Abstract
A new type of sunshine-duration meter, 1) providing an optical system that consists of a mirror and a photodetector, was recently developed. The photodetector looks sky through a mirror rotating around an axis parallel to that of the earth's. A uniform sensitivity, independent of the incidence angle of the sun, is performed by an optical mirror with two diffusible surfaces. Effect of diffuse skylight has been remarkably well eliminated by an adoption of a pyroelectric detector.
