Abstract: A solar protection device includes slats of refractive material rotatable about a longitudinal axis, having an even, flat upper side and having on their lower side prisms arranged serially without gaps and running parallel to the longitudinal axis. In order to maintain the condition for retroreflection with variations of the sun's position, the angle of inclination to the horizontal of the slats must be readjusted from time to time, at least seasonably. For automatic adjustment thereof a light sensing arrangement of two light sensors arranged oppositely on both cathetal legs of one of the prisms whose hypotenuse is formed by the upper side of the rotatable slat. Control by a drive and associated electronics is undertaken and continued as long as solar rays impinge on one of the light sensors with intensity exceeding a predetermined illumination level.

Abstract: A signal generator equipped with a shading device and two light sensors is arranged on the upper side of a slat equipped with retro-reflective prisms and rotatable about a longitudinal axis. Depending upon the sun's position relative to the slat, the light sensors are variously shaded or illuminated by means of the shading device, and when the slat is rotated about its longitudinal axis, the light sensors supply electrical code values which change in opposing directions. A difference between the code values is fed via an amplifier to a servo-motor which rotates the slat about its longitudinal axis until the plane of incidence of the sun's rays, which passes through the longitudinal axis, is at right angles to the upper side of the slat. This ensures that sun's rays which hit the slat are reflected regardless of the sun's position, the time of year, and the alignment of the facade plane in which the slat is arranged.