Childrens Illustrated Encyclopedia

television

519

1. Light source
   at back of screen
   (backlight) gives
   out white light.
   2. A special filter
   lets through only
   vertical beams of light.

NEW TECHNOLOGiEs

Today’s widescreen TV

sets have flat plasma

screens or liquid crystal

displays, but these will

be replaced by ultra-

thin organic LED

displays (OLED).

High-Definition

(HD) broadcasts

and screens use more

pixels to give better

picture quality. At home, personal

video recorders (PVRs, or VCRs)

store video on computer hard disk

drives. Movies and TV shows can now

be downloaded from the Internet,

too. Digital broadcasting uses binary

code to carry TV signals with better

quality sound and pictures. And with

interactive television, viewers can

select what to watch and when from

a wide range of options.

TELEVIsIOn RECEIVER

A television receiver picks up signals broadcast by television stations and converts

them to moving pictures on a screen. Images appear to move because 25-60 pictures

appear each second. The most common type of screen is the LCD (Liquid Crystal

Display). LCDs are made up of millions of tiny dots of light called pixels. Each pixel

contains a red, a green, and a blue subpixel—different combinations of these three

colors can produce all the colors that make up a picture. The subpixels are

controlled by groups of liquid crystals. Electronic circuits in the TV work out which

pixels need to be switched on to make a picture. They pass electric signals through

the liquid crystals, which act like tiny light switches to turn each subpixel on or off.

Find out more

Cameras

Electronics

Information technology

Radio

sound

TELEVIsIOn TRAnsMIssIOn

Television signals can reach a viewer by several

routes. Usually, transmitters broadcast television

signals directly to homes as ultra-high

frequency (UHF) radio waves. Alternatively,

the signals are sent up to a satellite, which

transmits them over a larger region.

Individual homes receive the satellite

broadcast via dish antennas

(right). In other cases,

a ground station picks

up the signals and

sends them out

along cables.

Satellite television

sends signals from

the TV station to

homes via a

satellite.

3. Electricity makes liquid
   crystals twist or untwist.
   Twisted crystals twist the
   light beams, too.

Cable

television

House aerial

picks up

UHF signals.

Television

station

VIDEO CAMERAs

Today’s video cameras,

or “camcorders,” are

tiny in comparison

with the giant studio

cameras used in the

early days of TV. They

fit easily in the palm of one

hand. Most are now digital

and record high-quality

video sequences—including

stereo sound as well—in the

form of binary code stored

on removable memory cards

iNvENTiON

In 1926, scottish engineer John Logie Baird

(1888-1946) gave the first public

demonstration of television. Later,

Russian-American engineer

Vladimir Zworykin (1889-1982)

invented the electronic camera

tube, which was followed by

other electronic tubes that

have now been replaced by

digital sensors. In 1956, the

Us company Ampex invented

videotape. Video cassette

recorders appeared in 1969,

produced by sony of Japan.

Pocket digital

music and

video player

High-definition

flatscreen television

Personal video recorder

4. Colored filters
   change the white
   light beams into red,
   green, or blue light.


5. Filter lets through
   only the beams of light that
   have been twisted horizontal
   by the liquid crystals.

No light reaches

the glass, so this

subpixel is dark.

6. The light from the
   switched-on subpixels
   reaches the glass screen
   and combines to form a pixel.
   7. Human eye
   sees different
   combinations of
   light beams as
   different colors.

How liquid crystals control

pixel colors in an LCD screen

The horn collects

concentrated

incoming waves.

Camcorder

Cable feeds the

signal into the house

to the receiver.

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