Electron densities in two types of atmospheric pressure radio frequency plasma sources: dielectric barrier discharge (DBD) and discharge with bare electrode (DBE) are investigated by analysis of Stark broadening of Hydrogen Balmer (Hβ) lines. Voigt fitting is firstly employed to obtain the electron density below the theoretical lower limit of 1020 m-3. Fine-structure fitting method is further applied to verify the electron density for both plasma sources. When injecting power from 4 W to 20 W, the electron densities are found in the range of 2.9-6.1×1019 m-3 and 3.6-8.6×1019 m-3 for DBD and DBE, respectively. The electron density study aims to gain more insight of the physics of cold atmospheric pressure radio frequency helium plasma
