Since 1973, Franco-Argentinian artist Jorge Orta has been compiling an alphabet made up of universal human symbols. But rather than paint these onto canvases or publish them in books, Orta uses light cannons - giant projectors that cast light over an area of 10,000 square metres at a distance of up to a kilometre - to project his "luminographies" onto vaarious sites, including Incaa ruins at Machu Picchu, Chartres Cathedral, the volcano of Aso in Japan and Saint Mark's Cathedral in Venice.