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