2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/78692We prove that the set of visible points of any lattice of dimension at least 2 has pure point diffraction spectrum, and we determine the diffraction spectrum explicitly. This settles previous speculation on the exact nature of the diffraction in this situation, see math-ph/9903046 and references therein. Using similar methods we show the same result for the 1-dimensional set of k-th power free integers with k at least 2. Of special interest is the fact that neither of these sets is a Delone set --- each has holes of unbounded inradius. We provide a careful formulation of the mathematical ideas underlying the study of diffraction from infinite point sets.45 pages, with minor corrections and improvements; dedicated to Ludwig Danzer on the occasion of his 70th birthdayMetric GeometryMathematical PhysicsNumber Theorytext