Sketch of a 2D horizontally infinite prominence model illuminated from the solar surface at its sides and the bottom. On the right is a close-up view of the model cross-section divided into voxels. For each voxel, the nearest surface of the model is indicated by a colour. For yellow voxels, the nearest surface is at the bottom of the model, receiving the illumination from the entire solar surface. For red voxels, the closest surface is at the sides, receiving the illumination from half of the solar surface. For the blue voxels, the nearest surface is at the top, where there is no illumination from the solar surface.