The portion of the neutron flux spectrum responsible for producing radiation damage in the light insulators is identified. A simplified method for describing the radiation damage dosage is devised to permit quantitative comparisons between the radiation damage developed in different reactor facilities. The damage rates in facilities of the following reactors are compared: X-10, CP-3', CP-5, Hanford, BNL-1, and LITR; the relation of the damage rates to various quoted fluxes is indicated. It is shown that the damaging flux has no general relation to the total flux, the thermal flux, the resonance flux, or the epithermal flux; it must be monitored for each experiment.