Formally published lists of lighted navigational aids date from the nineteenth century. Amongst the earliest was an Admiralty List of Lights published in 1832 that dealt only with lights in the British Isles. As early as 1847 the publication had been extended to cover North American lights, although this included only British North America. Starting in 1861, Alexander Findlay [7] published an annual series of light lists that are regarded by some as more inclusive and systematic. It was not until the late 18th or early 19th century that various national bodies formally took charge of lighted navigational aids with authority vested in them by their governments. In time, these bodies published their own detailed lists of navigational aids within their own jurisdiction.

Today, there are several publications that provide lists of information about navigational aids on an International Basis. In the USA, the National Imagery and Mapping Agency (NIMA) publishes such a list in six volumes [8], as do the French Service Hydrographique et Océanographique de la Marine [9] and the Royal Navy in its Admiralty List of Lights and Fog Signals, abbreviated here as ALL [10]. Similar publications are published in both Japan and Russia. The current ALL is in 11 volumes, A to L inclusive, and covers the entire coastline of the world where it is associated with seawater. It does not include fresh water lights, so the Great Lakes of the USA and Canada, for example, are not included, neither is the IJsselmeer in the Netherlands. It is interesting to note that there is no ALL Volume I, because of the ambiguity for a human between three parameters: the printed symbol for a letter I, a Roman numeral I or a number 1. Since the alphanumeric I is used for both the letter and the Roman numeral, the computer cannot distinguish between them, although it can easily distinguish between an I and a 1 (providing the human keys in the correct symbol). There are many examples in which mixed number-letter combinations demand that certain symbols are not used because humans (not computers) get them confused. Again, I and 1, together with O and 0 are the prime culprits.

Every item listed in the ALL is a navigational aid bearing at least one light. Each entry is allocated a unique number that is almost never changed. When a light is discontinued, the number is dropped from the list. In some cases, it may be reassigned later to a new navigational aid established in the same vicinity, but as a rule, new numbers are created when new navigational aids are put in place. These designations are extremely useful for the purposes of cataloguing the lights of the world, since modern methods use databases that rely upon unique identity tags.

Readers of the ALL are not, however, able to identify the entries that relate to lighthouses, underlining the point that entries in lists of lights are concerned with their importance as navigational aids, rather than the annals of social history. By definition, the ALL, with its title, "List of Lights and Fog Signals", is not a list of lighthouses, nor does it attempt to differentiate or specify what should be regarded as a lighthouse. It does attempt to distinguish major lights from minor lights by use of a bold font when the light is visible for 15 nautical miles or more, but this is because of their importance as lights, not for any architectural significance. There is no way of identifying lighthouses by studying the ALL. There are many beautiful structures of interest to pharologists that are recorded as visible over distances far less than 15 miles and which are not easily distinguishable from other navigational aids having little architectural significance.

The ALL contains a field entry under the heading of "Description", from which you might think it possible to identify those records of lighthouses. Analysis shows that there is no consistency in the descriptions given. Therefore, by the standards set in this internationally recognised and authoritative publication, there is no unambiguous method used to describe a structure.

Table 1 gives a list of sample descriptions used. Each description is comprised of a number of words that are combined to describe the entry. These can be broken down into a number of elements: colour, construction material, shape, and element. If we exclude the adjectives from the description and focus on the noun applied to the lightstructure, (see discussion below) we find such words as:

tower, column, pole, tripod, house, hut etc.

Notable by its absence is the word ‘lighthouse’. The structure might consist of a tower and a building or a tower on a building. It might be a tower with a red lantern or a tower with a red cupola or a tower with a red top. We believe there is no intrinsic difference between these and when the description is tower with red top, it could be either a tower with a red lantern or a tower with a red cupola – i.e. the lantern or cupola being on top of the tower - or a tower with the top part of the tower painted red (but with the lantern of a different colour?) In this way, you can see that the contents of the description field are, again, ambiguous or fuzzy, and not therefore reliable descriptors.

You might consider a church steeple or any other prominent building to be a navigational aid, for if it can easily be recognised from the sea then it assists the mariner in knowing his location. Indeed, such landmarks are shown explicitly on marine charts, and in texts known as coastal pilots, that are popular with sailors today. While these structures were not built specifically to act as navigational aids, they may have been given a light so that they could serve as an autonomous light or as a rear leading light.

The St Phillips Episcopal Church in Charleston, South Carolina, was listed in some international and national lists at the turn of the twentieth century, but is not included in official lists of lights today. However, some lights of this type are officially listed today. In the ALL, Beauvoir (G1139) is a church in Argentina, as are Puerto Bolivar (G3029) in Ecuador and Kihelkonna Rear (C3715.1) in Estonia, for example.

In addition to churches, other buildings have been used in this way. The Hibernia Bank building in New Orleans was listed for a few years after WWI, and actually had a lantern on its roof. The Kingsborough Community College in the New York City area is still listed by the US Coast Guard. The Titanic Memorial Lighthouse, also in NYC, was listed from 1913 to 1967 [11] when it was located at the Seamen’s Institute – it is now at the South Street Seaport.

Other structures that act as aids to navigation are bridges with lights to mark a channel into a harbour, or in a river, as well as offshore oil and gas production platforms in the North Sea, the Gulf of Mexico, or the Arabian Sea, for example. Among the more unusual structures listed is H0026, a light shown from the top of a grain elevator in Churchill, Manitoba.