This paper introduces an efficient hierarchical algorithm capable of simulating light transfer for complex scenes containing non-diffuse surfaces. The algorithm stems from a new formulation of hierarchical energy exchangesbetween object clusters, based on the explicit representation of directional radiometric distributions. This approach permits the simplified evaluation of energy transfers and error bounds between clusters. Representation and storage issues are central to this type of algorithm: we discuss the different choices for representing directional distributions, and the choice between explicit storage or immediate propagation of directional information in the hierarchy. The framework presented is well suited to a multi-resolution representation, which may in turn significantly alleviate the storage problems. Results from an implementation are presented, indicating the feasibility of the approach and its capacity to treat complex scenes