An explanation of the Lamb shift is presented by Bethe.

The experimentally measured Lamb shift has been argued to be, in part, a zero-point energy effect.

Lamb shift of positions of atomic levels.

The Lamb shift is proportional to α and its measurement yields the extracted value:

Indeed, as demonstrated by Hans Bethe, the Lamb shift necessitated a self-energy term to be explained.

The Darwin term makes the s-state and p-state the same energy, but the Lamb shift makes the s-state higher in energy than the p-state.

Their indirect effects can nonetheless be measured, and their existence has been confirmed by a small shift (the 'Lamb shift') they produce in the spectrum of light from excited hydrogen atoms.

The Lamb shift is a small difference in the energies of the 2 S and 2 P energy levels of hydrogen, which arises from a one-loop effect in quantum electrodynamics.

Predictions of QED vacuum such as spontaneous emission, the Casimir effect and the Lamb shift have been experimentally verified, suggesting QED vacuum is a good model for a high quality realizable vacuum.

One of the founding fathers of QED, Richard Feynman, has called it "the jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the electron, and the Lamb shift of the energy levels of hydrogen.