A line shape model that accounts for low‐frequency fluctuations is applied to the Balmer series of the hydrogen isotopes (atomic transitions n → 2). The plasma fluid parameters (density, temperature, etc.) are described as random variables characterized by a prescribed joint probability density function. A special emphasis is devoted to Stark broadened lines, which are sensitive to the plasma density. It is shown that fluctuations can lead to a significant increase of the line width if the fluctuation level ΔNe/〈Ne〉 (with 〈Ne〉 and ΔNe being respectively the density averaged along the line‐of‐sight and its RMS value) is large. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)