The diagram represents the electromagnetic fields of a single photon with wavelength l propagating at velocity c. The green indicates that the electric field is pointing outward from the central axis perpendicular to the propagation direction. The blue indicates that the electric field is pointing inward toward the central axis. The arrows on the surface indicate the magnetic field B and its direction which is angular about the central axis. The surface itself represents the energy in the electric and magnetic fields where the volume of every cross-sectional segment perpendicular to the central axis is proportional to the total energy for that segment.