An apparatus and a method for shaping a light spectrum are presented. The apparatus includes a spatial light modulator (140) provided for shaping the spectrum of a primary beam. The spatial light modulator (140) includes an array of cells in which each cell is operable in a first state and a second state. The apparatus also includes a controller (160) configured to change the state of a subset of cells iteratively, based on a stochastic process, to shape the spectrum.