When parallel light is reflected from a small perfect reflecting sphere the illumination is approximately independent of the angle of incidence and reflection. A formula is developed to study this approximation. Also a formula is given for the case of a sphere which is not supposed to be perfectly reflecting but reflects according to some law like Fresnel’s reflection law.
EUGENE M. BERRY, "THE REFLECTION OF LIGHT FROM A SPHERE," J. Opt. Soc. Am. 7, 679-679 (1923)