As an island nation, we in the UK are used to seeing lighthouses around our coasts, but have you ever stopped to contemplate when they were first built and the way they worked in those early days.
The aim of lighthouses is clearly to mark dangerous coastlines, rocks and reefs and to assist navigation, especially at night or in misty conditions.
The first known warnings made to boats of hazardous rocks and shores, were fires, set at the edge of the water, however it was in Egypt that we first heard of actual structures being built, which used light to guide ships.
The Lighthouse of Alexandria
Built on the island of Pharos, the lighthouse was commissioned by Ptolemy in 290 B.C. It took 20 years to build, and became the tallest building in existence, except for the nice Pyramid, standing at between 450 and 600 feet in height, and was recognised as one of the Seven Wonders of the World.
It’s thought to have cost around the equivalent of three million dollars or £2.8 million. Its design was nothing just like the slim structures we’re aware of today. It consisted of three stages, the first being in the shape of a large box built on a 20 foot high stone platform. On top of this was an eight sided tower, followed by a cylinder that extended to an open cupola where the fire burned to supply the sunshine. On its roof was a big statue, thought to be of the sea god Poseidon. The fire’s light was believed to have been projected right into a beam by way of a large curved mirror, probably manufactured from polished bronze. It was said that ships could detect its signals as much as 100 miles away, the light from the tower by night, and the smoke from the fire by day. This claim however seems just a little excessive.
The lighthouse became so famous that the name “pharosbecame the root of the word “lighthousein many languages. It stood for over 1,500 years, surviving a tsunami in 365 AD, but earth tremors resulted in cracks forming in the structure which needed restoration. Then, a major earthquake within the region, in the 14th century, caused such severe damage that the structure eventually collapsed.
Other early lighthouses
In medieval times the Iranians apparently erected large minaret towers in the mouth of the Persian Gulf to help navigation. In China, the medieval mosque at Canton also had a minaret serving as a lighthouse, and in 1165 a pagoda known because the Liuhe Pagoda, was in-built Hangzhou and acted as a lighthouse for sailors within the Qiantang River.
One of many oldest working lighthouses in Europe is Hook Lighthouse, constructed at Hook Head in County Wexford, Ireland in 13th century and in-built circular design. Two lighthouses, called the Pharos, were built at Dover (UK) soon after the Roman conquest of Britain. They were constructed on two heights (the Eastern and the Western). The one on the Eastern Height still stands in the grounds of Dover Castle.
Another famous early Roman lighthouse is the Tower of Hercules, probably inbuilt the primary century, on a peninsula at A Coruna in north-west Spain. It was originally known as the “Farum Brigantium the Latin word farum being derived from the Greek pharos.
The sunshine was originally produced using a wood fired system located on the summit platform, but the lighthouse was abandoned after the Viking Invasions of 854-56. It was restored within the 14th century when the town became one of the kingdom’s largest ports, and by the 17th century it had been fitted with a dome shaped lantern. More restoration was completed in the early 18th century, and in 1847, a system using Fresnel lenses (see later) was installed. It was electrified in 1926, with a beam visible for as much as 32 nautical miles and is the oldest Roman lighthouse in use today.
Some early lighthouses used wick lamps as a light source and sometimes the beam could only travel a few miles. The Argand hollow wick lamp and parabolic reflector were developed in Europe around 1781, while within the USA, whale oil was used with wicks until the Argand system was introduced around 1810,which was then later replaced with Colza oil (similar to rapeseed oil), lard oil after which Kerosene.
The Fresnel lens
In 1822 a Frenchman, named Augustin Fresnel, discovered how to extend the sunshine intensity using prisms, and the first Fresnel lens was installed in 1822 in the Cordouan lighthouse within the mouth of the Gironde estuary. This light could possibly be seen from 20 miles or 32 km away. By the 1860s, low-light-loss Fresnel lenses, much larger than the unique ones, were in use in lighthouses around Britain and France, their use quickly extending to Italy and further afield to Australia and America.
To create the flashing effect, designers needed to give you a way of constructing the lens revolve. This was done using a rotating stand with a clockwork mechanism with descending weights on cables. The keeper periodically cranked up the burden to the top of the lighthouse and as it descended, the lens revolved. The flashing effect was achieved each time a segment of the rotating lens passed between the lamp and the observer. The speed of rotation determined the frequency of the flash and made it possible for each lighthouse to have its own recognisable pattern.
The appearance of electricity
Across the turn of the 20th century, acetylene gas (electricity and carbide) began replacing kerosene, and around 1910 many lighthouses began using the clever device called the Dalen Sun Valve, invented by the Swede, Gustav Dalen. The valve opened and closed the gas supply to the lamp in accordance with how much sunlight it received, so the lights might be turned on automatically at dusk and off at dawn. Dalen also found out the way to store the gas in tanks and to interrupt its flow, causing the sunshine to flash. Dalen’s inventions resulted in savings in fuel and maintenance, as the lamps only needed servicing twice a year.
As electricity became available, the clockwork mechanisms within the lighthouses were replaced by electric motors, with 100W bulbs providing the sunshine source, and electronically operated fog signals were added. With all this electrification and automation, lighthouse keepers were sadly obsolete and from the 1980 they became superfluous to requirements. The last lighthouse in the UK to be automated was North Foreland in Kent, in 1998.
Many Fresnel lenses have been replaced by rotating aerodrome beacons which require less maintenance. The system of rotating lenses has in some cases been replaced by a high intensity light that emits short flashes, much like the obstruction lights used to warn aircraft of tall buildings.
Recent innovations include Vega Lights, (lighthouse beacons providing a range of as much as 22 nautical miles with a 100 Watt lamp). They will operate in remote, solar-powered locations, on unattended sites, and require maintenance only once a year. There are within the region of 600 of those in operation around the world.
Technology moves on, and as new innovations equivalent to GPS make navigation easier and safer, it could also be tempting to think that lighthouses have had their day.
Personally I’d prefer to have a reliable backup to my GPS, and there’s nothing so comforting in your first ever night watch under sail, than to see the beam of a lighthouse shining through the darkness, to count the flashes and know that you’re where you ought to be.
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