In 1955, Ron Giovanelli published explicit expressions for several cases of interest which are touted as exact solutions to the radiative transfer equation for a semi-infinite ideal diffuser.  His solutions have become the standard against which results from approximate theoretical treatments are measured.  Many of the solutions appear deceptively simple due to the work of Subrahmanyan (Chandra) Chandrasekhar. For example, the total reflectance for light incident in the direction μ is 
Here  is known as the albedo of single scatter , representing the fraction of the radiation lost by scattering in a medium where both absorption () and scattering () take place. The function  is called the H-integral, the values of which were tabulated by Chandrasekhar.