In cathode‐ray excitation of a phosphor the energy of the fast electrons appears, in an intermediate stage, as excitation of the valence shell electrons. We have used photons of energy up to 25 eV to simulate cathode‐ray excitation. Attempts to account for cathode‐ray efficiencies on the basis of the photoexcitation efficiencies give agreement in some cases and substantial lack of agreement in others. A correlation between high plasma resonance energy and low cathode‐ray efficiency is pointed out.