Term applied to works of art concerned with real and apparent movement. It may encompass machines, mobiles and light objects in actual motion; more broadly, it also includes works in virtual or apparent movement, which could be placed under the denomination of Op Art. Kinetic art originated between 1913 and 1920, when a few isolated figures such as Marcel Duchamp, Vladimir Tatlin and Naum Gabo conceived their first works and statements to lay stress on mechanical movement. At about the same time Tatlin, Aleksandr Rodchenko and Man Ray constructed their first mobiles, and Thomas Wilfred and Adrian Bernard Klein, with Ludwig Hirschfeld-Mack and Kurt Schwerdtfeger at the Bauhaus, began to develop their colour organs and projection techniques in the direction of an art medium consisting of light and movement (1921–3). Although László Moholy-Nagy and Alexander Calder pursued more or less continuous artistic research into actual motion in the 1920s and 1930s, it was only after 1950 that the breakthrough into kinetic art, and its subsequent expansion, finally took place.