Continual Mobile, Continual Light 1963 is a kinetic relief by Argentinian-born artist Julio Le Parc. The work is composed of seven 1240 mm transparent nylon threads suspended vertically in an evenly spaced row from a thin metal plate that projects from the top of a square wood backboard that is painted white. The threads hang loosely to form another smaller internal square and on each thread is suspended seven mirror-plate squares. As the nylon threads are suspended from one point only, they move quite freely in any air currents, creating powerful optical effects against the static white of the background. On the back of the work is inscribed the work’s title, date and city of production (‘Continuel-mobile | Continuel-lumière. | Le Parc | Paris 1963’) along with the following instructions: ‘Emplacement ideal | sur un mur noir | dans l'ombre avec | une lumiere rasante’ (‘Ideal placement | on a black wall | in a room with | raking lights’). Also attached are two diagrams for installation, showing how the work should be lit with raking light from both sides.

https://www.tate.org.uk/art/artworks/le-parc-continual-mobile-continual-light-t00678