Schlick's approximation
In 3D computer graphics, Schlick’s approximation, named after Christophe Schlick, is a formula for approximating the contribution of the Fresnel factor in the specular reflection of light from a non-conducting interface (surface) between two media. According to Schlick’s model, the specular reflection coefficient R can be approximated by: R ( θ ) = R 0 + ( 1 − R 0 ) ( 1 − cos θ ) 5 {\displaystyle R(\theta )=R_{0}+(1-R_{0})(1-\cos \theta )^{5}} where R 0 = ( n 1 − n 2 n 1 + n 2 ) 2 {\displaystyle R_{0}=\left({\frac {n_{1}-n_{2}}{n_{1}+n_{2}}}\right)^{2}} where θ {\displaystyle \theta } is half the angle between the incoming and outgoing light directions.