A method and an apparatus for controlling exposure of a surface of a substrate in a process of structuring the substrate with light of a predetermined intensity are described, wherein the light is directed to the surface by means of a deflectable mirror. The intensity has a first maximum at a first deflection of the deflectable mirror, a first minimum at a second deflection of the deflectable mirror, a second maximum at a third deflection of the deflectable mirror, and a second minimum at a fourth deflection of the deflectable mirror. A signal representing the predetermined intensity, and a signal representing a threshold intensity are received, the threshold intensity being equal to or less than the intensity of the second maximum. It is determined whether the predetermined intensity is greater than the threshold intensity. The deflection of the deflectable mirror is controlled to be between the first deflection and the second deflection when the predetermined intensity is greater than the threshold intensity, and to be equal to or greater than the third deflection when the predetermined intensity is equal to or less than the threshold intensity.