The radiation loss in DIVA is measured quantitatively by a pyroelectric detector calibrated by heavily contaminated resistive discharges. The results are: (1) radiation loss power due to low-Z impurities does not play an important role; (2) radiation loss power due to the pseudo-continuum from high-Z impurities affects the power balance of the confined plasma; (3) the time dependence of energy loss channels is clarified in the gross power balance, a fact which attests to the reliability of the radiation measurements carried out by the pyroelectric detector.