Electronic devices may include light sensors. A light sensor may be an ambient light sensor that is mounted adjacent to an aperture in an opaque structure. An ambient light sensor may include active light sensor elements located adjacent to the aperture and inactive light sensor elements located adjacent to the opaque structure. Signal processing circuitry may be interposed between the light sensor elements and a summing circuit that sums light signals from the light sensor elements to form an ambient light signal. The signal processing circuitry may include a switch and an amplifier associated with each light sensor element. The switch associated with each element may be used to selectively activate or inactivate that element. The amplifier associated with each element may be used to amplify the light signal from that element by a gain factor that depends on the location of that element with respect to the aperture.