An experimental apparatus for studying the emission spectra of helium discharge plasmas is described which provides the required spatial and time resolution. The gas temperature of the plasma was determined from the intensity distribution of the rotational structure. In the diffusive discharge regime the positive column is stationary and the measured values of the temperature agree with those calculated from the energy balance equation. In the contracted regime, a modulation of the gas temperature is observed at a frequency equal to the frequency of the periodic variation in the emission intensity caused by stratification of the contracted column.