Abstract: Caustics produce beautiful and intriguing illumination patterns. However, their complex behavior make them difficult to simulate accurately in all but the simplest configurations. To capture their appearance, we present an adaptive approach based upon light beams. The coherence between light rays forming a light beam greatly reduces the number of samples required for precise illumination reconstruction. The light beams characterize the distribution of light due to interactions with specular surfaces (specular light flux) in 3D space, thus allowing for the treatment of illumination within single-scattering participating media. The hierarchical structure enclosing the light beams possesses inherent properties to detect efficiently every light beam reaching any 3D point, to adapt itself according to illumination effects in the final image, and to reduce memory consumption via caching.