An optical system for measuring the slope of random wind‐generated water waves is described. The instrument employs the refraction of a vertical light ray, which is a technique that has been previously used. The present system, however, employs a large‐area array of individual photovoltaic cells to measure the refraction angle of the beam. Because the array provides a much larger active area with no preferred direction, it is much better suited to the measurement of random water wave fields, typical of those generated by wind.