The time-averaged electromagnetic energy density is the sum of the electric and magnetic energy densities: and . (Note that the fields here represent mean-squared values, hence the additional factors 1/2). The total energy density is given by . For a incoming wave with , the total energy density is (). Taking account of scattering, the energy density fluctuates in space and can locally increase up to double the average value: .

This Demonstration shows the three-dimensional distributions of the energy densities and in the vicinity of the sphere, given the sphere radius and the incident wave frequency . The distributions of and are displayed in red and blue, respectively, in the - and - planes. The variation in density depends on the relative dimensions of the conductor radius and the electromagnetic wavelength . The image refreshes rather slowly, even with the image quality decreased.