Ships bound for the new northern ports of Mackay and Bowen faced a cruel choice. The open ocean outside the reef offered no shelter if a vessel lost its rudder or sprang a leak; the Inner Passage, the sheltered lane between the coast and the reef, was safer in a crisis but utterly unlit. As early as 1864 a Legislative Council committee noted that traders from India and China were avoiding Queensland's north altogether rather than risk the dark. The case for a light was made formally in 1876 by George Poynter Heath, the colony's first Portmaster. The contract went to W. P. Clark, who had already built Queensland's first lighthouse at Bustard Head, for the sum of 3,195 pounds. Its lens, a revolving dioptric ground by the celebrated Chance Brothers of Birmingham, threw a beam visible 14 nautical miles out to sea.

The cay is tiny, so the station was built tight: the conical tower at the centre, the keepers' cottages and storehouses arranged around it like spokes on a wheel. The design was deliberately humble - a timber skeleton sheathed in riveted iron plates, lit inside not by windows but by ship-style portholes. It was the fourth Queensland lighthouse of this prefabricated type, and the first to use those portholes. Humble, but durable: the original 1878 tower still stands, though every other early structure has been lost. In March 1911 a cyclone tore across the island, stripping away its soil and vegetation and battering the buildings - a reminder of the forces this small iron cylinder was built to outlast. The keepers tended the flame through it all, upgrading from oil wick to kerosene in 1923, to electricity in 1963, and at last to solar power in 1993, when the station was automated and the last human watch came to an end.

In July 1928 the lighthouse gained unusual company. A party of scientists led by the British zoologist Maurice Yonge landed on Low Isles and made it their home for thirteen months, in what became the first sustained scientific study of a coral reef anywhere in the world. The team of a dozen included Yonge's wife Mattie, who served as medical officer, and several pioneering women researchers among them Sheina Marshall and Anne Stephenson. Camped beside the keepers, they dissected the partnership between coral and the algae living within it, mapped the reef, and laid foundations that reef science still builds on today. Their seven volumes of findings remain reference works. For thirteen months the modest light that guided ships also lit the birthplace of a whole field of knowledge.

The last keeper left in 1994, but the island did not fall silent. When automation was announced, locals formed the Low Isles Preservation Society to defend the place, and one of the rebuilt cottages now serves as a research station, its laboratory carrying on the work Yonge began. The original Chance Brothers lens, retired in 1993, is on display in the Court House Museum at Port Douglas, where you can stand close to the glass that once swept the reef at night. The cay itself, ringed by coral and shaded by its lighthouse, is a favourite day trip from Port Douglas and Cairns - reachable only by boat, the tower closed, the light still turning faithfully every ten seconds over the channel it was sent north to guard.