<Dd> n 1 = n 0 n S (\ displaystyle n_ (1) = (\ sqrt (n_ (0) n_ (S)))), </Dd> <P> where n 1 (\ displaystyle n_ (1)) is the index of the thin layer, and n 0 (\ displaystyle n_ (0)) and n S (\ displaystyle n_ (S)) are the indices of the two media . The optimum refractive indices for multiple coating layers at angles of incidence other than 0 ° is given by Moreno et al. (2005). </P> <P> Such coatings can reduce the reflection for ordinary glass from about 4% per surface to around 2% . These were the first type of antireflection coating known, having been discovered by Lord Rayleigh in 1886 . He found that old, slightly tarnished pieces of glass transmitted more light than new, clean pieces due to this effect . </P> <P> Practical antireflection coatings rely on an intermediate layer not only for its direct reduction of reflection coefficient, but also use the interference effect of a thin layer . If the layer's thickness is controlled precisely such that it is exactly one - quarter of the wavelength of the light (a quarter - wave coating), the reflections from the front and back sides of the thin layer will destructively interfere and cancel each other . </P>

The amount of light reflected from the front surface of common window glass is about