Each light gives out flashes of different timing and length so that sailors can tell which light they are seeing many kilometres away - just by timing the light and looking it up in a guide book. But there are some major problems with using light this way to send messages. This is partly because the Earth is curved, and partly because as light radiates out from a source it gradually becomes weaker because of the effects of dust and smoke in the air and because of the inverse square law of radiation . Pushing light through a pipe A cleverer way of using light to send messages is to push it through a pipe much in the same way as water is moved around through pipes. This is where 'light pipes' better know as optical fibres come in.
Optical fibres are long strands of transparent material which let the light pass through the middle.
So the light travels along the fibre bouncing off the mirror-like outer casing until it arrives at the other end of the fibre. These optical fibres - which are thinner than a human hair work when bent around corners, laid underground or even laid on the ocean floor. And because the light is contained within the walls of the fibre and can't disperse or radiate away, it takes very little light energy to send a signal over a long distance. Also, as light travels at about 300,000 kilometres per second, you could use your torch to flash a signal right around the world in next to no time. Of course, actually doing it is much more complicated than that, but that is the principle on which it works.