Abstract: A non-imaging detector for directly measuring the angle of incidence of irradiation in one plane from an illuminating source. The detector includes a slit mask that transmits narrow lines of irradiation across an array of detectors closely underlying the slit mask. The detectors are configured to generate photocurrents whose ratio exponentially increase as the irradiation lines through the slits move along the array in response to changes in angle of incidence. The detectors are configured according to an exponential formula so that adjacent rows of detectors produce photocurrents so that the photocurrent log difference from adjacent rows will result in a signal directly proportional to incidence angle when subtracted by associated circuitry.