Ile Vierge Lighthouse is tallest stone lighthouse in Europe, and the tallest "traditional lighthouse" in the world. The International Hydrographic Organization specifies Ile Vierge as marking the south-western limit of the English Channel. The lighthouse is 82.5 metres (271 ft) tall, made of blocks of granite. The external face is a truncated cone; the interior face is cylindrical, lined with 12,500 opaline glass tiles. There are five steps to the front door; inside, 360 steps of stone and 32 of iron lead to the lamp platform. The electric lamp was installed in 1952 on the original mechanical turning plate, sitting in a bath of mercury. The plate was replaced with an electric motor in 1983. The lamp has four lenses with a focal length of 0.5m. The twin beam gives a white flash every 5 seconds, visible for 27 nautical miles (50 km; 31 mi). Electrical generators were installed in 1959, supplemented in 1967–1994 by two wind turbines. The light and rotation are activated automatically by a photoelectric sensor. Although the lighthouse is automated, the site is still manned. The island is open to the public from April to September, as is the lighthouse, by appointment.