The visibility aurve and the spectral energy distribution curve of light emitted by semiconductor diodes are approximated by Gaussian functions with appropriate parameters. The buminous efficiency and both power and quantum efficiencies of luminescence of LED can then be evaluated by direct integration when the total luminous flux was measured. Comparison of the calculated values with those obtained by means of planimeter shows fairly good agreement for three kinds of LED: GaP. GaAs0.62P0.38 and Ga0.68Al0.32As.