Worked example - linear Stark splitting of hydrogen n=2. The splitting between extreme components is delta-E = 3 e a0 E_field. Step 1: e = 1.602 x 10^-19 C, a0 = 5.29 x 10^-11 m. Take E_field = 10^6 V/m (a strong lab field). Step 2: delta-E = 3 x 1.602 x 10^-19 x 5.29 x 10^-11 x 10^6 = 2.54 x 10^-23 J. Step 3: convert to eV: /1.602 x 10^-19 = 1.59 x 10^-4 eV = 0.16 meV. Tiny - yet spectrometers resolve it easily, which is why Stark spectroscopy can measure electric fields as small as those inside a flame or plasma.