Cultural Heritage in the Baltic Sea States           In ancient times open bonfires were used to guide mariners. Medieval improvements included the use of towers built from stone or wood to raise the height of the fires, and the use of lever beacons with braziers. The development of optics from the late eighteenth century brought about a number of rapid improvements to lighthouses. The earliest systems used several oil lamps and reflectors to form a parallel beam of light. In 1822 Augustin Fresnel (1788-1827) invented a lens that used multiple glass prisms to bend the light into a powerful central magnifying glass. His invention was so successful that many of these lenses are still in use today. The first steps towards automation began in 1906 when Gustaf Dalén (1869-1937) invented a flashing acetylene gaslight. He later developed the first reliable device for automatically operating lights from sunset to sunrise and received the 1912 Nobel Physics Prize. Hemp, oil, paraffin, gas, petrol and electricity have all been used as energy sources for lights. Today solar power and radioactive isotopes are also used. Photocells now switch the lights on and off as required. In 1995 a new means of lighting was established in Estonia. Energy saving diodes were brought into use that no longer require an optical lens and last for at least 10 years.         A replica lever beacon, at Finland’s Maritime Museum. © Markku Heinonen, Maritime Museum of Finland. Kõpu built in 1531 on the Estonian island of Hiiumaa (Dagö) is one of the oldest Baltic lighthouses still in use. © Danckert Monrad-Krohn. The gas operated lens system that was in use at Bengtskär between 1968 and 1983. © Jukka Grönlund, Finnish Maritime Administration.         © Polish Maritime Museum