Integral fluence spectrum for GLEs from 1956-2017. Each line is a band fit (see Eq. (2)) to the values presented in Table 1. The orange range depicts the worst-case estimated integral fluence spectrum for the lower and highest re-calibrated F_SXR values of the associated solar flares for GLE71 (lower) and GLE65 (higher). We note that the results are represented by their obtained PL fit, per case, excluding the according error estimates.