Antireflective coatings(增透膜〉 A coating material must have an index of refraction between that of air and the glass to be coated. Where A is the wavelength in min vacuum of the rays that we want pass through the coating n is the refraction index. Antireflective coatings(增透膜） A coating material must have an index of refraction between that of air and the glass to be coated. Where  is the wavelength in vacuum of the rays that we want pass through the coating , n is the refraction index