Grimaldi was born at Bologna, Italy, and became a Jesuit. In 1648 he became professor of mathematics at his order's college in his native city, where he acted as assistant to Giovanni Riccioli. His discovery of the phenomenon that he named the diffraction of light was reported in his posthumous work Physico-mathesis de lumine, coloribus, et iride (1665; Physicomathematical Studies of Light, Colors, and the Rainbow). He showed that when a beam of light passed through two successive narrow apertures, the pattern of light produced was a little bigger than it should have been if the light had traveled in an absolutely straight line. Grimaldi considered that the beam had bent outward very slightly, indicating that light must have a wave nature. The result presented difficulties to all 17th-century corpuscular theories of light.