Controlling caustics

Caustics are captivating light patterns created by materials focusing or diverting light by refraction or reflection. We know caustics as random side effects, appearing, for example, at the bottom of a swimming pool, or generated by many glass objects, like drinking glasses or bottles. In this paper we show that it is possible to control caustic patterns to form almost any desired shape by optimizing the geometry of the reflective or refractive surface generating the caustic. A seemingly flat glass window, for example, can produce the image of a person as a caustic pattern on the floor, generated solely by the sunlight entering through that window. We demonstrate how this surprising result offers a new perspective on light control and the use of caustics as an inspiring design element in architecture, product design and beyond. Several produced samples illustrate that physical realizations of such optimized geometry are feasible.