A differential reflectometer that is capable of measuring small differences in optical reflectivity or transmissivity of two specimens and therefore enhances the structure in the spectral reflectivity of materials was used to study various α-Cu-Zn, α-Cu-Al, and Cu-Ni alloys with the aim of investigating the changes in band structure as a function of composition. In Cu-Zn and Cu-Al alloys three main absorption peaks were identified that were associated with the Δ5 → Δ1, X5 → X4' and L2' → L1sitions. It was found that the Δ5→ Δ1transition increases slightly in energy with increasing Zn or Al concentration. These transitional energies are identical for both alloys in the entire α-phase region. The X5 → X4' and L2' → L1 transitions decrease in energy with increasing solute concentration. The shift in energy is significantly larger for the Cu-Al system. In Cu-Ni alloys no shift of the absorption edge around 2.2 eV was found, which is consistent with the predictions of the virtual-bound-state model. © 1973.