We present an algorithm to automatically estimate three-dimensional light positions from an unordered set of images. We collect images using a single stationary camera while manually moving a light source around an object. Rather than measuring light positions directly, the algorithm extracts a three-dimensional manifold of positions from the images using dimensionality reduction techniques. This obviates the need for calibration and specialized equipment, making our approach inexpensive, portable and applicable to objects of almost any size. We demonstrate our results using image-based relighting applications.