Technicalities and Selected Statistics

The Highest Lights

THIS TABLE SHOWS the twenty-five lights with focal planes 200 feet (about 60m) or more above the sea.

The Tallest Towers

THIS TABLE SHOWS the twenty-four towers 100 feet (30m) or more high.

The Brightest Lights

THERE ARE SIX LIGHTS around the Scottish coast, including, as lighthouse people must do, the Isle of Man, of a million candlepower or more. They are: St Abb's Head, Strathy Point, Swilkie Point and the Calf of Man (each one million); Buchan Ness and Mull of Galloway (each just over two million). Lights of comparable brightness in England and Wales are: The Lizard, Tynemouth North Pier, Bardsey and Strumble Head (each one million), and in Ireland: Baily and Rathlin East (one million), and Black Head, Tory Island and Aranmore (each about one and a half million). Buchan Ness and the Mull of Galloway are thus the brightest lights in the British Isles.

There are a number of lights as bright or brighter on the north coast of France. These are: Dunkirk, Ver-sur-mer and Cap de Carteret (one million); Ile Vierge (one and a half million -- this is also the tallest lighthouse structure known to Michael, 82 metres); Roches Douvres (two million); the leading lights at St Mathieu (two and three million); Cap Gris-Nez, Cap d'Antifer, Pointe de Barfleur and Cap Fréhel (three million); Pointe d'Ailly (almost seven million); Créac'h (nine million); and the leading lights at Port d'Antifer (both well over ten million). These intensities are taken from the Nominal Range table in Volume A.

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Tube-Lights

A TUBE-LIGHT IS Michael's unofficial name for a specialist light visible over a restricted sector, whose characteristic varies with the direction from which it is viewed. The characteristics are arranged to mark a leading line and to show unambiguously which side of that line the mariner currently stands. The limits of the visible sector are fixed by a long tube mounted in front of the lamp. These lights were originally used for marking submarine paths in the Firth of Clyde, but are becoming more common to mark leading lines and lights in line in all kinds of situation.

The directional light itself is an interesting device: a filter on a circular track rocks back and forth in front of the light source. One end of the filter is green, the other red, and there is a blank space in between through which the source appears white. If you stand at the extreme end of the cone of vision, you always see a red (or a green) light; in the middle, always white; and just outside the white sector, an alternating light with the coloured phase of shorter or longer duration depending on your angle of view. Thus the phase of the green light decreases, and that of the red light increases, with increasing bearing. Draw a picture and all will become clear.

There is a passenger ferry from Gourock across the river to Kilcreggan, and then across the mouth of the Gareloch to Helensburgh. You see these directional lights coming into view one after another, with the phase changing as you pass, and you see what submarines must see as they approach their base at the head of the loch. (See also the large-scale plan at Section J, Gareloch.)

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Sealed-Beam Units

THESE NOTES WERE TAKEN AT Ardnamurchan Lighthouse in June 2006. The lantern there consists of two banks of sealed-beam lamp units, one above the other, staggered by 45°. Focusing is entirely achieved by the reflectors in the sealed units: there are no external lenses or other optics at all. The beams are focused to be 9° wide, and the whole assemby rotates once every 20 sec. This gives the desired characteristic: flash 0.5 sec, eclipse 2 sec, flash 0.5 sec, eclipse 17 sec.

Each bank contains four sealed units in a horizontal row, each unit drawing 10 amps at 30 volts through a coiled tungsten filament (these are not halogen units as one might expect from car technology). Thus at full power the lantern consumes 2.4kW. At each end of the horizontal bank are two further, smaller, sealed units, which run on 6V at an unstated wattage. These come on when the light starts up and are replaced by the main units after a minute or so. The attendant on duty at the light could not explain why this is done.

An emergency unit stands on a pedestal inside the lanternhouse, close to the centre of the unobstructed arc of window. It contains a filament lamp that flashes the characteristic if the main units go down.

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Solar Power

THESE NOTES ARE TAKEN FROM the Notice to Mariners No. 1 of 2006. While Notices to Mariners are published for the use and information of anyone, copyright in their texts remains with the Commissioners of Northern Lights operating as the Northern Lighthouse Board.

"The refurbishment programme of the Northern Lighthouse Board (NLB) has been ongoing since 1998 and will be complete by 2004 for replacement of Acetylene and Propane gas systems with solar electric energy. Eight primary battery-powered lights will be solar-powered by 2005, giving a total of 120 solar-powered lights. Sixteen other diesel-powered sites will be progressively converted to solar-powered operation.

"The characteristics of the gas light will be emulated by the new electric lantern and will, where appropriate, include the retention of coloured sector arrangements. However, during the construction phase it is very often necessary to use temporary lights of lower range and without sector marking, due to power supply restrictions.

"NLB have operated gas-powered systems for more than 100 years and they were the first automatic lights in Scotland. In general they were installed where a low range, eg less than 10 miles, was required. A local attendant ensured that the gas supply was available and illuminated and that the gas mantle was in good condition. The structure or building (not a traditional lighthouse tower but a small brick building or cast iron cylinder) was regularly painted. An annual gas delivery by NLB tender was necessary. Today these structures can be replaced with low-maintenance aluminium towers and eco-friendly solar electric power for the electric lights. Such lights have been operated by NLB since 1985 and have been used in buoys since 1993. There are currently 126 NLB solar-powered land based sites from Holm of Skaw at the north tip of the Shetland Isles to Chicken Rock at the south end of Isle of Man, in addition to some 105 floating solar systems all around the coastline. The range of light varies between 3 miles and 23 miles. Lights of less than 15 miles are normally tungsten lamps exhibiting the advertised character by using electronically-controlled flashers switching the lamp on and off.

"NLB’s first automatic long-range lights were also powered by acetylene gas and were first installed in the early 1960s. Lens systems mounted on a turntable rotated using the gas pressure from the acetylene gas cylinders were installed in traditional lighthouse towers. A sun-sensitive gas valve controlled the supply to the gas mantle, allowing economic use of the available gas. Nevertheless, an annual supply trip by NLB tender was necessary.

"Development of high-efficiency metal-halide lamps has allowed the replacement of the gas mantle to be achieved using solar-electric systems which charge batteries by generating an electric current directly from sunlight. In the northern latitudes of Scotland and Isle of Man, the solar panels can make use of the diffused light through the cloud cover and the battery is of a size to accumulate sufficient energy in the summer and autumn months to ensure winter operation. The power consumption for the typically required light range of 18 miles has decreased in the last decade from over 100 watts to 35 watts, making use of highly efficient lamp drivers operating directly from the 24 volt battery supply. Supplementary power for monitoring purposes is supplied from small wind powered generators.

"To ensure that all Aids to Navigation operate correctly, NLB aim to monitor the performance by using land-line and cellular telephone or radio links connecting the light to the NLB monitor centre in Edinburgh. Any malfunction can be immediately advertised to marine users using the Internet or maritime information systems."

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