An analytical function for the imaginary part of the dielectic constant of microcrystalline silicon is proposed. The function consists of a sum of Lorentz oscillators with Gaussian broadening, and is based on literature data. The real part is numerically obtained by Kramers-Kronig integration. The physical significance of the results is discussed. It is shown that the choice of the minimization procedure may affect the spectral region (low or high absorption) where the accuracy of the fit is optimized. The impact on computed Transmittance data shows the limits of acceptability for the errors in the fit.