Television (idea)

An Aerial
A Tuner
A Visual Decoder
An Audio Decoder
A Visual Amplifier
An Audio Amplifier
A TV Tube
Three Electron Guns

When carrier waves (amplitude modulated waves used to carry signals) are picked up by the aerial as high-frequency radio waves, it is carried to the tuner, which picks out the desired frequency selected by the viewer. The visual signal is then separated from the carrier wave in the visual decoder, and the audio signal is separated from its carrier wave by the audio decoder. Both signals are then carried to the visual and sound amplifiers respectively. Here, the signals amplitude is increased in order to strengthen it. The signals are then carried to the TV Tube.

A television screen is coated with a special type of paint which glows when hit with electrons, fired in a stream from an electron gun. A picture is built up by line buildup - the electron gun is moved across, up and down the screen rapidly at a speed of approximately 24000 km/h. On a standard British television, a screen is made up of 625 lines. By varying the number of electrons in the beam, the brightness of the picture can be varied. This is known as brightness variation. Twenty-five images are produced per second, meaning there is a gap of one twenty-fifth of a second between pictures. However, the human eye retains an image for a fraction of a second after it has disappeared (known as image retention or persistence of vision), meaning that the pictures overlap and it is seen as a moving image.

In order to create coloured pictures, the screen must be dotted with three different colours of paint: red, blue and green (the primary colours of light, different from the primary colours of art). Three electron guns are used instead of one, and each is designed only to hit a certain colour. Other colours are produced by mixing the colours together and varying the intensities of the electron beam. For example, magenta can be made by combining the red and blue pixels, and cyan can be made by mixing the blue and green. When all three colours are illuminated, white is displayed and when there is no light, we see black.

Plasma televisions display images using a different method. Voltage is applied to transparent electrodes within the screen, causing them to discharge into noble gases such as neon or xenon, which creates plasma. Electricity is briefly conducted by the plasma and a burst of ultraviolet rays is emitted, stimulating phosphors which emit red, green or blue light. By reversing the polarity, the cell can be cleared of any charge and prepared for the next cycle. Every set of adjacent red, blue and green chambers consist of pixel, meaning that a screen could have up to a million of them. There are several drawbacks to plasma televisions, aside from the price (the cheapest being $5,000). For example, according to experts, if a static image is displayed for long enough on the screen, it would be burned in permanently in the same manner as older computer monitors.

An LCD (liquid crystal display) screen displays an image by way of a back light shining through a matrix of pixels, each filled with liquid crystals. Voltage is applied to each pixel using a film-thin transistor, causing the crystals to align to different degrees, allowing different amounts of red, green and blue light to be displayed. LCD screens can easily be told apart from plasma in that when viewed from extreme angles, the colours of the picture distort and become inverted.

Many believe the future of television to lie in Organic Light Emitting Diodes, thin polymer films which create an image when they glow. Although the largest screen yet created measures only a few centimeters wide, they can be found on mobile phones and other electronic devices. They can be bent like plastic, being only an eighth of an inch thick. Organic Light Emitting Diodes consist of anode metal, organic polymer and cathode metal deposited on flexible glass, which forms a pixel. When current is applied to the anode and cathode, electrons and holes are sent into the polymer, where they collide, causing the polymer to glow red, green and blue.