Anti-reflection of sunglasses

A common problem with sunglasses is rear glare, which is caused when light hits the back of the lens and then reflects back into your eyes. The role of the anti-reflective protective coating is to reduce this reflection of light from the lens. Like the scratch protection, the anti-reflective coating is a strong, thin film on the lens. The refractive index of the antireflective coating substance is between that of air and glass. This makes the intensity of light reflected by the inner and outer surfaces of the film almost equal. When the thickness of the film is about a quarter of the wavelength of the light wave, the light reflected from the outer and inner surfaces of the film cancels each other out through cancelling interference, thus minimizing the glare you see. Anti-reflective coatings are also applied to the front surface of refractive contact lenses and some sunglasses to eliminate "hot spots" caused by the lens reflecting bright light.