Round Island Passage Light is an automated, unmanned 1948 lighthouse located in the Round Island Channel in the Straits of Mackinac, Michigan. The channel is a branch of Lake Huron.HistoryThe Round Island Lighthouse was constructed in 1895 to mark the southern side of the Round Island Channel. In 1936, the United States Coast Guard developed plans to construct another lighthouse, 1000 feet south of Mackinac Island, to mark the northern side of the navigable channel. However, World War II intervened, and construction was delayed. In the interim, a buoy with a radio beacon was moored near the site. The Coast Guard began construction on the Round Island Passage Light in 1947, and finished in 1948. Construction included building a control house at the southern tip on Mackinac Island, and running power cables underwater to the light. The lighthouse was equipped with a beacon light, fog signal, and radiobeacon. The light flashed a green signal from an array of sealed beam lamps mounted at the top of the light tower.The Passage Light was one of the last lights to be constructed on the Great Lakes. The light was built at the same time that the 1895 lighthouse was deactivated. In 1959, the lighthouse's beacon characteristic was changed from green to a flashing red light, and the radiobeacon distance-finding system was deactivated in 1962. In 1968 the formerly all-white light was given a red-painted base on a white pier. In 1973 the light was automated, and the steel antenna tower was removed in the early 2000s.