  We present a novel algorithm for light source estimation in scenes
reconstructed with a RGB-D camera based on an analytically-derived formulation
of path-tracing. Our algorithm traces the reconstructed scene with a custom
path-tracer and computes the analytical derivatives of the light transport
equation from principles in optics. These derivatives are then used to perform
gradient descent, minimizing the photometric error between one or more captured
reference images and renders of our current lighting estimation using an
environment map parameterization for light sources. We show that our approach
of modeling all light sources as points at infinity approximates lights located
near the scene with surprising accuracy. Due to the analytical formulation of
derivatives, optimization to the solution is considerably accelerated. We
verify our algorithm using both real and synthetic data.
