The influence of light radiation on the thermal change of SnI2 thin films heated at 50, 100 and 150 degrees C in air for 6h was investigated using weight measurement and X-ray diffraction analysis. The thermal change was accelerated by heating and light radiation. Radiation with a tungsten lamp (500 W, 25 cm from the film) was more effective than room light (mainly from fluorescent lamps). Weight loss at 150 degrees C stopped at 21.1% and 21.5%, based on specimen weight, under radiation from room light and from a tungsten lamp, respectively. These values approximately agree with the 20.2% expected for the reaction proposed in our previous papers (Thermochim. Acta, 232 (1994) 29-36; 37-45), 2SnI(2)(s) + O-2(g) --> SnI4(g) + SnO2(s). This reaction mechanism is supported by the presence of diffraction peaks for SnO2. The higher values of the apparent end point (25.0% and 25.5%) at 100 degrees C are interpreted as indicating incomplete evaporation (sublimation) of SnI,.