How Do You Calculate Reflectance?

How Do You Calculate Reflectance? Reflectivity can be calculated as p(y) = Gr(y)/Gi(y) where p is the reflectivity, y is the wavelength of the light, Gr is the reflected radiation and Gi is the incident radiation. Calculate reflectance from the reflectivity. Reflectance is the square of the reflectivity so q(y) = (Gr(y)/Gi(y))^2. How do you