A methacrylate sculpture made in four versions (inv. 936, 1156, 3417, 3418) in the same shape and size but different colours and transparency, Colonna di luce was custom-made for the ‘Cinema a luce solida’ (Solid-Light Cinema) exhibition at the De Nieubourg Gallery in Milan in 1968. Placed on the gallery mezzanine, the sculptures were positioned under ceiling-mounted light bulbs, filling the empty space between light source and floor, as if crystallising the light beam, making it ‘solid’ – the concept around which the exhibition revolved.