(accepted, be published in Phil. Mag. B,1998)
Transients related to photoconductivity, photodielectric and photoabsorption changes were simulated for a multiple trapping model including monomolecular recombination using a linear and a rectangular distribution of localized states. These two distributions provide the same behavior, which differs from the exponential distribution. The nature of the transients depends on the relative time constants in the process and can be categorized into regions of weak, intermediate and strong retrapping. The well-known power law behavior is obtained only for a limited set of conditions, and it is shown that the exponential tail has a time constant that is related to the release time of the deepest trap.