  Recovering lighting in a scene from a single image is a fundamental problem
in computer vision. While a mirror ball light probe can capture omnidirectional
lighting, light probes are generally unavailable in everyday images. In this
work, we study recovering lighting from accidental light probes (ALPs) --
common, shiny objects like Coke cans, which often accidentally appear in daily
scenes. We propose a physically-based approach to model ALPs and estimate
lighting from their appearances in single images. The main idea is to model the
appearance of ALPs by photogrammetrically principled shading and to invert this
process via differentiable rendering to recover incidental illumination. We
demonstrate that we can put an ALP into a scene to allow high-fidelity lighting
estimation. Our model can also recover lighting for existing images that happen
to contain an ALP.
