The fractional change in reflectivity due to strain ΔRR of evaporated film samples of four silver-indium alloys was measured in the energy range 2.5-4.5 eV. The films had indium concentrations of 0.4, 1.6, 3.3, and 5.0 at.%. A Kramers-Kronig inversion of ΔRR yielded the change, due to strain, of the phase shift of the reflected electric field. The strain-induced changes of the real and imaginary parts of the complex dielectric constant, Δε1 and Δε2, were calculated. Interpretation of the structure in Δε2 of silver and the four alloys yielded the following conclusions. (a) The structure in Δε2 at 4.06 eV in silver is due to the L2′→L1 (Fermi surface to conduction band) transition and not to the L3→L2′ (d band to Fermi surface) transition as previously suggested. (b) The L2′→L1 band gap in silver is 4.15 eV and decreases to about 3.7-3.8 eV in the 5.0% indium alloy. (c) Indirect transitions contribute to ε2 and Δε2 below the direct L2′→L1 transition energy in the silver-indium alloys.