A method comprising receiving data representing light intensity values corresponding to a flicker pattern of a reference light source powered by an alternating current (AC); operating a controllable illumination source, based, at least in part, on said data; capturing, using an imaging device, a sequence of images of a scene illuminated, at least in part, by said controllable illumination source; estimating an intensity value for at least one pixel in said array, correspondingly in each of said images in said sequence of images; and determining a temporal point in said flicker pattern of said reference light source, based, at least in part, on said estimating.