A standing wave can be produced in a guitar string where the wavelength of the wave is the same length as the string (I believe this is referred to as the first harmonic) and where the string is an exact multiple of the wavelength of the wave (referred to as the second and subsequent harmonics). A standing wave of light can apparently be produced by propagating the wave between two mirrors placed an exact multiple of the light's electromagnetic wavelength apart. I first thought this principle might be used in a laser but later realised the waves didn't need to exactly superimpose to increase the intensity of the resulting laser beam of light. My thoughts then turned to electromagnetic waves more generally - under what circumstances (if any) would an electromagnetic wave be able to achieve a standing (presumably spherical) form bound by the strength of its own electric and magnetic fields (while sound propagation requires a medium such as a guitar string, electromagnetic waves can propagate in a vacuum)? Can the strength of the electric and magnetic fields ever be great enough to bound particular electromagnetic (presumably shorter) wavelengths ? Some secondary questions are: Would such a standing wave also support multiple harmonics ? Noting that the "v" in v=fγ refers to speed rather than velocity, would the speed of such a standing electromagnetic wave still be "c" even though it may propagate circularly? I Assume the formula breaks down somewhere in that if you propagate a wave with infinite energy and the frequency becomes infinite, presumably the wavelength would become zero and the speed also would then become zero (ie you pour enough energy in and the wave just disappears like a black hole). While electromagnetic waves are considered to have duality the energies of the wave and particle form are supposedly linked by the same formula - assuming that there could exist standing wave forms of electromagnetic waves, perhaps that is what a photon is ?