in early human history, darkness was very frightening. Wild animals and our enemies could kill us more easily in the darkness. We hid in our caves and waited for the light. The idea of light, or fire, cutting through the darkness, is a common one in various cultures and religions. We eventually learned to light fires to illuminate our caves or campgrounds at night, but as we started venturing out on the seas in boats, the idea of being out in the darkness was scary.

The first navigators traveled mainly during the day. As mariners ventured out more at night, some learned to plot their course by the movement of the stars and constellations. But there was always the danger of running into hidden rocks, shoals, and other obstacles.

The origins of the lighthouse go back to simple bonfires built on beaches and hillsides in many cultures around the world. The Greeks built braziers filled with fire and put them on hillsides at the entrances to harbors and along navigation routes to guide mariners. The Greeks also built some of the earliest true lighthouses at least as early as the fifth century B.C.—basically columns surmounted by fires.The world’s first great lighthouse, the Pharos of Alexandria, was built in the third century BC in the harbor at Alexandria, Egypt, a city that had been founded by Alexander the Great. It was built of giant blocks of limestone and had a furnace at the top, with the fire possibly magnified by a mirror. It stood more than 300 feet tall and is regarded as one of the seven wonders of the ancient world.acquired from http://light2015blog.org/2015/08/04/what-is-it-about-lighthouses/

                                                                   Seven Wonders of the World - Lighthouse of Alexandria

The struggle of nature vs. humans and their creations is at the heart of many of the most popular stories of lighthouses. There’s often great heroism in the struggle against nature.

Even in these days of GPS and other modern technology, lighthouses still serve a vital purpose for navigation. Electronics can fail, and when that happens there’s nothing better than the sight of a lighthouse to show us the way to safe harbor.

Lighthouses represent many things to many people, but they have universal qualities that make them a very special class of structure and help to explain why they’re so iconic in our culture. Lighthouses were built for completely positive, altruistic reasons–to safeguard life and property

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                                           Augustin Fresnel,
The headlights have evolved light mode used. Thus, coal replaced wood, oil lamps and coal electricity oil lamp. But even if these light sources were becoming more intense and less difficult to maintain, we needed a technology capable of increasing the scope of the emitted light beam. To this end, we put the oil lamp in the center of a parabolic reflector metal. This technique increased only very few reach the beam because the metal that was used to reflect the absorbed much of the energy emitted by the lamp. So we had the bright idea to wait a French polytechnic to see the performance of the headlights to improve considerably.
4.5 million times more intense
In 1821, Augustin Fresnel, an engineer at the Lighthouse Commissioners, proposed replacing the metal reflectors with wide lenses. These lenses, Fresnel say, consisting of a central disc convex (outwardly curved) surrounded by a series of concentric rings acting as prisms, focus the rays from a light source on a single plane. Indeed, at the exit of the lens, the light rays refracted by the concentric rings are parallel to each other and propagate along a single direction. This process allows the horizon to illuminate only avoiding ray scattering throughout space and increase to 4.5 million times the intensity of the light beam! It is so powerful that all the team gradually leading the world and is still the source of many light beams that sweep across our sky.
A language for sailors
The lighthouses indicate reefs or hazardous areas of the coast. But ligthouses not only to illuminate the first ribs. They also allow sailors to identify. Each lighthouse has its own characteristics, its own way to him to enlighten the horizon. Some lighthouses lights emit sectors, ie light beams of different colors: red or green to indicate dangerous areas, white to indicate the way forward. Those who send only white light, can be fixed lights (light intensity constant and identical in all directions), strobe lights (dark periods longer than the periods of light), lights isophases (time of darkness and light are identical), or lights dimming (light periods longer than the periods of darkness). To identify, then there remains only the sailor determine what type of fire light it up, count the times of darkness and light and measure the rate at which these periods are repeated. Referring to his list of lights, where all codes are shown headlights, he will discover the name of the lighthouse that illuminates and deduce its position relative to the coast. Useful if the GPS or radar failure.
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                                           the Fresnel lens
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                             On a bundle of rays through the Fresnel lens
                       The last lighthouse keeper from Netherlands