The methyl ammonium lead halides are promising visible-light absorbers for application in solar cells. The most common synthetic routes use the solid binary halides as one of the starting compounds. These binary lead halides exhibit photodecomposition. In view of the perovskite crystal structure of the methyl ammonium lead halides, it is possible that also here the lead halide parts may exhibit photodecomposition. The mechanism of the photodecomposition of the binary lead halides is presented in detail. Based on this mechanism the trapping of photo-generated electrons on the lead ions in these perovskite materials should be studied in detail. (C) 2014 Published by Elsevier B.V.