Optical transmission measurements provide a detailed picture of redistribution of the c-axis spectral weight of La2−xSrxCuO4 (x=0.12, 0.15) and allows to examine the Ferrell–Glover–Tinkham (FGT) sum rule up to 1.8 eV. A new conductivity peak is observed below Tc at ∼120 meV, which indicates a possible new collective mode and strongly increases the FGT sum rule violation. The absolute value of the violation is larger for the optimally doped sample. The sum rule starts to recover in the range of the low-lying interband transitions (∼1 eV). In the normal state no clear energy scale of the pseudogap can be seen.