[en] In a gas mixture consisting of 99.5% of helium and 0.5% of molecular hydrogen, dielectric barrier discharges are generated by applying AC voltage to two electrodes, deposited on the outward surfaces of the ceramic plates. The two ceramic plates made of BaTiO₃ form a slit-like discharge gap of 0.5 mm (distance between the inward ceramic surfaces). The radiation of the hydrogen H_α spectral line emitted from this gas gap is studied, applying gas pressures from 4 kPa to 60 kPa. The H_α line shapes emitted from this gap are measured with spectral and spatial resolution (in the direction perpendicular to the ceramic surface). The light detection system, equipped with a chopper (synchronized with the feeding voltage) allows light polarization sensitive measurements to be performed. The observed large broadening of the H_α profile is attributed mainly to the linear Stark effect. On the basis of analyzed H_α line shapes the electric field strengths in the gas gap at different pressures are determined