Abstract: A pair of light intensity detectors are spaced apart in range and an arrangement is included for reflecting light from a target to the detectors. The system measures target range by dividing the output signal of one of the detectors by a signal which is a function of the difference between the output signals of the two detectors to produce a quotient signal. To avoid low signal instability problems, the difference signal is generated in one embodiment of the system by subtracting only a selected fraction of the output signal of the far detector from that of the near detector. A substantially linearized output signal representing target range is produced in this system embodiment by raising the quotient signal to a selected power. The light detectors are preferably incorporated in input circuits which are temperature compensated.