Lighthouses: FAQ
Source: The United States
Coast Guard
Our first lighthouses were actually given to us by
Nature. Sailors sometimes used landmarks such as glowing volcanoes to guide them. In the Ancient World, trading ships were
eventually built enabling navigators to sail long distances to buy and sell goods. In the days of wooden ships with sails,
the wind and waves could easily push them against the rocks and wreck them. And so, the need for lighthouses as warning signals
arose.
One of the Seven Wonders of the Ancient World was a
lighthouse—the famous Pharos of Alexandria, Egypt. It is the first one that is recorded in history and was built about
280 BC. Those records tell us that it was the tallest one ever built—450 ft. (comparable to a 45-story skyscraper) and
used an open fire at the top as a source of light. This fantastic structure survived for 1500 years until it was completely
destroyed by an earthquake in the 14th century.
Today we call people who study (or are interested in)
lighthouses pharologists. The name comes from that famous lighthouse.
What is a lighthouse?
It is a tower with a bright light at the top, located
at an important or dangerous place regarding navigation (travel over water). The two main purposes of a lighthouse are to
serve as a navigational aid and to warn boats of dangerous areas. It is like a traffic sign on the sea.
When the lighthouses were built, they were constructed with whatever materials were
most readily available. They were designed to fit the local geographic and climatic conditions. Some are made of stone; others
brick, concrete, wood, steel, cast iron, and even tabby (a mixture of shells, lime, sand and water).
Where are lighthouses located?
The United States has several coastlines used by ships
from around the world. In the East it borders the Atlantic Ocean, in the West the Pacific Ocean, and in the South the Gulf
of Mexico. But we also have another very important area of coastline where the land meets the sea, the Great Lakes. All of
these four areas bordering our country need and have lighthouses, as well as some of our more important navigable inland waterways.
For example, the Hudson River, Lake Champlain, Chesapeake Bay and San Francisco Bay are also dotted with lighthouses.
How could one lighthouse be distinguished from another?
Years ago, to help the sailor determine his location,
the Lighthouse Board (which was in charge of lighthouses from 1852–1910) issued an order to have each lighthouse painted
in different colors and/or designs.
But what about night? You can't see colors or patterns
at night, but you can see lights. However, unless there was some way to make each light different you could have the same
problem. Early on, they built multiple lights (that is, two or three together.) This was one way to help the sailors at sea
determine their location, but it was very expensive.
Mounting a group of lights on a rotating framework
made it possible to produce a special pattern of light for each lighthouse. The rotating lights made a lighthouse look like
it was flashing its light on and off. The invention of the Fresnel (pronounced “Frey Nel”) lens in 1822 was probably
the most important discovery in lighting technology. As well as enabling man to produce an unlimited number of flashing combinations,
it also intensified (brightened) the light so it could be seen at greater distances.
The Fresnel lens can be compared to a huge lampshade
except that it is made of 100s of pieces of beautiful, specially cut glass. It surrounds the lamp bulb. This lens, due to
its special design, brightens the glow from the light. It takes the rays of light, which normally scatter in all directions,
and bends (refracts and reflects) them, focusing them into a single beam of light. Fresnel lenses are of two types: fixed,
which shows a steady light; and revolving, which produces a flash.
