A system for generating random numbers comprises a light source for emitting photons, an optical diffuser element, and a plurality of light detector elements, each being for converting received light into electrical charge. The system further comprises means for converting the electrical charge of each of the plurality of light detector elements into an output value. The light source is for illuminating the plurality of light detectors with the photons, whereby the photons are incident on random ones of the plurality of light detectors. The diffuser is located in a light path between the light source and the plurality of light detector elements, and is for making the degree of illumination of each of the plurality of light detector elements more uniform, whereby the output values of the plurality of light detector elements comprise a set of random numbers each comprising quantum noise.