Television

Television (often abbreviated to TV, T.V.; sometimes called the tube, or telly in the UK) is a widely used telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term may also be used to refer specifically to a television set, programming or television transmission. The word is derived from mixed Latin and Greek roots, meaning "far sight": Greek τῆλε "tele", far, and Latin vision, sight (from video, vis- to see).

Since it first became commercially available from the late 1930s, the television set has become a common household communications device in homes and institutions, particularly in the first world, as a source of entertainment and news. Since the 1970s, video recordings on VCR tapes and later, digital playback systems such as DVDs, have enabled the television to be used to view recorded movies and other programs.

A television system may be made up of multiple components, so a screen which lacks an internal tuner to receive the broadcast signals is called a monitor rather than a television. A television may be built to receive different broadcast or video formats, such as high-definition television (HDTV).

The elements of a simple television system are:

An image source - this may be a camera for live pick-up of images or VTR or a Film Chain-Telecine-flying spot scanner for transmission of films.
A sound source picked up by a microphone
A transmitter, which modulates one or more television signals with both picture and sound information for transmission.
A receiver (also called a tuner) which recovers and processes the picture and sound signals from the television broadcast signal.
A display device, which turns the electrical signals into visible light and images
A small amplifier and loudspeaker, which turns electrical signals into sound waves (speech, music, and other sounds) to accompany the images.
Practical television systems include equipment for selecting different image sources, mixing images from several sources at once, insertion of pre-recorded video signals, synchronizing signals from many sources, and direct image generation by computer for such purposes as station identification.

Transmission was originally over the air from land-based transmitters. The quality of reception varies greatly, and this led to the proliferation of large antennas on house roofs for best signal in the 1960s. In most cities today, cable systems deliver television over metal or optical cables, but for a fee. It can be delivered by radio from synchronous satellites, which were large for analog, and smaller dishes for digital broadcast, also for a fee, often less than cable systems, which has led to the appearance of small dishes outside of houses and apartments.

Digital systems may be inserted anywhere in the chain to provide better image transmission quality, reduction in transmission bandwidth, special effects, or security of transmission from reception by non-subscribers. A home today might have the choice of receiving analog or HDTV over the air, analog or digital cable with HDTV from a cable television company over coaxial cable, or even from the phone company over fiber optic lines. On the road, television can be received by pocket sized televisions, recorded on tape or digital media players, or played back on wireless phones over a high speed network or the internet.

Thanks to the advances in display technology, there are now several kinds of video displays used in modern TV sets:

CRT (cathode-ray tube): The most common screens were direct-view CRTs for up to roughly 100 cm (40 inch) (in 4:3 ratio) and 115 cm (45 inch) ((in 16:9 ratio) diagonals. These are the least expensive, and are a refined technology that can still provide the best overall picture quality value. As they do not have a fixed native resolution, they are capable of displaying sources with different resolutions at the best possible image quality. The frame rate or refresh rate of a typical NTSC format CRT TV is 29.97 Hz, and for the PAL format, 25 Hz, both are scanned with two fields per frame in an interlaced fashion. A typical NTSC broadcast signal's visible portion has an equivalent resolution of about 640x480 pixels. It actually could be slightly higher than that, but the vertical blanking interval (VBI), allows other signals to be carried along with the broadcast.
Rear projection (RPTV): Most very large screen TVs (to 100 inches [254 cm] or more) use projection technology. Three types of projection systems are used in projection TVs: CRT-based, LCD-based, and DLP (reflective micromirror chip) -based. Projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of the CRT; current models are vastly improved, and offer a cost-effective large-screen display.
A variation is a video projector, using similar technology, which projects onto a screen.

A modern Philips LCD TVFlat panel (LCD or plasma): Modern advances have brought flat panels to TV that use active matrix LCD or plasma display technology. Flat panel LCDs and plasma displays are as little as 25.4 mm (1 inch) thick and can be hung on a wall like a picture or put over a pedestal. Some models can also be used as computer monitors.
LED technology has become one of the choices for outdoor video and stadium uses, since the advent of bright LEDs and driver circuits. LEDs enable scalable ultra-large flat panel video displays that other technologies may never be able to match in performance.
Each has its pros and cons. Flat panel LCD and plasma displays have a wide viewing angle (around 160 degrees) so they may best suited for a home theatre with a wide seating arrangement. Rear projection screens do not perform well in daylight or well-lit rooms and so are only suited to darker viewing areas.