Hydrogenated amorphous silicon-carbon alloy films were prepared by the glow discharge decomposition of silane and ethylene. The real and imaginary parts of the dielectric constants epsilon(1) and epsilon(2) of the film were determined at room temperature for the photon energies between 1.38 and 4.86 eV for the as-deposited (T-s = 250 degrees C) as well as for subsequent anneals at different temperatures up to 1200 degrees C. The optical bandgap (E-opt) was determined from the Tauc’s relation while the characteristic optical parameters such as the dispersion energy (E-d), average excitation energy (E-o), plasmon energy (<(h)over bar w(p)>) and the valence electron density (n(v)) were obtained from the Wemple-DiDomenico model. We observe an interesting correlation between E-opt and n(v) which seems to indicate the coupling of the valence and conduction band through single-particle excitation.