As such, the energy of a photon being absorbed or emitted by an atom which causes an electron to jump from nj to ni is
where h is Planck's constant, c is the speed of light and λ is the wavelength of the photon. The ionization energy is the energy needed to completely remove an electron, or when ni = ∞. Assuming the atom is in its ground state (nj = 1), this is simply 13.6 eV.
The above equation can be written as
is known as the Rydberg constant.