An optical random number generator has: a light source (2) for randomly emitting photons (9); an array (3) of single photon avalanche diodes for detecting the photons (9) provided by the light source (2), wherein the array (3) of single photon avalanche diodes is positioned in a predefined distance (d) to the light source (2); and a control (10) coupled to the array (3) of single photon avalanche diodes and for determining an arrival time of the photons (9) detected by each of the single photon avalanche diodes of the array (3) of single photon avalanche diodes, and for generating a random number on the basis of the arrival time.