Abstract The amount of activators, which are now used for the present phosphors, was determined by means of polarography. The results obtained shows that manganese or copper is not dissipated during firing, while antimony or lead is dissipated in that period. As for calcium silicate phosphors activated by manganese and lead, the residual amounts of activators were analysed by polarography and, these amount being taken as the additional factorial effects, the analysis of covariance was carried out to see the effects of atmosphere and firing time on the brightness. The results obtained show that the amount of lead has a more significant effect upon the brightness than manganese and the change of atmosphere causes that of the amount of activators and the brightness.