The original structure at Ardnakinna was conceived as a daymark - a tall circular masonry beacon that ships could line up against to find the safe channel into Bantry Bay. It was recommended in 1847, when the Great Famine was emptying the surrounding parishes, and built in 1850 with the granite that the Beara Peninsula produces in such abundance. In 1863 it was 'capped,' which in lighthouse terminology means finished with a roof but not equipped with an actual lantern. For shipping using Castletownbere - already an important deep-water anchorage and naval station - the beacon was a useful navigational mark by day but useless at night. The Admiralty took ownership of the tower in 1902, presumably because of the strategic importance of Berehaven as a fleet anchorage for the Atlantic Squadron, but they too left it dark. In 1923, after the British departure from most of Ireland, the tower was discontinued altogether.

In 1945, a trawler incident at the western entrance to Castletownbere brought the question of a navigation light back into urgent focus. The harbour had become important to Ireland's fishing fleet, and the Berehaven channel - narrow, rocky, and exposed to weather sweeping in from the open Atlantic - was claiming more victims than its peacetime traffic could bear. Requests for navigation lights were formally submitted in 1948. A positive recommendation followed in 1955. Then nothing happened. For another nine years, the Ardnakinna tower stood dark while local fishermen continued to feel their way past it. It took until 1964 for the Minister of Transport to give the project formal approval. The existing tower was identified as the natural location - it was already there, in the right place, structurally sound, lacking only a lantern.

The lamp installed at Ardnakinna in 1965 was secondhand. It was salvaged from a decommissioned lightship - a piece of equipment that had spent its working life moored as a floating beacon somewhere on the Irish coast - and adapted to its new fixed home on Bere Island. The 1,500-watt lantern was given a dual power supply: mains electricity for normal operation, with a diesel generator as backup for the inevitable storms that knock out the grid on this exposed coast. On 23 November 1965, the light was formally turned on for the first time, more than a century after the original beacon had been recommended. The keeper-attendant who looks after Ardnakinna also tends two other automated lights in the area, working from the Castletownbere helicopter base. The lighthouse is now part of the network operated by the Commissioners of Irish Lights, the all-island authority that has run Irish navigation aids since 1867.

The western entrance to Castletownbere matters because the harbour matters. Berehaven is one of the deepest natural anchorages in Europe - capable of holding the entire Atlantic Fleet of the Royal Navy in earlier eras, and today host to one of Ireland's busiest fishing ports. Fishing vessels come in at all hours and in all weather, often with deck cargoes of fish that need to be landed quickly. The Beara coast in poor visibility is unforgiving: rocky headlands, strong tidal currents through the channels between Bere Island and the mainland, sudden squalls that drop the visibility from miles to yards within minutes. The Ardnakinna light, paired with other navigational marks in the area, lets a skipper line up the safe channel and run in on instruments and beacons even when the headland itself is invisible. The history of why it took so long to install reveals something about how slowly maritime infrastructure can move - and how quickly a missing light can be remembered after a wreck.