A method for operating an optical sensing device having a light source and a photodetector device with at least one photosensitive element. A surface portion is illuminated with radiation by the light source and the radiation reflected from the illuminated surface portion is detected with a photosensitive element. While said surface portion is being illuminated, an output signal of the photosensitive element over time is integrated, the output signal integration level is compared with a first integration reference level during integration; the integration step is interrupted if the output signal integration level has reached the first integration reference level, or the comparison step is repeated until a first integration period has elapsed if the output signal integration level has not reached the first integration reference level.