The optical constants n and k are determined for p-type silicon at the Eo and El and critical point energies for one MeV electron irradiated samples. The value for fluences of 1014 and 1016 e−/cm2 are compared to samples before irradiation. The real, ε1 and imaginary,ε2 components of the dielectric function, ε, used to find n and k, were obtained by measurement of tanψ and δ using spectroscopic ellipsometry (SE). The data show that changes in δ, in particular, are greater in the region about Eo than of E1. This is consistent with electrolyte electroreflectance (EER) results in which the Lorentz line shape is narrower for Eo than for E1. The value of n is found to increase and k to decrease with e- radiation at the critical points, although, neither does so monotonically. The change in n at the Eo critical point is greater than at the higher energy main structure E1 whereas, k is a slower varying function in this region.