Polymer dielectrics are in use in a variety of applications in active or passive electrical components. Their propensity to store electrical charges is used e.g. to form electrets but is a drawback when insulation properties are looked for. It is therefore essential to investigate the traps characteristic for a given material because trapping phenomena control the transport properties and therefore the field distribution. Different trap spectroscopies are available to infer the nature of traps, their energy depth and their amount. In the first part of this communication, we briefly review the different methods for traps characterization, emphasizing on strength and weaknesses of the methods. In a second part, results obtained on bioriented polypropylene are used to illustrate the difference in trap depth estimation obtained using thermal and optical excitation to release charges from traps. The differences are discussed with introducing results from luminescence induced by charge recombination.