Lighthouse Technology

Light has been used to guide ships for over 3000 years. The earliest lights were signal fires lit on headlands. Later the fires were maintained on a grate or an iron basket (brazier) on a high location such as a masonry tower or platform. The earliest known lighthouse was the Pharos of Alexandria, which was built around 285 BCE to a staggering height of 130 meters (426 feet). The Pharos was in use for almost 1600 years until it was destroyed by an earthquake in 1302 CE.

The problem with signal fires was that less than 1% of the light could be seen by mariners. There was some improvement when coal was used instead of wood in the braziers in some countries.

A further improvement was the use of a lantern with a flue to get rid of smoke which sometimes obscured the light. The lantern was useful when candles came into use as it kept out much of the wind.

By the 19th century enclosed wick lamps became popular. They burned a variety of oils which produced a brighter light than candles. Some of the oils used were whale, seal, fish, rapeseed and even oil from sheeps’ tails.

In 1846, Dr. Abraham Gesner of Nova Scotia discovered a process whereby kerosene could be produced from coal. It was a discovery that would revolutionize light keeping through out the world.

Lamps with one oil source and a number of wicks increased the intensity of the light. The use of polished metal reflectors began in the mid 1600’s. The spherical and parabolic mirrors, with their curved or egg-shaped interiors, gather and intensify the weak flame produced by the oil lamp wick and project it forward. The reflecting system was called the “catoptrical” system. A reflector-equipped light is on display at the West Point Lighthouse Museum.

Francois Pierre Aime Argand developed a system of concentric wicks in 1782, which became known as the Argand oil lamp. He also invented the use of a chimney to provide additional air flow over the wick and protect the flame from drafts. This increased the brightness of the flame.

Robert Stevenson improved Argand’s lamp in the early 19th century with a design that made it easier to replace the wicks and polish the reflectors. This version was widely used, either singly or in a grouping like at Cape Bonavista Lighthouse in Newfoundland.

The simple catoptrical systems used mirrored reflectors. Augustin Fresnel invented the dioptric lens system which employs only the reflective property of glass to make the equivalent of a large lens with concentric rings of small prisms. He also created a catadioptric system which uses both reflection and refraction. The Fresnel lens is like a bulls-eye surrounded by a number of concentric rings of glass. Barbier, Renard and Turenne of France and the Chance Brothers in England produced most of the Fresnal lenses in use today. The Fresnel lenses range from very small to the enormous hyper radials like the one at Cape Race, Newfoundland.

Lighthouses were identified by their light. There were three main types: fixed, flashing and interrupted. A fixed light appears continuous and steady and of constant colour. A flashing light is one in which the total duration of light in each period is clearly shorter than the total duration of darkness and in which the flashes of light are all of equal duration. Interrupted quick flashing light is one in which the rapid alternations are interrupted at regular intervals by eclipses of long duration. Thus each light can be identified by its own flash pattern at night and by its unique painted day marks during the day.

To create the flashing pattern, mirrors or lenses could be rotated around a central stationary light. The lights were rotated by a clock and gear mechanism. Weights ran through a square wooden shaft. The keeper had to wind the weights from the bottom of the weight shaft every two to four hours.

In many cases the light itself rotated on a mercury float. The light system was supported on a circular cast iron vessel that floated in a bath of mercury, which allowed the lights to turn easily. Today mercury has been removed from all Island lighthouses due to its toxic nature.

Improvements were also made to the lights themselves with the development of mantles lit by hot vapour in the same manner as many camp stoves operate today. This provided a brighter flame and used less fuel.

When the lighthouses were electrified most of the keepers were retired or transferred. Powerful electric bulbs were installed. Some of the lighthouses were equipped with lamp changers in case of a burnout. If one bulb burned out, the mechanism automatically rotated to the next bulb.

Prince Edward Island lighthouses had been illuminated by vapour mantle lights or 500 watt electric light bulbs until 1961. At that time, new 400 watt mercury vapour lights were installed on a testing basis at four Canadian lighthouses, including Souris East Lighthouse. The keeper there, Donald Osborne, reported a “very bright light.” The test was equally successful elsewhere and mercury vapour lights are standard today.

With the advent of scientific navigational equipment such as Loran C and Global Positioning Systems (GPS), mariners are no longer as dependent on lighthouses for guidance as they once were. The older lights have been replaced in many lighthouses throughout the world. On Prince Edward Island, for example, the 4th order lens at East Point Lighthouse has been replaced with a beacon of less intensity which mainly serves the local fishing boats and other near-shore traffic.

Acetylene was invented by a Canadian, Thomas Leopold Wilson, in 1892. Gustav Dalen of Sweden invented an acetylene regulator flasher lamp for use in lighthouses or buoys. He also developed a sun flasher which automatically turned off the light during the day to save fuel. On PEI such flashers were often used on buoys. Today many buoys are powered by solar panels.

The first fog alarms were hand operated. Examples can be seen at Point Prim and East Point Lighthouse. A large fog alarm building was constructed at East Point Lighthouse in 1908 to house a steam and compressed air diaphone. Keepers and assistants worked hard to maintain the coal fires and the machinery. Various other types of fog alarms were used over the years. A Stone-Chance electric fog horn was installed at East Point Lighthouse in 1971. A balcony was added to the tower to assist in maintenance of the fog alarm. All fog alarms were removed from Prince Edward Island in the late 1990’s.