Techniques are disclosed for generating quality renderings of volumes by sampling a volume light by generating and analyzing a sparse voxel octree. In one embodiment, a volumetric light source may be divided into voxels and importance information stored in an octree. An importance value may be determined for each voxel based on the amount of emitted light in the region associated with that voxel. Importance values regarding the individual voxels may be stored in the leaves of the octree. Each interior node may be associated with an importance value equal to the sum of the importance values of its children. The root node may be associated with the total importance of the entire octree.