Television is a telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term has come to refer to all the aspects of television from the television set to the programming and transmission
The elements of a simple television system are:
An image source - this may be a camera for live pick-up of images or a flying spot scanner for transmission of films
A sound source
A transmitter, which modulates one or more television signals with both picture and sound information for transmission.
A receiver (television) which recovers the picture and sound signals from the television broadcast.
A display device, which turns the electrical signals into visible light.
A sound device, which turns electrical signals into sound waves to go along with the picture.
Display technology
Thanks to advances in display technology, there are now several kinds of video displays used in modern TV sets:
CRT: The most common displays are direct-view CRTs for up to 40 in (100 cm) (in 4:3) and 46 in (115 cm) (in 16:9) diagonally. These are still the least expensive, and are a refined technology that can still provide the best overall picture quality. As they do not have a fixed native resolution, in some cases they are also capable of displaying sources with a variety of different resolutions at the best possible image quality. The frame rate or refresh rate of a typical NTSC format CRT TV is 60 Hz, and for the PAL format, it is 50 Hz. 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, or VBI, allows other signals to be carried along with the broadcast.
Cutaway rendering of a color CRT
Electron guns
Electron beams
Focusing coils
Deflection coils
Anode connection
Mask for separating beams for red, green, and blue part of displayed image
Phosphor layer with red, green, and blue zones
Close-up of the phosphor-coated inner side of the screen
Rear projection: Most very large screen TVs (up to over 100 inch (254 cm)) 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.
Flat 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 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.
Buying Tips & Suggestions
If you are shopping for a new television, there are many things to consider before buying. Viewing habits, size of unit, size of screen, price, brand, style, type, and quality are all important issues. Don't forget to find out about the cost and time required for delivery if you are unable to retrieve the TV yourself.
When it comes to size, you need to determine not only the size of the room in which the TV will be placed, but also the size of the stand, entertainment center, or other unit that will house the television. Don't forget to bring a tape measure with you to the store so you can measure the TV you want to buy and make sure it will fit inside the unit. You need a little extra space around the television to allow airflow, to clean the TV, and to hook up other components.
When it comes to getting your new TV home, make sure the one you chose will fit inside your vehicle. Also, ask for help placing the television into your vehicle instead of struggling to maneuver it yourself. Make sure you have help available to bring the set in from your car once you arrive at home as well. Some shops offer free delivery if you spend a certain amount or buy a certain size TV or larger. In this case, you should take advantage of delivery, not only because it is more convenient, but also because the seller bears all the responsibility for the set until it is safely placed inside your home.
When choosing a TV, pay special attention to picture quality. The darker the screen when the set is turned off, the crisper the picture will be, because the TV can provide greater contrast than those with lighter screens, such as those that appear light gray or green. Also important is the curvature of the picture tube. Flat screens are preferred, because images are viewed in clean lines rather than curved lines, and there is far less glare from other light sources with a flat screen TV.
Technology 
