Secondary waves of electroluminescence exhibit specific trends with varying frequency and temperature. As has been assumed before, secondary waves are caused by effects of charge polarization inside the phosphor crystals; however, there has been no previous theoretical approach to this problem which leads to a description of the behavior of secondary waves with respect to frequency and temperature. An attempt has therefore been made to treat this phenomenon mathematically, using a simple model of charge polarization. During electroluminescent excitation conduction electrons are drawn to the anodic crystal parts where they become trapped. When the alternating field externally applied passes zero these electrons, under the influence of a polarization field, may return to luminescence centers and thus give rise to light emission. The return process depends on the trap depth, the temperature, the applied external field, and its frequency. This model can indeed describe the observed behavior, so that there seems to be little doubt as to the actual origin of secondary waves. As an interesting corollary of these considerations, the occurrence of secondary waves may be a means for determining electron trap depths and for detecting shallow traps where ``glow curves'' fail.