The growth rate of F‐centres as a function of the time of X‐irradiation and the thermoluminescence (TL) of X‐ray colored cesium halides have been studied. In the case of CsCl and CsBr the effect of cadmium impurity is to suppress the growth of the F‐band. The first stage growth of F‐centres has been analysed into further ‘exponential’ substages. The first stage in CsBr consists of at least two substages whereas the analysis of CsCl crystals yielded only one substage for the first stage. Two TL glow peaks have been found in X‐irradiated CsBr at 110 and 125 °C. The results suggest that these are due to the recombination of the F‐centre electrons with holes. In CsCl, the TL glow peaks attributable to F‐centres are observed at 100, 120, and 135 °C. In Cd‐doped crystals new glow peaks have been observed which have been attributed to centres involving Cd‐impurity, by comparison with optical absorption studies. The trap depths of the glow peaks have been evaluated using the ‘initial rise method’.