaller LEDs means that LED TVs can be built even slimmer than conventional LCD TVs. LEDs are also more energy-efficient than fluorescent lamps, so LED TVs typically use less power than conventional LCD and plasma TVs, depending on the screen size and picture brightness.
One of the advantages of LED over conventional LCD is the ability to independently dim portions of the screen -- known as local dimming -- to create darker, more realistic blacks. This, in turn, improves the contrast ratio -- the ratio of the darkest and lightest shades that the screen can display simultaneously -- and makes the image as a whole appear crisper. It is worth remembering, however, that overall picture quality depends more on the processing software inside the TV than the technology employed to illuminate the screen.
On the downside, a full-array backlit LED TV with 1,080 horizontal scan lines, progressively scanned -- otherwise known as 1080p -- would require 2.1 million LEDs to illuminate 2.1 million individual picture elements, or "pixels," to perform perfect local dimming. This number of LEDs is prohibitively expensive, but engineers are trying to improve edge-lit LED display technology to the point where it rivals full-array LED backlighting.
The development of the first true, all LED TV screen is credited to J.P. Mitchell in 1977. Mitchell's black-and-white prototype, which was just 1/4-inch thick, was presented at the International Science and Engineering Fair in Washington, D.C., in May 1978 and received widespread recognition from the likes of NASA and General Motors. The initial design featured hundreds of LEDs and the then newly available transistor-transistor logic memory. Mitchell's scientific paper also proposed an LCD matrix design, which would ultimately replace traditional cathode ray tube technology and pave the way for modern flat-panel TV screens.
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