This paper introduces a new approach to hierarchical radiosity computation, making it practical for the simulation of energy exchanges in very complex environments. Results indicate that the new formulation allows the effective simulation of environments of significant complexity, containing several thousands of surfaces or volumes. In this new technique a hierarchy is constructed in a bottom-up fashion, in effect grouping together nearby surfaces for the purpose of evaluating their energy exchanges with distant objects. This clustering approach eliminates the need for an O(n2 ) initial linking stage, by establishing connections between abstract entities that behave like volumes. A general hierarchical transfer algorithm for volumes is first derived and its adaptation to clustered environments is then discussed. In particular the mechanisms required to efficiently simulate the radiant interactions between surfaces and clusters are reviewed.